R. Saathof
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1
The use of lasers for satellite communication has recently become a growing field. However, a major challenge in their use is the distortion caused by the atmosphere. The distortion that this study focuses on is optical turbulence. The strength of optical turbulence is related to fluctuations in the refractive index of air and is generally described by Cn². There is a growing body of literature that aims to measure this Cn². One of the methods uses radar, and works by receiving backscattered echoes from turbulent eddies under clear-sky conditions, also known as Bragg scattering. This thesis investigates whether this method, that has so far only been applied to pulsed Doppler weather radars, can also be used with an S-band Frequency-Modulated Continuous-Wave (FMCW) radar.
In this work numerical radar data were used to filter out noise and isolate Bragg scattering. When only clear-sky days in June were included, the results from the 12 selected days showed an average correlation of 0.48 when compared with scintillometer validation data. This is higher than the correlation coefficient of 0.34 found using the pulse-Doppler radar method. However the results also showed a large systematic error, which was found to be related to calibration issues of the used radar. Because this error remained relatively stable over time, a correction factor could potentially be applied to compensate for it. Overall, the results indicate that it is possible to measure optical turbulence using vertical reflectivity measurements from a FMCW radar, although further research and improvements are needed before the method can be used operationally. ...
In this work numerical radar data were used to filter out noise and isolate Bragg scattering. When only clear-sky days in June were included, the results from the 12 selected days showed an average correlation of 0.48 when compared with scintillometer validation data. This is higher than the correlation coefficient of 0.34 found using the pulse-Doppler radar method. However the results also showed a large systematic error, which was found to be related to calibration issues of the used radar. Because this error remained relatively stable over time, a correction factor could potentially be applied to compensate for it. Overall, the results indicate that it is possible to measure optical turbulence using vertical reflectivity measurements from a FMCW radar, although further research and improvements are needed before the method can be used operationally. ...
The use of lasers for satellite communication has recently become a growing field. However, a major challenge in their use is the distortion caused by the atmosphere. The distortion that this study focuses on is optical turbulence. The strength of optical turbulence is related to fluctuations in the refractive index of air and is generally described by Cn². There is a growing body of literature that aims to measure this Cn². One of the methods uses radar, and works by receiving backscattered echoes from turbulent eddies under clear-sky conditions, also known as Bragg scattering. This thesis investigates whether this method, that has so far only been applied to pulsed Doppler weather radars, can also be used with an S-band Frequency-Modulated Continuous-Wave (FMCW) radar.
In this work numerical radar data were used to filter out noise and isolate Bragg scattering. When only clear-sky days in June were included, the results from the 12 selected days showed an average correlation of 0.48 when compared with scintillometer validation data. This is higher than the correlation coefficient of 0.34 found using the pulse-Doppler radar method. However the results also showed a large systematic error, which was found to be related to calibration issues of the used radar. Because this error remained relatively stable over time, a correction factor could potentially be applied to compensate for it. Overall, the results indicate that it is possible to measure optical turbulence using vertical reflectivity measurements from a FMCW radar, although further research and improvements are needed before the method can be used operationally.
In this work numerical radar data were used to filter out noise and isolate Bragg scattering. When only clear-sky days in June were included, the results from the 12 selected days showed an average correlation of 0.48 when compared with scintillometer validation data. This is higher than the correlation coefficient of 0.34 found using the pulse-Doppler radar method. However the results also showed a large systematic error, which was found to be related to calibration issues of the used radar. Because this error remained relatively stable over time, a correction factor could potentially be applied to compensate for it. Overall, the results indicate that it is possible to measure optical turbulence using vertical reflectivity measurements from a FMCW radar, although further research and improvements are needed before the method can be used operationally.
A portable, camera-based fiducial positioning approach intended for general contact NDT is presented and experimentally assessed, with phasedarray ultrasonic testing (PAUT) used as the demonstrator application. The positioning method employs inside-out tracking, with a camera rigidly mounted to the probe and a 3D fiducial reference object fixed in the inspection environment. The probe 6-DoF pose is obtained by estimating the camera pose and applying a pivot-based co-calibration to express the phased-array measurement in the fiducial frame. A holistic assessment is performed by (i) quantifying in-plane and out-of-plane translation repeatability and rotational repeatability over relevant working distances and viewing angles, (ii) characterising the camera-to-probe co-calibration accuracy, and (iii) propagating these contributions to an end-toend defect localisation error. Experiments show submillimeter translation repeatability within a practical operating range of 1.5–2.0 m, degrading to a few millimeters at∼3 m and for larger off-axis viewing angles. The pivot co-calibration achieves an RMS error of approximately 1.5 mm relative to a calibration jig. End-to-end validation on a GFRP plate demonstrates millimeter-scale defect localisation and sizing, with sub-millimetre in-plane shift relative to a reference C-scan. These results indicate that fiducial-based positioning provides accuracy sufficient for contact PAUT and constitutes a viable alternative to encoder-based tracking for portable NDT.
...
A portable, camera-based fiducial positioning approach intended for general contact NDT is presented and experimentally assessed, with phasedarray ultrasonic testing (PAUT) used as the demonstrator application. The positioning method employs inside-out tracking, with a camera rigidly mounted to the probe and a 3D fiducial reference object fixed in the inspection environment. The probe 6-DoF pose is obtained by estimating the camera pose and applying a pivot-based co-calibration to express the phased-array measurement in the fiducial frame. A holistic assessment is performed by (i) quantifying in-plane and out-of-plane translation repeatability and rotational repeatability over relevant working distances and viewing angles, (ii) characterising the camera-to-probe co-calibration accuracy, and (iii) propagating these contributions to an end-toend defect localisation error. Experiments show submillimeter translation repeatability within a practical operating range of 1.5–2.0 m, degrading to a few millimeters at∼3 m and for larger off-axis viewing angles. The pivot co-calibration achieves an RMS error of approximately 1.5 mm relative to a calibration jig. End-to-end validation on a GFRP plate demonstrates millimeter-scale defect localisation and sizing, with sub-millimetre in-plane shift relative to a reference C-scan. These results indicate that fiducial-based positioning provides accuracy sufficient for contact PAUT and constitutes a viable alternative to encoder-based tracking for portable NDT.
Pointing calibration for laser satellite communications
An in-orbit pointing error prediction strategy to increase acquisition performance of Optical Communications Terminals
Master thesis
(2026)
-
O.P. Heukelom, R. Saathof, I.F. Walford, R.N. Buitenhuis, A. Cervone, D. Dirkx
Laser satellite communications are increasingly being adopted throughout the space sector, with large-scale constellations relying on optical links to provide high-data-rate and secure communications. A key challenge in optical communications is the acquisition phase, during which two optical communication terminals (OCTs) must establish a bidirectional link despite the presence of pointing uncertainties. Reducing these uncertainties can significantly improve acquisition performance and reduce the associated search burden.
This thesis investigates an in-orbit calibration strategy for predicting OCT pointing errors using sensors and telemetry already available within the terminal. A review of existing calibration approaches identified a research gap in the use of OCT-internal measurements for the continuous estimation and prediction of pointing errors throughout the mission lifetime. To address this gap, a mission-lifetime calibration strategy was developed and evaluated using a dedicated simulation and development framework.
The dominant pointing-error contributors considered in this work are mechanical alignment errors, thermal distortions, satellite attitude determination and control system (ADCS) errors, and counter-satellite propagation errors. It is shown that a significant portion of the resulting pointing error can be predicted using operational parameters such as time, temperature, and gimbal orientation. An ordinary least squares regression framework was developed using time, temperature, azimuth, and elevation as inputs, and pointing errors in the terminal frame as outputs. The calibration model is continually updated using data collected during operational tracking phases, enabling the prediction of pointing errors under a wide range of mission conditions.
Simulation results demonstrate that the proposed approach can substantially reduce residual pointing errors and generalise across multiple mission scenarios and link geometries. Furthermore, calibration performance improves as calibration data are accumulated throughout the mission lifetime. The results also show that acquisition performance can be enhanced through informed acquisition scheduling, whereby links are established during periods of favourable operating conditions and reduced predicted pointing errors.
Overall, this work demonstrates that mission-lifetime in-orbit calibration can reduce pointing uncertainty, improve acquisition performance, and increase the operational robustness of optical communication terminals without requiring additional dedicated calibration hardware. ...
This thesis investigates an in-orbit calibration strategy for predicting OCT pointing errors using sensors and telemetry already available within the terminal. A review of existing calibration approaches identified a research gap in the use of OCT-internal measurements for the continuous estimation and prediction of pointing errors throughout the mission lifetime. To address this gap, a mission-lifetime calibration strategy was developed and evaluated using a dedicated simulation and development framework.
The dominant pointing-error contributors considered in this work are mechanical alignment errors, thermal distortions, satellite attitude determination and control system (ADCS) errors, and counter-satellite propagation errors. It is shown that a significant portion of the resulting pointing error can be predicted using operational parameters such as time, temperature, and gimbal orientation. An ordinary least squares regression framework was developed using time, temperature, azimuth, and elevation as inputs, and pointing errors in the terminal frame as outputs. The calibration model is continually updated using data collected during operational tracking phases, enabling the prediction of pointing errors under a wide range of mission conditions.
Simulation results demonstrate that the proposed approach can substantially reduce residual pointing errors and generalise across multiple mission scenarios and link geometries. Furthermore, calibration performance improves as calibration data are accumulated throughout the mission lifetime. The results also show that acquisition performance can be enhanced through informed acquisition scheduling, whereby links are established during periods of favourable operating conditions and reduced predicted pointing errors.
Overall, this work demonstrates that mission-lifetime in-orbit calibration can reduce pointing uncertainty, improve acquisition performance, and increase the operational robustness of optical communication terminals without requiring additional dedicated calibration hardware. ...
Laser satellite communications are increasingly being adopted throughout the space sector, with large-scale constellations relying on optical links to provide high-data-rate and secure communications. A key challenge in optical communications is the acquisition phase, during which two optical communication terminals (OCTs) must establish a bidirectional link despite the presence of pointing uncertainties. Reducing these uncertainties can significantly improve acquisition performance and reduce the associated search burden.
This thesis investigates an in-orbit calibration strategy for predicting OCT pointing errors using sensors and telemetry already available within the terminal. A review of existing calibration approaches identified a research gap in the use of OCT-internal measurements for the continuous estimation and prediction of pointing errors throughout the mission lifetime. To address this gap, a mission-lifetime calibration strategy was developed and evaluated using a dedicated simulation and development framework.
The dominant pointing-error contributors considered in this work are mechanical alignment errors, thermal distortions, satellite attitude determination and control system (ADCS) errors, and counter-satellite propagation errors. It is shown that a significant portion of the resulting pointing error can be predicted using operational parameters such as time, temperature, and gimbal orientation. An ordinary least squares regression framework was developed using time, temperature, azimuth, and elevation as inputs, and pointing errors in the terminal frame as outputs. The calibration model is continually updated using data collected during operational tracking phases, enabling the prediction of pointing errors under a wide range of mission conditions.
Simulation results demonstrate that the proposed approach can substantially reduce residual pointing errors and generalise across multiple mission scenarios and link geometries. Furthermore, calibration performance improves as calibration data are accumulated throughout the mission lifetime. The results also show that acquisition performance can be enhanced through informed acquisition scheduling, whereby links are established during periods of favourable operating conditions and reduced predicted pointing errors.
Overall, this work demonstrates that mission-lifetime in-orbit calibration can reduce pointing uncertainty, improve acquisition performance, and increase the operational robustness of optical communication terminals without requiring additional dedicated calibration hardware.
This thesis investigates an in-orbit calibration strategy for predicting OCT pointing errors using sensors and telemetry already available within the terminal. A review of existing calibration approaches identified a research gap in the use of OCT-internal measurements for the continuous estimation and prediction of pointing errors throughout the mission lifetime. To address this gap, a mission-lifetime calibration strategy was developed and evaluated using a dedicated simulation and development framework.
The dominant pointing-error contributors considered in this work are mechanical alignment errors, thermal distortions, satellite attitude determination and control system (ADCS) errors, and counter-satellite propagation errors. It is shown that a significant portion of the resulting pointing error can be predicted using operational parameters such as time, temperature, and gimbal orientation. An ordinary least squares regression framework was developed using time, temperature, azimuth, and elevation as inputs, and pointing errors in the terminal frame as outputs. The calibration model is continually updated using data collected during operational tracking phases, enabling the prediction of pointing errors under a wide range of mission conditions.
Simulation results demonstrate that the proposed approach can substantially reduce residual pointing errors and generalise across multiple mission scenarios and link geometries. Furthermore, calibration performance improves as calibration data are accumulated throughout the mission lifetime. The results also show that acquisition performance can be enhanced through informed acquisition scheduling, whereby links are established during periods of favourable operating conditions and reduced predicted pointing errors.
Overall, this work demonstrates that mission-lifetime in-orbit calibration can reduce pointing uncertainty, improve acquisition performance, and increase the operational robustness of optical communication terminals without requiring additional dedicated calibration hardware.
Laser communication is seen as the future of high-speed communication in space and a potential key technology for the future. This is due to low beam divergence, around three orders of magnitude less than that of for similarly sized microwave based radio frequency systems. This allows higher signal-to-noise ratios due to increased signal power transferred. Additionally, the reduced beam divergence implies no overlap with other optical links, eliminating cross interference. As a result, laser communication can leverage larger bandwidths. Nevertheless, low beam divergence has also meant that laser communication until now has been point-to-point, limiting scalability and reducing reliability. Multi-beam laser communication terminals (MBTs) offer point-to-multipoint laser communication, implying a scalable solution to bringing this technology into globally available networks....
...
Laser communication is seen as the future of high-speed communication in space and a potential key technology for the future. This is due to low beam divergence, around three orders of magnitude less than that of for similarly sized microwave based radio frequency systems. This allows higher signal-to-noise ratios due to increased signal power transferred. Additionally, the reduced beam divergence implies no overlap with other optical links, eliminating cross interference. As a result, laser communication can leverage larger bandwidths. Nevertheless, low beam divergence has also meant that laser communication until now has been point-to-point, limiting scalability and reducing reliability. Multi-beam laser communication terminals (MBTs) offer point-to-multipoint laser communication, implying a scalable solution to bringing this technology into globally available networks....
Free-space optical communication (FSOC) is a key technology to meet the growing demand for high-bandwidth, secure, and energy-efficient data links.
However, the atmospheric channel introduces a major challenge: optical turbulence (OT). Turbulent fluctuations of the refractive index, driven by wind shear and buoyancy in the atmosphere, distort the propagating optical beam, degrading communication performance. This dissertation investigates the modelling of optical turbulence, quantified through the refractive index structure parameter Cn2, along two complementary avenues: traditional numerical weather prediction (NWP) using mesoscale models and machine learning (ML) techniques.
The first part establishes the state of the art in mesoscale Cn2 modelling for FSOC. Chapter 2 presents a systematic intercomparison of the three main classes of Cn2 parameterizations -- flux-based, gradient-based, and variance-based -- applied to both observed data and output from a numerical mesoscale model.
Evaluated against scintillometer observations, the variance-based parameterization yields the best overall performance and, unlike the other two, is not restricted to the atmospheric surface layer. Building on this foundation, chapter 3 proposes an end-to-end framework that translates Cn2 estimates into FSOC link performance metrics, specifically turbulence-induced losses and a theoretically achievable information rate (generalized mutual information, GMI).
Applied to an urban example link, the framework reveals that the sensitivity of the estimated FSOC performance to Cn2 errors strongly depends on the specific link. Reporting Cn2 model errors alone is therefore considered insufficient for FSOC, and end-to-end assessments of link performance are needed.
Running mesoscale models is computationally expensive, and the traditional parameterizations used to obtain Cn2 -- while physically motivated -- are often limited in their applicability or accuracy. Machine learning offers a promising alternative by learning complex relationships directly from data, as explored in the second part of this dissertation. Chapter 4 introduces OTCliM, a gradient boosting-based methodology that relates globally available ERA5 reanalysis data to observed near-surface Cn2. Across 17 diverse stations in New York State, OTCliM trained on just one year of observations accurately extrapolates Cn2 over four held-out years. However, the resulting models are limited to near-surface Cn2, which is sufficient for terrestrial links but not for satellite-to-ground applications that require vertical profiles. To extend modelling into the vertical, chapter 5 introduces Π-ML, a physics-inspired ML framework that combines automated dimensional analysis with gradient boosting. By expressing inputs and outputs as non-dimensional groups grounded in physical principles, Π-ML derives an interpretable, data-driven similarity theory for Cn2 in the atmospheric surface layer. The framework achieves high accuracy under both stable and unstable atmospheric conditions and identifies scalings that are physically consistent with established theories. Finally, chapter 6 addresses the full atmospheric column by developing OTProf. This deep-learning-based model estimates Cn2 profiles of high vertical resolution from low-resolution ERA5 pressure-level inputs. Trained on one year of mesoscale simulations, the model substantially outperforms the commonly used Hufnagel-Valley analytical model.
The estimated profiles exhibit a physically realistic vertical structure, although ML-typical smoothing leads to some underestimation of integrated turbulence parameters, such as the Fried parameter and the scintillation index.
Nevertheless, OTProf is regarded as a computationally efficient and considerably more accurate approach compared to traditional analytical models.
Taken together, this dissertation demonstrates that both numerical mesoscale modelling and machine learning deliver practical advances for optical turbulence estimation and FSOC applications. The overarching conclusion, however, is that the greatest potential lies in combining the two paradigms, which is viewed as a promising direction for future research. ...
However, the atmospheric channel introduces a major challenge: optical turbulence (OT). Turbulent fluctuations of the refractive index, driven by wind shear and buoyancy in the atmosphere, distort the propagating optical beam, degrading communication performance. This dissertation investigates the modelling of optical turbulence, quantified through the refractive index structure parameter Cn2, along two complementary avenues: traditional numerical weather prediction (NWP) using mesoscale models and machine learning (ML) techniques.
The first part establishes the state of the art in mesoscale Cn2 modelling for FSOC. Chapter 2 presents a systematic intercomparison of the three main classes of Cn2 parameterizations -- flux-based, gradient-based, and variance-based -- applied to both observed data and output from a numerical mesoscale model.
Evaluated against scintillometer observations, the variance-based parameterization yields the best overall performance and, unlike the other two, is not restricted to the atmospheric surface layer. Building on this foundation, chapter 3 proposes an end-to-end framework that translates Cn2 estimates into FSOC link performance metrics, specifically turbulence-induced losses and a theoretically achievable information rate (generalized mutual information, GMI).
Applied to an urban example link, the framework reveals that the sensitivity of the estimated FSOC performance to Cn2 errors strongly depends on the specific link. Reporting Cn2 model errors alone is therefore considered insufficient for FSOC, and end-to-end assessments of link performance are needed.
Running mesoscale models is computationally expensive, and the traditional parameterizations used to obtain Cn2 -- while physically motivated -- are often limited in their applicability or accuracy. Machine learning offers a promising alternative by learning complex relationships directly from data, as explored in the second part of this dissertation. Chapter 4 introduces OTCliM, a gradient boosting-based methodology that relates globally available ERA5 reanalysis data to observed near-surface Cn2. Across 17 diverse stations in New York State, OTCliM trained on just one year of observations accurately extrapolates Cn2 over four held-out years. However, the resulting models are limited to near-surface Cn2, which is sufficient for terrestrial links but not for satellite-to-ground applications that require vertical profiles. To extend modelling into the vertical, chapter 5 introduces Π-ML, a physics-inspired ML framework that combines automated dimensional analysis with gradient boosting. By expressing inputs and outputs as non-dimensional groups grounded in physical principles, Π-ML derives an interpretable, data-driven similarity theory for Cn2 in the atmospheric surface layer. The framework achieves high accuracy under both stable and unstable atmospheric conditions and identifies scalings that are physically consistent with established theories. Finally, chapter 6 addresses the full atmospheric column by developing OTProf. This deep-learning-based model estimates Cn2 profiles of high vertical resolution from low-resolution ERA5 pressure-level inputs. Trained on one year of mesoscale simulations, the model substantially outperforms the commonly used Hufnagel-Valley analytical model.
The estimated profiles exhibit a physically realistic vertical structure, although ML-typical smoothing leads to some underestimation of integrated turbulence parameters, such as the Fried parameter and the scintillation index.
Nevertheless, OTProf is regarded as a computationally efficient and considerably more accurate approach compared to traditional analytical models.
Taken together, this dissertation demonstrates that both numerical mesoscale modelling and machine learning deliver practical advances for optical turbulence estimation and FSOC applications. The overarching conclusion, however, is that the greatest potential lies in combining the two paradigms, which is viewed as a promising direction for future research. ...
Free-space optical communication (FSOC) is a key technology to meet the growing demand for high-bandwidth, secure, and energy-efficient data links.
However, the atmospheric channel introduces a major challenge: optical turbulence (OT). Turbulent fluctuations of the refractive index, driven by wind shear and buoyancy in the atmosphere, distort the propagating optical beam, degrading communication performance. This dissertation investigates the modelling of optical turbulence, quantified through the refractive index structure parameter Cn2, along two complementary avenues: traditional numerical weather prediction (NWP) using mesoscale models and machine learning (ML) techniques.
The first part establishes the state of the art in mesoscale Cn2 modelling for FSOC. Chapter 2 presents a systematic intercomparison of the three main classes of Cn2 parameterizations -- flux-based, gradient-based, and variance-based -- applied to both observed data and output from a numerical mesoscale model.
Evaluated against scintillometer observations, the variance-based parameterization yields the best overall performance and, unlike the other two, is not restricted to the atmospheric surface layer. Building on this foundation, chapter 3 proposes an end-to-end framework that translates Cn2 estimates into FSOC link performance metrics, specifically turbulence-induced losses and a theoretically achievable information rate (generalized mutual information, GMI).
Applied to an urban example link, the framework reveals that the sensitivity of the estimated FSOC performance to Cn2 errors strongly depends on the specific link. Reporting Cn2 model errors alone is therefore considered insufficient for FSOC, and end-to-end assessments of link performance are needed.
Running mesoscale models is computationally expensive, and the traditional parameterizations used to obtain Cn2 -- while physically motivated -- are often limited in their applicability or accuracy. Machine learning offers a promising alternative by learning complex relationships directly from data, as explored in the second part of this dissertation. Chapter 4 introduces OTCliM, a gradient boosting-based methodology that relates globally available ERA5 reanalysis data to observed near-surface Cn2. Across 17 diverse stations in New York State, OTCliM trained on just one year of observations accurately extrapolates Cn2 over four held-out years. However, the resulting models are limited to near-surface Cn2, which is sufficient for terrestrial links but not for satellite-to-ground applications that require vertical profiles. To extend modelling into the vertical, chapter 5 introduces Π-ML, a physics-inspired ML framework that combines automated dimensional analysis with gradient boosting. By expressing inputs and outputs as non-dimensional groups grounded in physical principles, Π-ML derives an interpretable, data-driven similarity theory for Cn2 in the atmospheric surface layer. The framework achieves high accuracy under both stable and unstable atmospheric conditions and identifies scalings that are physically consistent with established theories. Finally, chapter 6 addresses the full atmospheric column by developing OTProf. This deep-learning-based model estimates Cn2 profiles of high vertical resolution from low-resolution ERA5 pressure-level inputs. Trained on one year of mesoscale simulations, the model substantially outperforms the commonly used Hufnagel-Valley analytical model.
The estimated profiles exhibit a physically realistic vertical structure, although ML-typical smoothing leads to some underestimation of integrated turbulence parameters, such as the Fried parameter and the scintillation index.
Nevertheless, OTProf is regarded as a computationally efficient and considerably more accurate approach compared to traditional analytical models.
Taken together, this dissertation demonstrates that both numerical mesoscale modelling and machine learning deliver practical advances for optical turbulence estimation and FSOC applications. The overarching conclusion, however, is that the greatest potential lies in combining the two paradigms, which is viewed as a promising direction for future research.
However, the atmospheric channel introduces a major challenge: optical turbulence (OT). Turbulent fluctuations of the refractive index, driven by wind shear and buoyancy in the atmosphere, distort the propagating optical beam, degrading communication performance. This dissertation investigates the modelling of optical turbulence, quantified through the refractive index structure parameter Cn2, along two complementary avenues: traditional numerical weather prediction (NWP) using mesoscale models and machine learning (ML) techniques.
The first part establishes the state of the art in mesoscale Cn2 modelling for FSOC. Chapter 2 presents a systematic intercomparison of the three main classes of Cn2 parameterizations -- flux-based, gradient-based, and variance-based -- applied to both observed data and output from a numerical mesoscale model.
Evaluated against scintillometer observations, the variance-based parameterization yields the best overall performance and, unlike the other two, is not restricted to the atmospheric surface layer. Building on this foundation, chapter 3 proposes an end-to-end framework that translates Cn2 estimates into FSOC link performance metrics, specifically turbulence-induced losses and a theoretically achievable information rate (generalized mutual information, GMI).
Applied to an urban example link, the framework reveals that the sensitivity of the estimated FSOC performance to Cn2 errors strongly depends on the specific link. Reporting Cn2 model errors alone is therefore considered insufficient for FSOC, and end-to-end assessments of link performance are needed.
Running mesoscale models is computationally expensive, and the traditional parameterizations used to obtain Cn2 -- while physically motivated -- are often limited in their applicability or accuracy. Machine learning offers a promising alternative by learning complex relationships directly from data, as explored in the second part of this dissertation. Chapter 4 introduces OTCliM, a gradient boosting-based methodology that relates globally available ERA5 reanalysis data to observed near-surface Cn2. Across 17 diverse stations in New York State, OTCliM trained on just one year of observations accurately extrapolates Cn2 over four held-out years. However, the resulting models are limited to near-surface Cn2, which is sufficient for terrestrial links but not for satellite-to-ground applications that require vertical profiles. To extend modelling into the vertical, chapter 5 introduces Π-ML, a physics-inspired ML framework that combines automated dimensional analysis with gradient boosting. By expressing inputs and outputs as non-dimensional groups grounded in physical principles, Π-ML derives an interpretable, data-driven similarity theory for Cn2 in the atmospheric surface layer. The framework achieves high accuracy under both stable and unstable atmospheric conditions and identifies scalings that are physically consistent with established theories. Finally, chapter 6 addresses the full atmospheric column by developing OTProf. This deep-learning-based model estimates Cn2 profiles of high vertical resolution from low-resolution ERA5 pressure-level inputs. Trained on one year of mesoscale simulations, the model substantially outperforms the commonly used Hufnagel-Valley analytical model.
The estimated profiles exhibit a physically realistic vertical structure, although ML-typical smoothing leads to some underestimation of integrated turbulence parameters, such as the Fried parameter and the scintillation index.
Nevertheless, OTProf is regarded as a computationally efficient and considerably more accurate approach compared to traditional analytical models.
Taken together, this dissertation demonstrates that both numerical mesoscale modelling and machine learning deliver practical advances for optical turbulence estimation and FSOC applications. The overarching conclusion, however, is that the greatest potential lies in combining the two paradigms, which is viewed as a promising direction for future research.
Master thesis
(2025)
-
T.S. Spee, A. Menicucci, Javier Alonso-Mora, David Rijlaarsdam, C.J.M. Verhoeven, R. Saathof
Autonomous planetary rovers require obstacle detection capabilities to navigate hazardous terrain without Earth-based intervention, yet currently deployed methods are limited. This research develops and validates a complete deep learning system for autonomous rock detection on a resource-constrained planetary rover.
We present a lightweight MobileNetV2-based U-Net architecture with dual attention mechanisms, optimized for edge deployment with only 0.31 million parameters. A new dataset MarsTanYard was created via a semi-automated dataset creation pipeline, enabling efficient annotation of Mars-analogue terrain imagery. Our deep learning network was trained on this dataset and integrated with a ROS2 navigation stack through a modular architecture that transforms segmentation masks into 2D occupancy grids that can be used for rover path planning. Our network achieves a 77% intersection-over-union accuracy for rock segmentation, and physical validation on a testing rover in a Mars analogue environment demonstrates a 94% detection rate for large rocks at close-range. An inference time of 4.49ms was achieved on the target rover hardware using model optimization techniques. The system maintains reliable operation across varying lighting conditions with less than 15% performance degradation.
Results show theoretical collision probability of 7.8 × 10^-7 per rock encounter, enabling months of autonomous operation for typical planetary missions. This work provides an end-to-end validation of the deep learning obstacle detection system, establishing a foundation for enhanced rover autonomy in future Mars exploration missions. ...
We present a lightweight MobileNetV2-based U-Net architecture with dual attention mechanisms, optimized for edge deployment with only 0.31 million parameters. A new dataset MarsTanYard was created via a semi-automated dataset creation pipeline, enabling efficient annotation of Mars-analogue terrain imagery. Our deep learning network was trained on this dataset and integrated with a ROS2 navigation stack through a modular architecture that transforms segmentation masks into 2D occupancy grids that can be used for rover path planning. Our network achieves a 77% intersection-over-union accuracy for rock segmentation, and physical validation on a testing rover in a Mars analogue environment demonstrates a 94% detection rate for large rocks at close-range. An inference time of 4.49ms was achieved on the target rover hardware using model optimization techniques. The system maintains reliable operation across varying lighting conditions with less than 15% performance degradation.
Results show theoretical collision probability of 7.8 × 10^-7 per rock encounter, enabling months of autonomous operation for typical planetary missions. This work provides an end-to-end validation of the deep learning obstacle detection system, establishing a foundation for enhanced rover autonomy in future Mars exploration missions. ...
Autonomous planetary rovers require obstacle detection capabilities to navigate hazardous terrain without Earth-based intervention, yet currently deployed methods are limited. This research develops and validates a complete deep learning system for autonomous rock detection on a resource-constrained planetary rover.
We present a lightweight MobileNetV2-based U-Net architecture with dual attention mechanisms, optimized for edge deployment with only 0.31 million parameters. A new dataset MarsTanYard was created via a semi-automated dataset creation pipeline, enabling efficient annotation of Mars-analogue terrain imagery. Our deep learning network was trained on this dataset and integrated with a ROS2 navigation stack through a modular architecture that transforms segmentation masks into 2D occupancy grids that can be used for rover path planning. Our network achieves a 77% intersection-over-union accuracy for rock segmentation, and physical validation on a testing rover in a Mars analogue environment demonstrates a 94% detection rate for large rocks at close-range. An inference time of 4.49ms was achieved on the target rover hardware using model optimization techniques. The system maintains reliable operation across varying lighting conditions with less than 15% performance degradation.
Results show theoretical collision probability of 7.8 × 10^-7 per rock encounter, enabling months of autonomous operation for typical planetary missions. This work provides an end-to-end validation of the deep learning obstacle detection system, establishing a foundation for enhanced rover autonomy in future Mars exploration missions.
We present a lightweight MobileNetV2-based U-Net architecture with dual attention mechanisms, optimized for edge deployment with only 0.31 million parameters. A new dataset MarsTanYard was created via a semi-automated dataset creation pipeline, enabling efficient annotation of Mars-analogue terrain imagery. Our deep learning network was trained on this dataset and integrated with a ROS2 navigation stack through a modular architecture that transforms segmentation masks into 2D occupancy grids that can be used for rover path planning. Our network achieves a 77% intersection-over-union accuracy for rock segmentation, and physical validation on a testing rover in a Mars analogue environment demonstrates a 94% detection rate for large rocks at close-range. An inference time of 4.49ms was achieved on the target rover hardware using model optimization techniques. The system maintains reliable operation across varying lighting conditions with less than 15% performance degradation.
Results show theoretical collision probability of 7.8 × 10^-7 per rock encounter, enabling months of autonomous operation for typical planetary missions. This work provides an end-to-end validation of the deep learning obstacle detection system, establishing a foundation for enhanced rover autonomy in future Mars exploration missions.
Master thesis
(2025)
-
A. Bradosche Pallarés, Rudolf Saathof, Sven Van Binsbergen, Rene van Paassen, Bert Vermeersen
Target-in-the-loop (TIL) systems are key to engaging aerial threats and enabling laser processing. This work simulates a TIL system and evaluates its performance under varying atmospheric turbulence and target distances. The goal is to assess how these factors affect energy delivery and real-world viability. A computational model was developed using standard wavefront propagation to account for turbulence and target surface roughness. The simulation allows controlled changes in turbulence strength and range. An experimental setup was also created to validate the results. Findings show that compensating for surface roughness is crucial, and system performance improves significantly with a controller—boosting peak intensity by up to 60% and power in the bucket by 10%. A tradeoff exists between distance and turbulence strength, but adaptive optics can help extend operational range.
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Target-in-the-loop (TIL) systems are key to engaging aerial threats and enabling laser processing. This work simulates a TIL system and evaluates its performance under varying atmospheric turbulence and target distances. The goal is to assess how these factors affect energy delivery and real-world viability. A computational model was developed using standard wavefront propagation to account for turbulence and target surface roughness. The simulation allows controlled changes in turbulence strength and range. An experimental setup was also created to validate the results. Findings show that compensating for surface roughness is crucial, and system performance improves significantly with a controller—boosting peak intensity by up to 60% and power in the bucket by 10%. A tradeoff exists between distance and turbulence strength, but adaptive optics can help extend operational range.
Free-space optical communications on board high-altitude platform stations (HAPS) promises commercial upside for supplying internet connectivity to regions underserved by space constellations. However, platform vibrations and stringent hardware constraints make pointing, acquisition, and tracking (PAT) of optical links difficult to implement. This work investigates the effectiveness of a cascaded control architecture for the combined actuation of a coarse pointing assembly and fine-steering mirror for PAT between HAPS and LEO spacecraft. The laser communications hardware and platform dynamics are simulated in detail, followed by a systematic control design using H∞ optimization. An Extended Kalman Filter combining recorded light measurements from the target and trajectory propagations provide the system with continuous pointing input. Results show that the cascade control architecture can
reject disturbances up to 300Hz in tracking and correct pointing errors up to 40mrad in acquisition. The EKF output accuracy significantly degrades after 15 seconds due to GNSS antenna instability caused by the bending of the HAPS air frame.
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reject disturbances up to 300Hz in tracking and correct pointing errors up to 40mrad in acquisition. The EKF output accuracy significantly degrades after 15 seconds due to GNSS antenna instability caused by the bending of the HAPS air frame.
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Free-space optical communications on board high-altitude platform stations (HAPS) promises commercial upside for supplying internet connectivity to regions underserved by space constellations. However, platform vibrations and stringent hardware constraints make pointing, acquisition, and tracking (PAT) of optical links difficult to implement. This work investigates the effectiveness of a cascaded control architecture for the combined actuation of a coarse pointing assembly and fine-steering mirror for PAT between HAPS and LEO spacecraft. The laser communications hardware and platform dynamics are simulated in detail, followed by a systematic control design using H∞ optimization. An Extended Kalman Filter combining recorded light measurements from the target and trajectory propagations provide the system with continuous pointing input. Results show that the cascade control architecture can
reject disturbances up to 300Hz in tracking and correct pointing errors up to 40mrad in acquisition. The EKF output accuracy significantly degrades after 15 seconds due to GNSS antenna instability caused by the bending of the HAPS air frame.
reject disturbances up to 300Hz in tracking and correct pointing errors up to 40mrad in acquisition. The EKF output accuracy significantly degrades after 15 seconds due to GNSS antenna instability caused by the bending of the HAPS air frame.
Free-space laser communications promise high-data rates for ground-to-space uplinks, but precise beam acquisition remains a critical challenge due to platform attitude errors and atmospheric turbulence. Conventional collimated beacon beams are often constrained by safety regulations, leading to the usage of defocused beams, which also promise efficient acquisition times. This Master thesis conducted at Airbus Netherlands B.V. investigates the near-field turbulence impact of defocused beams on far-field scintillation. The study comprises
theoretical modelling, wavefield propagation simulations, and experimental measurements to examine how varying the transmitter aperture radius affects scintillation relative to collimated beams under different turbulence conditions. The simulations and the theoretical model show that far-field scintillation grows as the beam becomes more defocused with increasing transmitter sizes for different turbulence conditions. Results indicate that while moderate defocusing doesn’t affect propagation performance, excessive defocusing in strong turbulence conditions amplifies irradiance fluctuations, potentially degrading acquisition efficiency from the computed amplitude statistics. Preliminary Experimental breadboard findings confirm the general trend but highlight discrepancies in absolute scintillation values due to laboratory downscaling constraints. ...
theoretical modelling, wavefield propagation simulations, and experimental measurements to examine how varying the transmitter aperture radius affects scintillation relative to collimated beams under different turbulence conditions. The simulations and the theoretical model show that far-field scintillation grows as the beam becomes more defocused with increasing transmitter sizes for different turbulence conditions. Results indicate that while moderate defocusing doesn’t affect propagation performance, excessive defocusing in strong turbulence conditions amplifies irradiance fluctuations, potentially degrading acquisition efficiency from the computed amplitude statistics. Preliminary Experimental breadboard findings confirm the general trend but highlight discrepancies in absolute scintillation values due to laboratory downscaling constraints. ...
Free-space laser communications promise high-data rates for ground-to-space uplinks, but precise beam acquisition remains a critical challenge due to platform attitude errors and atmospheric turbulence. Conventional collimated beacon beams are often constrained by safety regulations, leading to the usage of defocused beams, which also promise efficient acquisition times. This Master thesis conducted at Airbus Netherlands B.V. investigates the near-field turbulence impact of defocused beams on far-field scintillation. The study comprises
theoretical modelling, wavefield propagation simulations, and experimental measurements to examine how varying the transmitter aperture radius affects scintillation relative to collimated beams under different turbulence conditions. The simulations and the theoretical model show that far-field scintillation grows as the beam becomes more defocused with increasing transmitter sizes for different turbulence conditions. Results indicate that while moderate defocusing doesn’t affect propagation performance, excessive defocusing in strong turbulence conditions amplifies irradiance fluctuations, potentially degrading acquisition efficiency from the computed amplitude statistics. Preliminary Experimental breadboard findings confirm the general trend but highlight discrepancies in absolute scintillation values due to laboratory downscaling constraints.
theoretical modelling, wavefield propagation simulations, and experimental measurements to examine how varying the transmitter aperture radius affects scintillation relative to collimated beams under different turbulence conditions. The simulations and the theoretical model show that far-field scintillation grows as the beam becomes more defocused with increasing transmitter sizes for different turbulence conditions. Results indicate that while moderate defocusing doesn’t affect propagation performance, excessive defocusing in strong turbulence conditions amplifies irradiance fluctuations, potentially degrading acquisition efficiency from the computed amplitude statistics. Preliminary Experimental breadboard findings confirm the general trend but highlight discrepancies in absolute scintillation values due to laboratory downscaling constraints.
Free-Space Optical Communication (FSOC) constellations have shown potential to meet future data transport demand by providing high capacity, low latency and secure communication. The relationship between the configuration of the constellation and its service performance is an important factor for FSO hardware development and constellation deployment. However, little research has been dedicated to the configuration-performance relationship and further investigation is warranted. This work therefore investigated the relationship by analysing the service performance of FSOC constellations as a result of input parameters, consisting of Walker parameters, orbital altitude and number of Laser Communication Terminals (LCT) per satellite. To perform the analysis, a numerical FSOC constellation model was built that incorporates physical processes at different time scales stemming from satellite dynamics, platform dynamics and bit processes. Sensitivity analysis shows that performance improves with higher inclination and more orbital planes, yielding gains up to 18.1% and 14.3%, respectively. These improvements result from shorter inter-orbit link distances and greater routing flexibility, which are key characteristics of square mesh topologies. This advantage is confirmed through direct constellation comparisons, where the more naturally square Walker Star configurations (WSC) with polar orbits consistently outperform Walker Delta configurations (WDC) with regularly inclined orbits. The importance of routing flexibility is further highlighted by the superior performance of topologies equipped with 4 LCTs per satellite as opposed to 3, with performance gains up to 19.0%.
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Free-Space Optical Communication (FSOC) constellations have shown potential to meet future data transport demand by providing high capacity, low latency and secure communication. The relationship between the configuration of the constellation and its service performance is an important factor for FSO hardware development and constellation deployment. However, little research has been dedicated to the configuration-performance relationship and further investigation is warranted. This work therefore investigated the relationship by analysing the service performance of FSOC constellations as a result of input parameters, consisting of Walker parameters, orbital altitude and number of Laser Communication Terminals (LCT) per satellite. To perform the analysis, a numerical FSOC constellation model was built that incorporates physical processes at different time scales stemming from satellite dynamics, platform dynamics and bit processes. Sensitivity analysis shows that performance improves with higher inclination and more orbital planes, yielding gains up to 18.1% and 14.3%, respectively. These improvements result from shorter inter-orbit link distances and greater routing flexibility, which are key characteristics of square mesh topologies. This advantage is confirmed through direct constellation comparisons, where the more naturally square Walker Star configurations (WSC) with polar orbits consistently outperform Walker Delta configurations (WDC) with regularly inclined orbits. The importance of routing flexibility is further highlighted by the superior performance of topologies equipped with 4 LCTs per satellite as opposed to 3, with performance gains up to 19.0%.
Coherent Free Space Detection for Differential Phase Shift Keying
A Hardware-Based Approach to Optical Communication
As demand for high-bandwidth data transmission continues to increase, future satellite constellations can leverage the benefits of free space optical communication, which provides significant advantages compared to traditional radio frequency systems. Despite the development of satellite laser communication terminals (LCTs) in recent years, one major challenge remains; coupling the incoming signal into an optical fiber. In addition, most terminals use intensity modulation to encode data, which is limited in its ability to reach high data rates. So-called coherent modulation schemes offer superior performance but are not widely implemented in satellite LCT’s yet. A system that avoids fiber coupling while using coherent modulation could simplify designs, reduce complexity, and improve performance. This thesis presents the design, implementation, and evaluation of such a coherent free space optical detection system. Differential Phase Shift Keying (DPSK) was chosen as the modulation scheme due to its balance of power efficiency and implementation simplicity, delivering performance comparable to other coherent schemes with a less complex receiver architecture. The system was implemented using bulk optics and tested in a laboratory environment. A Delay Line Interferometer (DLI) was used for DPSK demodulation. The system successfully achieved a data rate of 100 [Mbit/s], demonstrating the feasibility of DPSK-based coherent free space detection. Some performance limitations were identified, with DLI instability emerging as the most notable, which is primarily caused by the long length required for this data rate. This instability resulted in intermittent bit error rate values exceeding the required threshold. These findings show that DPSK demodulation using bulk optics is favored toward higher data rates, and thus shorter delay lines. Recommendations for future work would be to operate at a higher data rate, and implement active stabilization for operational systems.
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As demand for high-bandwidth data transmission continues to increase, future satellite constellations can leverage the benefits of free space optical communication, which provides significant advantages compared to traditional radio frequency systems. Despite the development of satellite laser communication terminals (LCTs) in recent years, one major challenge remains; coupling the incoming signal into an optical fiber. In addition, most terminals use intensity modulation to encode data, which is limited in its ability to reach high data rates. So-called coherent modulation schemes offer superior performance but are not widely implemented in satellite LCT’s yet. A system that avoids fiber coupling while using coherent modulation could simplify designs, reduce complexity, and improve performance. This thesis presents the design, implementation, and evaluation of such a coherent free space optical detection system. Differential Phase Shift Keying (DPSK) was chosen as the modulation scheme due to its balance of power efficiency and implementation simplicity, delivering performance comparable to other coherent schemes with a less complex receiver architecture. The system was implemented using bulk optics and tested in a laboratory environment. A Delay Line Interferometer (DLI) was used for DPSK demodulation. The system successfully achieved a data rate of 100 [Mbit/s], demonstrating the feasibility of DPSK-based coherent free space detection. Some performance limitations were identified, with DLI instability emerging as the most notable, which is primarily caused by the long length required for this data rate. This instability resulted in intermittent bit error rate values exceeding the required threshold. These findings show that DPSK demodulation using bulk optics is favored toward higher data rates, and thus shorter delay lines. Recommendations for future work would be to operate at a higher data rate, and implement active stabilization for operational systems.
Contactless Coarse Pointing Assembly
Development of a Wireless Power and Synchronous Data Transfer Interface for Free Rotation and Zero Torque Laser Beam Handling
Laser satellite communication effectively addresses high data rates, low latency, high security and license-free operation of down to Earth and inter-satellite data links, crucial for the growing data demands in space amid radio frequency spectrum congestion. However, this approach presents challenges, notably in meeting micro-radian pointing accuracy of laser beams due to the low divergence nature of the high frequency optical wavelengths utilised. Laser communication terminals handle the strict pointing accuracy requirements by segmenting the pointing strategies into coarse and fine pointing mechanisms. The coarse pointing assembly (CPA), the focus of this research, provides large field of view, low bandwidth laser beam pointing with minimal static and dynamic pointing error. Common pointing budgets allocate errors up to 100-500 μrad for static pointing and 1-5 μrad for dynamic pointing biases during operation. The CPA operates on the simultaneous actuation of two axes, elevation and azimuth, to anticipate relative spacecraft motion for inter-satellite links and alternatively, to Earth based ground stations. For complete closed loop pointing of the CPA, the elevation axes power, motor control signals and sensor feedback needs to pass over the rotating azimuth axis. The state of the art mechanisms used to accomplish this are flex wraps, flexible PCBs coiled around a central axis, which unspools and retracts for azimuthal movements. However, flex wraps negatively impact CPA pointing performance through their material stiffness destabilisation torques, limit the CPA lifetime due to material fatigue characteristics, pose manufacturing and assembly complexity, inhibit fully continuous 360 degree pointing operation of the CPA, and restrict the instruments achievable slew rates. The development in this domain of CPA technology has remained largely stagnant for multiple years.
This research looks into the field of contactless technology to analyse, design and develop a novel wireless interface for the continuous rotation, low torque and high precision pointing of CPAs, by aiming to eliminate all wired connections between the rotation axes. The conceptual design, analysis implementation and manufacturing of a contactless interface concept was carried out through a 10 month period, bringing the technology from TRL 1 to TRL 4, concluding with the testing and demonstration of a fully synchronous wireless power and bi-directional data transmission interface for CPA applications. The system accomplished a DC-DC raw power transfer efficiency of 73% and a maximum full duplex symbol rate over the contactless link of 100 kbps. Therefore, the contactless CPA interface displays the ability for a miniaturised and fully integrated solution to wirelessly couple power over free space while simultaneously enabling data transfer over a single coil element independent of any rotation effects.
The test results of the manufactured contactless interface displayed promise for the future implementation in a CPA, the system enables the full, undisturbed, continuous rotation of the CPA during operation. Complete pointing performance testing was not performed, however it is hypothesised that the implementation of the system would eliminate line resistance and material stiffness hysteric effects, conceivably removing all flex wrap induced pointing destabilisations and providing zero wear operations, removing instrument lifetime restrictions. However In doing so, the power transfer efficiency and number of signal data lines suffer a reduction as compared to flex wraps. As a part of this research, space radiation and thermal effects were not assessed in detail, however their influence was found to impact the overall design direction and component choices. ...
This research looks into the field of contactless technology to analyse, design and develop a novel wireless interface for the continuous rotation, low torque and high precision pointing of CPAs, by aiming to eliminate all wired connections between the rotation axes. The conceptual design, analysis implementation and manufacturing of a contactless interface concept was carried out through a 10 month period, bringing the technology from TRL 1 to TRL 4, concluding with the testing and demonstration of a fully synchronous wireless power and bi-directional data transmission interface for CPA applications. The system accomplished a DC-DC raw power transfer efficiency of 73% and a maximum full duplex symbol rate over the contactless link of 100 kbps. Therefore, the contactless CPA interface displays the ability for a miniaturised and fully integrated solution to wirelessly couple power over free space while simultaneously enabling data transfer over a single coil element independent of any rotation effects.
The test results of the manufactured contactless interface displayed promise for the future implementation in a CPA, the system enables the full, undisturbed, continuous rotation of the CPA during operation. Complete pointing performance testing was not performed, however it is hypothesised that the implementation of the system would eliminate line resistance and material stiffness hysteric effects, conceivably removing all flex wrap induced pointing destabilisations and providing zero wear operations, removing instrument lifetime restrictions. However In doing so, the power transfer efficiency and number of signal data lines suffer a reduction as compared to flex wraps. As a part of this research, space radiation and thermal effects were not assessed in detail, however their influence was found to impact the overall design direction and component choices. ...
Laser satellite communication effectively addresses high data rates, low latency, high security and license-free operation of down to Earth and inter-satellite data links, crucial for the growing data demands in space amid radio frequency spectrum congestion. However, this approach presents challenges, notably in meeting micro-radian pointing accuracy of laser beams due to the low divergence nature of the high frequency optical wavelengths utilised. Laser communication terminals handle the strict pointing accuracy requirements by segmenting the pointing strategies into coarse and fine pointing mechanisms. The coarse pointing assembly (CPA), the focus of this research, provides large field of view, low bandwidth laser beam pointing with minimal static and dynamic pointing error. Common pointing budgets allocate errors up to 100-500 μrad for static pointing and 1-5 μrad for dynamic pointing biases during operation. The CPA operates on the simultaneous actuation of two axes, elevation and azimuth, to anticipate relative spacecraft motion for inter-satellite links and alternatively, to Earth based ground stations. For complete closed loop pointing of the CPA, the elevation axes power, motor control signals and sensor feedback needs to pass over the rotating azimuth axis. The state of the art mechanisms used to accomplish this are flex wraps, flexible PCBs coiled around a central axis, which unspools and retracts for azimuthal movements. However, flex wraps negatively impact CPA pointing performance through their material stiffness destabilisation torques, limit the CPA lifetime due to material fatigue characteristics, pose manufacturing and assembly complexity, inhibit fully continuous 360 degree pointing operation of the CPA, and restrict the instruments achievable slew rates. The development in this domain of CPA technology has remained largely stagnant for multiple years.
This research looks into the field of contactless technology to analyse, design and develop a novel wireless interface for the continuous rotation, low torque and high precision pointing of CPAs, by aiming to eliminate all wired connections between the rotation axes. The conceptual design, analysis implementation and manufacturing of a contactless interface concept was carried out through a 10 month period, bringing the technology from TRL 1 to TRL 4, concluding with the testing and demonstration of a fully synchronous wireless power and bi-directional data transmission interface for CPA applications. The system accomplished a DC-DC raw power transfer efficiency of 73% and a maximum full duplex symbol rate over the contactless link of 100 kbps. Therefore, the contactless CPA interface displays the ability for a miniaturised and fully integrated solution to wirelessly couple power over free space while simultaneously enabling data transfer over a single coil element independent of any rotation effects.
The test results of the manufactured contactless interface displayed promise for the future implementation in a CPA, the system enables the full, undisturbed, continuous rotation of the CPA during operation. Complete pointing performance testing was not performed, however it is hypothesised that the implementation of the system would eliminate line resistance and material stiffness hysteric effects, conceivably removing all flex wrap induced pointing destabilisations and providing zero wear operations, removing instrument lifetime restrictions. However In doing so, the power transfer efficiency and number of signal data lines suffer a reduction as compared to flex wraps. As a part of this research, space radiation and thermal effects were not assessed in detail, however their influence was found to impact the overall design direction and component choices.
This research looks into the field of contactless technology to analyse, design and develop a novel wireless interface for the continuous rotation, low torque and high precision pointing of CPAs, by aiming to eliminate all wired connections between the rotation axes. The conceptual design, analysis implementation and manufacturing of a contactless interface concept was carried out through a 10 month period, bringing the technology from TRL 1 to TRL 4, concluding with the testing and demonstration of a fully synchronous wireless power and bi-directional data transmission interface for CPA applications. The system accomplished a DC-DC raw power transfer efficiency of 73% and a maximum full duplex symbol rate over the contactless link of 100 kbps. Therefore, the contactless CPA interface displays the ability for a miniaturised and fully integrated solution to wirelessly couple power over free space while simultaneously enabling data transfer over a single coil element independent of any rotation effects.
The test results of the manufactured contactless interface displayed promise for the future implementation in a CPA, the system enables the full, undisturbed, continuous rotation of the CPA during operation. Complete pointing performance testing was not performed, however it is hypothesised that the implementation of the system would eliminate line resistance and material stiffness hysteric effects, conceivably removing all flex wrap induced pointing destabilisations and providing zero wear operations, removing instrument lifetime restrictions. However In doing so, the power transfer efficiency and number of signal data lines suffer a reduction as compared to flex wraps. As a part of this research, space radiation and thermal effects were not assessed in detail, however their influence was found to impact the overall design direction and component choices.
Naval Free Space Optical communications
A simulation & control design of optical terminals operated in naval environments
Wireless Optical Communication (WOC) has recently become a viable complementary technology in addition to existing Radio Frequency Communication (RFC). One of its critical advantages over existing RFC is its significant increase in carrier frequency, since “it is a well-known fact that an increase in carrier frequency increases the information-carrying capacity of a communication system” [24]. WOC has several critical advantages over existing RFC, namely tariff-free bandwidth allocation, low on-board power requirements, and improved channel security. Due to the rise in global tensions, the last advantage can prove a crucial asset for military applications.
There are also several critical challenges of WOC, namely its high dependence on stable atmospheric conditions. Recent advances in Vertical-Cavity Surface-Emitting Lasers (VCSELs), Avalanche Photodiodes (APDs), Adaptive Optics, Real-Time Control, Active Optics, etc., have all allowed the challenges of WOC to be addressed, increasing the feasibility of implementing such technology as a practical communication system. The application of WOC for Ground-to-Low-Earth-Orbit communication is referred to as Free Space Optical Communication (FSOC). This application remains the focus of this work.
To perform FSOC, 3 main elements are required; these include the transmitter, the transmission channel, and the receiver. The fundamental working principle of this technology is to modulate the information into an optical carrier, typically performed at the transmitter in simplex mode. As a section of the transmission channel passes through Earth’s atmosphere, this results in the introduction of disturbances due to the presence of turbulence in the different layers of Earth’s atmosphere.
Therefore, a functional FSOC system must possess precise and efficient pointing capabilities at both receiver and transmitter ends, such that the communication channel has the capacity to compensate for the atmospheric disturbances. Therefore, the Pointing Acquisition and Tracking (PAT) system must comply with stringent angular and angular-rate pointing requirements.
While there is plenty of contemporary research regarding the design and testing of ground-based Optical Communications Terminals (OCTs) meant for FSOC, currently, there is a gap in knowledge regarding mobile OCTs. Therefore, the focus of this work has centered on the expansion of knowledge by investigating the achievable performance of a mobile OCT placed on board a Royal Netherlands Navy frigate-sized ship. To summarize, this thesis has centered on answering: What is the strategy to simulate and control the effects that ship-wave disturbances have on a mobile Dual-Stage Optical Communications Terminal to determine if the achievable pointing precision is sufficient for performing Free Space Optical Communications in naval environments?
To answer this, a simulation strategy has been employed to divide the work required to answer this question into 3 main steps. Besides this strategy, literature research has been performed to determine suitable system and sub-system requirements in close cooperation with the customer and research partner, the Royal Netherlands Air Force (Koninklijke Luchtmacht). The 3 key requirements are as follows:
PATR-01: The total angular (static) and angular-rate (dynamic) Root Mean Square (RMS) pointing jitter error shall not exceed 50 [μrad] / [μrad/sec]. PATR-01-01: The precise pointing actuator model shall approximate the dynamics and performance characteristics of the Optics in Motion OIM5001 Fast Steering Mirror (FSM). PATR-01-02: The coarse actuator model shall approximate the dynamics and performance characteristics of the PlaneWave Instruments L-350 direct-drive telescope mount.
The first step regarding the implementation of the simulation strategy has been the incorporation of the recordings from an inertial measurement system (sampling rate of 200 Hz) on board a Royal Netherlands Navy frigate-sized ship into the performance analysis. These measurements provide the angular and angular-rate disturbances, which the dual-stage communications terminal would require to compensate for. These disturbances are of a stochastic nature, since, as of writing, there are limited time-based simulation tools that can accept signals/disturbances of a stochastic nature. The decision was made to perform the analysis in the frequency spectrum, where the disturbance signals are represented as Power Spectral Density (PSD) functions.
The second step involved the development of a simulation that is capable of approximating the performance characteristics of a dual-stage mobile OCT. To complete this step, the focus centered on creating 3 separate simulation models, each allowing for the expansion of the capabilities of the previous models. These include the Precise Pointing Actuator System (PPAS), which centered on recreating the closed-loop system dynamics of the FSM OIM5001 as an LTI spring-damper system, paired with a PID controller and a Quadcell Photodiode (QPD) tracking sensor sampling delay. The QPD tracking sensor errors are included in the analysis in the form of an additional PSD disturbance signal.
The Coarse Pointing Actuator System (CPS) centered on modeling the L-350 gimbal telescope mount as an LTI spring-damper system, paired with a PI controller and the same QPD sampling delay. Lastly, the 3rd model (DSAS) centered on combining the previous models into a combined dual-stage chief-deputy controller configuration, where the chief stage (PPAS) is being actively off-loaded by the deputy stage (CPAS).
The last step of the simulation strategy has been the determination of the achievable performance of the 3 simulation models. To achieve this, the Dynamic Error Budgeting (DEB) design analysis has been utilized, as it allows for the determination of the performance of a system to which stochastic disturbance signals are applied.
From the performance results, it is possible to argue that individual actuator stages are unsuitable for FSOC in naval environments. While the performance results of the PPAS simulation model result in pointing angle and angle-rate errors of ≈ 24.6% and ≈ 43.6% below PATR-01, the angular range requirements go beyond those achievable by the FSM actuator, standing at ≈ ±9.06 degrees, while the actuator specification states a maximum range of ±3 degrees [38].
While the performance results of the CPAS indicated achievable actuator effort and controller torque requirements, the system is incapable of complying with the pointing requirements, remaining ≈ 234.6% above the allowable pointing angle error requirement and ≈ 234.6% above the allowable pointing angle-rate error.
With an understanding of the performance limitations of individual stages, it is now possible to motivate the need for a dual-stage optical communications system. Therefore, it is now relevant to discuss the performance results of the DSAS, which are comprised of multiple controller bandwidth configurations. Notable from these results are the highest-performance configurations with chief and deputy controller configurations of 398/500 Hz and 765/500 Hz. Both of these are capable of complying with the pointing requirements, each remaining ≈ 5.5% and ≈ 46.3% below the pointing angle rate, while both achieving to remain > 90% under the pointing angle requirement. At the highest two performance configurations, it can be seen that the deputy controller requires ≈ 12 N·m and has a power consumption of ≈ 94 W, which is an increase from the base configuration of ≈ 66.2% and ≈ 412.8%, respectively, both still falling within the actuator specifications. Another relevant outcome is the significant reduction in angular range requirements of the chief actuator, where for the highest performance configurations it is only required to provide 1.2–1.4 mdegrees of range.
With the DSAS performance results, it is of relevance to verify and back up such findings. To this end, 3 verification steps have been performed. The first step involved the demonstration of the correct functioning of the frequency analysis; this has been obtained by passing a test signal with known properties through the entire frequency analysis pipeline. It was then possible to determine that the estimated properties differ from their original properties by only an average of 2%. The second step involved verifying the control design of the DSAS. To achieve this, the transfer functions developed under this work were compared against equivalent transfer functions from research papers, which were found to be equivalent to each other. The last step involved verifying the performance results obtained from the DEB design approach. To achieve this, an alternative time-analysis simulation has been utilized to reproduce the performance results. The difference between the results obtained from the alternative simulation methods and DEB analysis remains at a margin of 1.3–2.8%.
In conclusion, it is possible to argue that a Dual-Stage optical communications terminal with a chief-deputy controller configuration of 398/500 Hz or 765/500 Hz can be capable of performing FSOC in naval environments by fulfilling PATR-01 pointing requirements and PATR-01-01, PATR-01-02 actuator specification sub-requirements, with a preference for the higher-bandwidth configuration. Regarding future work, it is possible to recommend extending the sampling frequency to 10–20 kHz for the inertial measurements, as this could allow the recreation of phenomena that could be occurring at higher frequencies. Another crucial recommendation would be the expansion of the simulation models into specific models obtained from system identification, as these could potentially improve the estimates regarding torque and power requirements of the deputy stage of the DSAS, which has been approximated via simple geometry.
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There are also several critical challenges of WOC, namely its high dependence on stable atmospheric conditions. Recent advances in Vertical-Cavity Surface-Emitting Lasers (VCSELs), Avalanche Photodiodes (APDs), Adaptive Optics, Real-Time Control, Active Optics, etc., have all allowed the challenges of WOC to be addressed, increasing the feasibility of implementing such technology as a practical communication system. The application of WOC for Ground-to-Low-Earth-Orbit communication is referred to as Free Space Optical Communication (FSOC). This application remains the focus of this work.
To perform FSOC, 3 main elements are required; these include the transmitter, the transmission channel, and the receiver. The fundamental working principle of this technology is to modulate the information into an optical carrier, typically performed at the transmitter in simplex mode. As a section of the transmission channel passes through Earth’s atmosphere, this results in the introduction of disturbances due to the presence of turbulence in the different layers of Earth’s atmosphere.
Therefore, a functional FSOC system must possess precise and efficient pointing capabilities at both receiver and transmitter ends, such that the communication channel has the capacity to compensate for the atmospheric disturbances. Therefore, the Pointing Acquisition and Tracking (PAT) system must comply with stringent angular and angular-rate pointing requirements.
While there is plenty of contemporary research regarding the design and testing of ground-based Optical Communications Terminals (OCTs) meant for FSOC, currently, there is a gap in knowledge regarding mobile OCTs. Therefore, the focus of this work has centered on the expansion of knowledge by investigating the achievable performance of a mobile OCT placed on board a Royal Netherlands Navy frigate-sized ship. To summarize, this thesis has centered on answering: What is the strategy to simulate and control the effects that ship-wave disturbances have on a mobile Dual-Stage Optical Communications Terminal to determine if the achievable pointing precision is sufficient for performing Free Space Optical Communications in naval environments?
To answer this, a simulation strategy has been employed to divide the work required to answer this question into 3 main steps. Besides this strategy, literature research has been performed to determine suitable system and sub-system requirements in close cooperation with the customer and research partner, the Royal Netherlands Air Force (Koninklijke Luchtmacht). The 3 key requirements are as follows:
PATR-01: The total angular (static) and angular-rate (dynamic) Root Mean Square (RMS) pointing jitter error shall not exceed 50 [μrad] / [μrad/sec]. PATR-01-01: The precise pointing actuator model shall approximate the dynamics and performance characteristics of the Optics in Motion OIM5001 Fast Steering Mirror (FSM). PATR-01-02: The coarse actuator model shall approximate the dynamics and performance characteristics of the PlaneWave Instruments L-350 direct-drive telescope mount.
The first step regarding the implementation of the simulation strategy has been the incorporation of the recordings from an inertial measurement system (sampling rate of 200 Hz) on board a Royal Netherlands Navy frigate-sized ship into the performance analysis. These measurements provide the angular and angular-rate disturbances, which the dual-stage communications terminal would require to compensate for. These disturbances are of a stochastic nature, since, as of writing, there are limited time-based simulation tools that can accept signals/disturbances of a stochastic nature. The decision was made to perform the analysis in the frequency spectrum, where the disturbance signals are represented as Power Spectral Density (PSD) functions.
The second step involved the development of a simulation that is capable of approximating the performance characteristics of a dual-stage mobile OCT. To complete this step, the focus centered on creating 3 separate simulation models, each allowing for the expansion of the capabilities of the previous models. These include the Precise Pointing Actuator System (PPAS), which centered on recreating the closed-loop system dynamics of the FSM OIM5001 as an LTI spring-damper system, paired with a PID controller and a Quadcell Photodiode (QPD) tracking sensor sampling delay. The QPD tracking sensor errors are included in the analysis in the form of an additional PSD disturbance signal.
The Coarse Pointing Actuator System (CPS) centered on modeling the L-350 gimbal telescope mount as an LTI spring-damper system, paired with a PI controller and the same QPD sampling delay. Lastly, the 3rd model (DSAS) centered on combining the previous models into a combined dual-stage chief-deputy controller configuration, where the chief stage (PPAS) is being actively off-loaded by the deputy stage (CPAS).
The last step of the simulation strategy has been the determination of the achievable performance of the 3 simulation models. To achieve this, the Dynamic Error Budgeting (DEB) design analysis has been utilized, as it allows for the determination of the performance of a system to which stochastic disturbance signals are applied.
From the performance results, it is possible to argue that individual actuator stages are unsuitable for FSOC in naval environments. While the performance results of the PPAS simulation model result in pointing angle and angle-rate errors of ≈ 24.6% and ≈ 43.6% below PATR-01, the angular range requirements go beyond those achievable by the FSM actuator, standing at ≈ ±9.06 degrees, while the actuator specification states a maximum range of ±3 degrees [38].
While the performance results of the CPAS indicated achievable actuator effort and controller torque requirements, the system is incapable of complying with the pointing requirements, remaining ≈ 234.6% above the allowable pointing angle error requirement and ≈ 234.6% above the allowable pointing angle-rate error.
With an understanding of the performance limitations of individual stages, it is now possible to motivate the need for a dual-stage optical communications system. Therefore, it is now relevant to discuss the performance results of the DSAS, which are comprised of multiple controller bandwidth configurations. Notable from these results are the highest-performance configurations with chief and deputy controller configurations of 398/500 Hz and 765/500 Hz. Both of these are capable of complying with the pointing requirements, each remaining ≈ 5.5% and ≈ 46.3% below the pointing angle rate, while both achieving to remain > 90% under the pointing angle requirement. At the highest two performance configurations, it can be seen that the deputy controller requires ≈ 12 N·m and has a power consumption of ≈ 94 W, which is an increase from the base configuration of ≈ 66.2% and ≈ 412.8%, respectively, both still falling within the actuator specifications. Another relevant outcome is the significant reduction in angular range requirements of the chief actuator, where for the highest performance configurations it is only required to provide 1.2–1.4 mdegrees of range.
With the DSAS performance results, it is of relevance to verify and back up such findings. To this end, 3 verification steps have been performed. The first step involved the demonstration of the correct functioning of the frequency analysis; this has been obtained by passing a test signal with known properties through the entire frequency analysis pipeline. It was then possible to determine that the estimated properties differ from their original properties by only an average of 2%. The second step involved verifying the control design of the DSAS. To achieve this, the transfer functions developed under this work were compared against equivalent transfer functions from research papers, which were found to be equivalent to each other. The last step involved verifying the performance results obtained from the DEB design approach. To achieve this, an alternative time-analysis simulation has been utilized to reproduce the performance results. The difference between the results obtained from the alternative simulation methods and DEB analysis remains at a margin of 1.3–2.8%.
In conclusion, it is possible to argue that a Dual-Stage optical communications terminal with a chief-deputy controller configuration of 398/500 Hz or 765/500 Hz can be capable of performing FSOC in naval environments by fulfilling PATR-01 pointing requirements and PATR-01-01, PATR-01-02 actuator specification sub-requirements, with a preference for the higher-bandwidth configuration. Regarding future work, it is possible to recommend extending the sampling frequency to 10–20 kHz for the inertial measurements, as this could allow the recreation of phenomena that could be occurring at higher frequencies. Another crucial recommendation would be the expansion of the simulation models into specific models obtained from system identification, as these could potentially improve the estimates regarding torque and power requirements of the deputy stage of the DSAS, which has been approximated via simple geometry.
...
Wireless Optical Communication (WOC) has recently become a viable complementary technology in addition to existing Radio Frequency Communication (RFC). One of its critical advantages over existing RFC is its significant increase in carrier frequency, since “it is a well-known fact that an increase in carrier frequency increases the information-carrying capacity of a communication system” [24]. WOC has several critical advantages over existing RFC, namely tariff-free bandwidth allocation, low on-board power requirements, and improved channel security. Due to the rise in global tensions, the last advantage can prove a crucial asset for military applications.
There are also several critical challenges of WOC, namely its high dependence on stable atmospheric conditions. Recent advances in Vertical-Cavity Surface-Emitting Lasers (VCSELs), Avalanche Photodiodes (APDs), Adaptive Optics, Real-Time Control, Active Optics, etc., have all allowed the challenges of WOC to be addressed, increasing the feasibility of implementing such technology as a practical communication system. The application of WOC for Ground-to-Low-Earth-Orbit communication is referred to as Free Space Optical Communication (FSOC). This application remains the focus of this work.
To perform FSOC, 3 main elements are required; these include the transmitter, the transmission channel, and the receiver. The fundamental working principle of this technology is to modulate the information into an optical carrier, typically performed at the transmitter in simplex mode. As a section of the transmission channel passes through Earth’s atmosphere, this results in the introduction of disturbances due to the presence of turbulence in the different layers of Earth’s atmosphere.
Therefore, a functional FSOC system must possess precise and efficient pointing capabilities at both receiver and transmitter ends, such that the communication channel has the capacity to compensate for the atmospheric disturbances. Therefore, the Pointing Acquisition and Tracking (PAT) system must comply with stringent angular and angular-rate pointing requirements.
While there is plenty of contemporary research regarding the design and testing of ground-based Optical Communications Terminals (OCTs) meant for FSOC, currently, there is a gap in knowledge regarding mobile OCTs. Therefore, the focus of this work has centered on the expansion of knowledge by investigating the achievable performance of a mobile OCT placed on board a Royal Netherlands Navy frigate-sized ship. To summarize, this thesis has centered on answering: What is the strategy to simulate and control the effects that ship-wave disturbances have on a mobile Dual-Stage Optical Communications Terminal to determine if the achievable pointing precision is sufficient for performing Free Space Optical Communications in naval environments?
To answer this, a simulation strategy has been employed to divide the work required to answer this question into 3 main steps. Besides this strategy, literature research has been performed to determine suitable system and sub-system requirements in close cooperation with the customer and research partner, the Royal Netherlands Air Force (Koninklijke Luchtmacht). The 3 key requirements are as follows:
PATR-01: The total angular (static) and angular-rate (dynamic) Root Mean Square (RMS) pointing jitter error shall not exceed 50 [μrad] / [μrad/sec]. PATR-01-01: The precise pointing actuator model shall approximate the dynamics and performance characteristics of the Optics in Motion OIM5001 Fast Steering Mirror (FSM). PATR-01-02: The coarse actuator model shall approximate the dynamics and performance characteristics of the PlaneWave Instruments L-350 direct-drive telescope mount.
The first step regarding the implementation of the simulation strategy has been the incorporation of the recordings from an inertial measurement system (sampling rate of 200 Hz) on board a Royal Netherlands Navy frigate-sized ship into the performance analysis. These measurements provide the angular and angular-rate disturbances, which the dual-stage communications terminal would require to compensate for. These disturbances are of a stochastic nature, since, as of writing, there are limited time-based simulation tools that can accept signals/disturbances of a stochastic nature. The decision was made to perform the analysis in the frequency spectrum, where the disturbance signals are represented as Power Spectral Density (PSD) functions.
The second step involved the development of a simulation that is capable of approximating the performance characteristics of a dual-stage mobile OCT. To complete this step, the focus centered on creating 3 separate simulation models, each allowing for the expansion of the capabilities of the previous models. These include the Precise Pointing Actuator System (PPAS), which centered on recreating the closed-loop system dynamics of the FSM OIM5001 as an LTI spring-damper system, paired with a PID controller and a Quadcell Photodiode (QPD) tracking sensor sampling delay. The QPD tracking sensor errors are included in the analysis in the form of an additional PSD disturbance signal.
The Coarse Pointing Actuator System (CPS) centered on modeling the L-350 gimbal telescope mount as an LTI spring-damper system, paired with a PI controller and the same QPD sampling delay. Lastly, the 3rd model (DSAS) centered on combining the previous models into a combined dual-stage chief-deputy controller configuration, where the chief stage (PPAS) is being actively off-loaded by the deputy stage (CPAS).
The last step of the simulation strategy has been the determination of the achievable performance of the 3 simulation models. To achieve this, the Dynamic Error Budgeting (DEB) design analysis has been utilized, as it allows for the determination of the performance of a system to which stochastic disturbance signals are applied.
From the performance results, it is possible to argue that individual actuator stages are unsuitable for FSOC in naval environments. While the performance results of the PPAS simulation model result in pointing angle and angle-rate errors of ≈ 24.6% and ≈ 43.6% below PATR-01, the angular range requirements go beyond those achievable by the FSM actuator, standing at ≈ ±9.06 degrees, while the actuator specification states a maximum range of ±3 degrees [38].
While the performance results of the CPAS indicated achievable actuator effort and controller torque requirements, the system is incapable of complying with the pointing requirements, remaining ≈ 234.6% above the allowable pointing angle error requirement and ≈ 234.6% above the allowable pointing angle-rate error.
With an understanding of the performance limitations of individual stages, it is now possible to motivate the need for a dual-stage optical communications system. Therefore, it is now relevant to discuss the performance results of the DSAS, which are comprised of multiple controller bandwidth configurations. Notable from these results are the highest-performance configurations with chief and deputy controller configurations of 398/500 Hz and 765/500 Hz. Both of these are capable of complying with the pointing requirements, each remaining ≈ 5.5% and ≈ 46.3% below the pointing angle rate, while both achieving to remain > 90% under the pointing angle requirement. At the highest two performance configurations, it can be seen that the deputy controller requires ≈ 12 N·m and has a power consumption of ≈ 94 W, which is an increase from the base configuration of ≈ 66.2% and ≈ 412.8%, respectively, both still falling within the actuator specifications. Another relevant outcome is the significant reduction in angular range requirements of the chief actuator, where for the highest performance configurations it is only required to provide 1.2–1.4 mdegrees of range.
With the DSAS performance results, it is of relevance to verify and back up such findings. To this end, 3 verification steps have been performed. The first step involved the demonstration of the correct functioning of the frequency analysis; this has been obtained by passing a test signal with known properties through the entire frequency analysis pipeline. It was then possible to determine that the estimated properties differ from their original properties by only an average of 2%. The second step involved verifying the control design of the DSAS. To achieve this, the transfer functions developed under this work were compared against equivalent transfer functions from research papers, which were found to be equivalent to each other. The last step involved verifying the performance results obtained from the DEB design approach. To achieve this, an alternative time-analysis simulation has been utilized to reproduce the performance results. The difference between the results obtained from the alternative simulation methods and DEB analysis remains at a margin of 1.3–2.8%.
In conclusion, it is possible to argue that a Dual-Stage optical communications terminal with a chief-deputy controller configuration of 398/500 Hz or 765/500 Hz can be capable of performing FSOC in naval environments by fulfilling PATR-01 pointing requirements and PATR-01-01, PATR-01-02 actuator specification sub-requirements, with a preference for the higher-bandwidth configuration. Regarding future work, it is possible to recommend extending the sampling frequency to 10–20 kHz for the inertial measurements, as this could allow the recreation of phenomena that could be occurring at higher frequencies. Another crucial recommendation would be the expansion of the simulation models into specific models obtained from system identification, as these could potentially improve the estimates regarding torque and power requirements of the deputy stage of the DSAS, which has been approximated via simple geometry.
There are also several critical challenges of WOC, namely its high dependence on stable atmospheric conditions. Recent advances in Vertical-Cavity Surface-Emitting Lasers (VCSELs), Avalanche Photodiodes (APDs), Adaptive Optics, Real-Time Control, Active Optics, etc., have all allowed the challenges of WOC to be addressed, increasing the feasibility of implementing such technology as a practical communication system. The application of WOC for Ground-to-Low-Earth-Orbit communication is referred to as Free Space Optical Communication (FSOC). This application remains the focus of this work.
To perform FSOC, 3 main elements are required; these include the transmitter, the transmission channel, and the receiver. The fundamental working principle of this technology is to modulate the information into an optical carrier, typically performed at the transmitter in simplex mode. As a section of the transmission channel passes through Earth’s atmosphere, this results in the introduction of disturbances due to the presence of turbulence in the different layers of Earth’s atmosphere.
Therefore, a functional FSOC system must possess precise and efficient pointing capabilities at both receiver and transmitter ends, such that the communication channel has the capacity to compensate for the atmospheric disturbances. Therefore, the Pointing Acquisition and Tracking (PAT) system must comply with stringent angular and angular-rate pointing requirements.
While there is plenty of contemporary research regarding the design and testing of ground-based Optical Communications Terminals (OCTs) meant for FSOC, currently, there is a gap in knowledge regarding mobile OCTs. Therefore, the focus of this work has centered on the expansion of knowledge by investigating the achievable performance of a mobile OCT placed on board a Royal Netherlands Navy frigate-sized ship. To summarize, this thesis has centered on answering: What is the strategy to simulate and control the effects that ship-wave disturbances have on a mobile Dual-Stage Optical Communications Terminal to determine if the achievable pointing precision is sufficient for performing Free Space Optical Communications in naval environments?
To answer this, a simulation strategy has been employed to divide the work required to answer this question into 3 main steps. Besides this strategy, literature research has been performed to determine suitable system and sub-system requirements in close cooperation with the customer and research partner, the Royal Netherlands Air Force (Koninklijke Luchtmacht). The 3 key requirements are as follows:
PATR-01: The total angular (static) and angular-rate (dynamic) Root Mean Square (RMS) pointing jitter error shall not exceed 50 [μrad] / [μrad/sec]. PATR-01-01: The precise pointing actuator model shall approximate the dynamics and performance characteristics of the Optics in Motion OIM5001 Fast Steering Mirror (FSM). PATR-01-02: The coarse actuator model shall approximate the dynamics and performance characteristics of the PlaneWave Instruments L-350 direct-drive telescope mount.
The first step regarding the implementation of the simulation strategy has been the incorporation of the recordings from an inertial measurement system (sampling rate of 200 Hz) on board a Royal Netherlands Navy frigate-sized ship into the performance analysis. These measurements provide the angular and angular-rate disturbances, which the dual-stage communications terminal would require to compensate for. These disturbances are of a stochastic nature, since, as of writing, there are limited time-based simulation tools that can accept signals/disturbances of a stochastic nature. The decision was made to perform the analysis in the frequency spectrum, where the disturbance signals are represented as Power Spectral Density (PSD) functions.
The second step involved the development of a simulation that is capable of approximating the performance characteristics of a dual-stage mobile OCT. To complete this step, the focus centered on creating 3 separate simulation models, each allowing for the expansion of the capabilities of the previous models. These include the Precise Pointing Actuator System (PPAS), which centered on recreating the closed-loop system dynamics of the FSM OIM5001 as an LTI spring-damper system, paired with a PID controller and a Quadcell Photodiode (QPD) tracking sensor sampling delay. The QPD tracking sensor errors are included in the analysis in the form of an additional PSD disturbance signal.
The Coarse Pointing Actuator System (CPS) centered on modeling the L-350 gimbal telescope mount as an LTI spring-damper system, paired with a PI controller and the same QPD sampling delay. Lastly, the 3rd model (DSAS) centered on combining the previous models into a combined dual-stage chief-deputy controller configuration, where the chief stage (PPAS) is being actively off-loaded by the deputy stage (CPAS).
The last step of the simulation strategy has been the determination of the achievable performance of the 3 simulation models. To achieve this, the Dynamic Error Budgeting (DEB) design analysis has been utilized, as it allows for the determination of the performance of a system to which stochastic disturbance signals are applied.
From the performance results, it is possible to argue that individual actuator stages are unsuitable for FSOC in naval environments. While the performance results of the PPAS simulation model result in pointing angle and angle-rate errors of ≈ 24.6% and ≈ 43.6% below PATR-01, the angular range requirements go beyond those achievable by the FSM actuator, standing at ≈ ±9.06 degrees, while the actuator specification states a maximum range of ±3 degrees [38].
While the performance results of the CPAS indicated achievable actuator effort and controller torque requirements, the system is incapable of complying with the pointing requirements, remaining ≈ 234.6% above the allowable pointing angle error requirement and ≈ 234.6% above the allowable pointing angle-rate error.
With an understanding of the performance limitations of individual stages, it is now possible to motivate the need for a dual-stage optical communications system. Therefore, it is now relevant to discuss the performance results of the DSAS, which are comprised of multiple controller bandwidth configurations. Notable from these results are the highest-performance configurations with chief and deputy controller configurations of 398/500 Hz and 765/500 Hz. Both of these are capable of complying with the pointing requirements, each remaining ≈ 5.5% and ≈ 46.3% below the pointing angle rate, while both achieving to remain > 90% under the pointing angle requirement. At the highest two performance configurations, it can be seen that the deputy controller requires ≈ 12 N·m and has a power consumption of ≈ 94 W, which is an increase from the base configuration of ≈ 66.2% and ≈ 412.8%, respectively, both still falling within the actuator specifications. Another relevant outcome is the significant reduction in angular range requirements of the chief actuator, where for the highest performance configurations it is only required to provide 1.2–1.4 mdegrees of range.
With the DSAS performance results, it is of relevance to verify and back up such findings. To this end, 3 verification steps have been performed. The first step involved the demonstration of the correct functioning of the frequency analysis; this has been obtained by passing a test signal with known properties through the entire frequency analysis pipeline. It was then possible to determine that the estimated properties differ from their original properties by only an average of 2%. The second step involved verifying the control design of the DSAS. To achieve this, the transfer functions developed under this work were compared against equivalent transfer functions from research papers, which were found to be equivalent to each other. The last step involved verifying the performance results obtained from the DEB design approach. To achieve this, an alternative time-analysis simulation has been utilized to reproduce the performance results. The difference between the results obtained from the alternative simulation methods and DEB analysis remains at a margin of 1.3–2.8%.
In conclusion, it is possible to argue that a Dual-Stage optical communications terminal with a chief-deputy controller configuration of 398/500 Hz or 765/500 Hz can be capable of performing FSOC in naval environments by fulfilling PATR-01 pointing requirements and PATR-01-01, PATR-01-02 actuator specification sub-requirements, with a preference for the higher-bandwidth configuration. Regarding future work, it is possible to recommend extending the sampling frequency to 10–20 kHz for the inertial measurements, as this could allow the recreation of phenomena that could be occurring at higher frequencies. Another crucial recommendation would be the expansion of the simulation models into specific models obtained from system identification, as these could potentially improve the estimates regarding torque and power requirements of the deputy stage of the DSAS, which has been approximated via simple geometry.
Fine Pointing Assembly for Optical Ground Station
Tip-Tilt removal through feedback control
The mini optical ground station (MISO), on top of the Aerospace Engineering faculty, serves the purpose of demonstrating Free Space Optical Communication technology. A downlink from low earth orbit imposes pointing requirements beyond what can be achieved by the telescope mount. A Fine Pointing Assembly (FPA), the topic of this thesis, aims to reduce residual pointing error to facilitate coupling into a single-mode fiber architecture. This thesis addresses the design, implementation, and characterization of FPA to fulfill this job in a lab environment. The FPA was built as a feedback control system actuating a fine steering mirror to counteract tip-tilt with feedback from a SWIR camera and the center of the gravity tracking algorithm. The bandwidth of this system is limited by latency from software implementations of the interfaces. The developed FPA removes 76% of the Tip-Tilt disturbance energy and can be improved by mitigation efforts toward latency reduction.
...
The mini optical ground station (MISO), on top of the Aerospace Engineering faculty, serves the purpose of demonstrating Free Space Optical Communication technology. A downlink from low earth orbit imposes pointing requirements beyond what can be achieved by the telescope mount. A Fine Pointing Assembly (FPA), the topic of this thesis, aims to reduce residual pointing error to facilitate coupling into a single-mode fiber architecture. This thesis addresses the design, implementation, and characterization of FPA to fulfill this job in a lab environment. The FPA was built as a feedback control system actuating a fine steering mirror to counteract tip-tilt with feedback from a SWIR camera and the center of the gravity tracking algorithm. The bandwidth of this system is limited by latency from software implementations of the interfaces. The developed FPA removes 76% of the Tip-Tilt disturbance energy and can be improved by mitigation efforts toward latency reduction.
Future Very High-Throughput Satellites are foreseen to implement optical ground-to-satellite feeder links to achieve multi-terabit-per-second data rates. Optical links however, are highly susceptible to atmospheric losses caused by turbulence, absorption, and scattering, especially at low elevation angles. Despite prior confirmation of the feasibility of cloud-free network availability, high-latitude stations have been notably absent from optical feeder link studies due to the limitation of Geostationary orbits in providing sufficiently high link elevation angles. Tundra orbits present a promising alternative to Geostationary orbit, requiring two satellites to ensure uninterrupted coverage of high-latitude regions like Europe and Canada with link geometries highly suitable for optical communication. This paper addresses optical feeder link implementation aspects in Tundra orbits and selects a suitable orbit to service Canada while considering aspects such as coverage, radiation environment, pointing angles, and delta-v impact. End-to-end simulations, including downlink and uplink amplitude statistics, are presented to assess dynamic turbulence penalties. These simulations focus on angular anisoplanatism and highlight the link geometry impact on adaptive optics efficacy. This analysis anticipates a mean 4.1 and 4.7 dBm link budget advantage for Tundra configurations for two and three satellites respectively. These findings highlight Tundra constellations' potential to enhance satellite communication infrastructure, providing robust, efficient service in regions where Geostationary orbits faces limitations.
...
Future Very High-Throughput Satellites are foreseen to implement optical ground-to-satellite feeder links to achieve multi-terabit-per-second data rates. Optical links however, are highly susceptible to atmospheric losses caused by turbulence, absorption, and scattering, especially at low elevation angles. Despite prior confirmation of the feasibility of cloud-free network availability, high-latitude stations have been notably absent from optical feeder link studies due to the limitation of Geostationary orbits in providing sufficiently high link elevation angles. Tundra orbits present a promising alternative to Geostationary orbit, requiring two satellites to ensure uninterrupted coverage of high-latitude regions like Europe and Canada with link geometries highly suitable for optical communication. This paper addresses optical feeder link implementation aspects in Tundra orbits and selects a suitable orbit to service Canada while considering aspects such as coverage, radiation environment, pointing angles, and delta-v impact. End-to-end simulations, including downlink and uplink amplitude statistics, are presented to assess dynamic turbulence penalties. These simulations focus on angular anisoplanatism and highlight the link geometry impact on adaptive optics efficacy. This analysis anticipates a mean 4.1 and 4.7 dBm link budget advantage for Tundra configurations for two and three satellites respectively. These findings highlight Tundra constellations' potential to enhance satellite communication infrastructure, providing robust, efficient service in regions where Geostationary orbits faces limitations.
Master thesis
(2024)
-
V. Affatato, S.J.M. Dr Potin, R. Saathof, J.J.D. Loicq, M.S. Uludag, Matthias Grott, Christian Althaus
Since their first use during the Apollo 15, 16, and 17 missions, laser altimeters have become indispensable for planetary exploration, enabling topographic mapping of rocky bodies throughout the solar system. The latest European contributions in this field are represented by the BepiColombo Laser Altimeter (BELA) and the Ganymede Laser Altimeter (GALA), developed by the DLR Institute of Planetary Research and currently en route to Mercury and the Jovian moons, respectively. However, to date, such instruments have only been deployed on large satellites, failing to meet miniaturised systems' SWaP (Size, Weight, and Power) requirements.
This thesis investigates the adaptation of laser altimeter technology for smaller platforms, focusing on the NLA (New Laser Altimeter) developed for the SER3NE (Selene's Explorer for Roughness, Regolith, Resources, Neutrons, and Elements) mission proposal. The instrument aims to improve the precision of Lunar topographic data to support the characterisation of future landing sites for crewed missions from a 12 U microsatellite. To meet the stringent SWaP constraints, the design will feature a transceiver and a single-photon detection system — an approach never previously applied to topographic altimeters.
This thesis aims to develop an optical design that fits the instrument within a 3 U volume. Given the innovative nature of the design, a trade-off analysis was conducted to evaluate several configurations based on their compactness, cross-coupling between the laser source and detector, footprint size at the target, co-alignment between the transmitter and receiver, and transmission losses. The selected design stood out in providing a footprint size in the range allowed by the requirements, reducing the probability of damage to the detector due to internal reflections from the laser, and guaranteeing a more stable co-alignment between the transmitter and receiver paths. It includes a transmitter with two 45° folding mirrors, a borehole mirror that allows the laser to pass while deflecting the returning signal, and a shared telescope.
A test campaign is then conducted on a dedicated optomechanical design to assess 1) its compliance with some trade-off criteria and 2) its functionality. The expansion performance is demonstrated as predictable and reliable, guaranteeing the desired divergence and footprint at the target. On the other hand, the transmittance is increased above the constraints by varying the angle of incidence of the light on the band-pass filter. For the functional tests, the quality of the wavefront is first evaluated, resulting in an aberration-free transmitter and a slightly worse receiver, but still acceptable for altimetry applications. Finally, the prototype is aligned thoroughly and tested for timing measurements with single-pixel detectors, successfully providing the range to the target.
In the next instrument development phase, throughout the pre-phase A studies in collaboration with ESA (European Space Agency) and relevant companies, the prototype will be enhanced to verify the performance in the other criteria and test its functionality in a relevant environment with a flight campaign. ...
This thesis investigates the adaptation of laser altimeter technology for smaller platforms, focusing on the NLA (New Laser Altimeter) developed for the SER3NE (Selene's Explorer for Roughness, Regolith, Resources, Neutrons, and Elements) mission proposal. The instrument aims to improve the precision of Lunar topographic data to support the characterisation of future landing sites for crewed missions from a 12 U microsatellite. To meet the stringent SWaP constraints, the design will feature a transceiver and a single-photon detection system — an approach never previously applied to topographic altimeters.
This thesis aims to develop an optical design that fits the instrument within a 3 U volume. Given the innovative nature of the design, a trade-off analysis was conducted to evaluate several configurations based on their compactness, cross-coupling between the laser source and detector, footprint size at the target, co-alignment between the transmitter and receiver, and transmission losses. The selected design stood out in providing a footprint size in the range allowed by the requirements, reducing the probability of damage to the detector due to internal reflections from the laser, and guaranteeing a more stable co-alignment between the transmitter and receiver paths. It includes a transmitter with two 45° folding mirrors, a borehole mirror that allows the laser to pass while deflecting the returning signal, and a shared telescope.
A test campaign is then conducted on a dedicated optomechanical design to assess 1) its compliance with some trade-off criteria and 2) its functionality. The expansion performance is demonstrated as predictable and reliable, guaranteeing the desired divergence and footprint at the target. On the other hand, the transmittance is increased above the constraints by varying the angle of incidence of the light on the band-pass filter. For the functional tests, the quality of the wavefront is first evaluated, resulting in an aberration-free transmitter and a slightly worse receiver, but still acceptable for altimetry applications. Finally, the prototype is aligned thoroughly and tested for timing measurements with single-pixel detectors, successfully providing the range to the target.
In the next instrument development phase, throughout the pre-phase A studies in collaboration with ESA (European Space Agency) and relevant companies, the prototype will be enhanced to verify the performance in the other criteria and test its functionality in a relevant environment with a flight campaign. ...
Since their first use during the Apollo 15, 16, and 17 missions, laser altimeters have become indispensable for planetary exploration, enabling topographic mapping of rocky bodies throughout the solar system. The latest European contributions in this field are represented by the BepiColombo Laser Altimeter (BELA) and the Ganymede Laser Altimeter (GALA), developed by the DLR Institute of Planetary Research and currently en route to Mercury and the Jovian moons, respectively. However, to date, such instruments have only been deployed on large satellites, failing to meet miniaturised systems' SWaP (Size, Weight, and Power) requirements.
This thesis investigates the adaptation of laser altimeter technology for smaller platforms, focusing on the NLA (New Laser Altimeter) developed for the SER3NE (Selene's Explorer for Roughness, Regolith, Resources, Neutrons, and Elements) mission proposal. The instrument aims to improve the precision of Lunar topographic data to support the characterisation of future landing sites for crewed missions from a 12 U microsatellite. To meet the stringent SWaP constraints, the design will feature a transceiver and a single-photon detection system — an approach never previously applied to topographic altimeters.
This thesis aims to develop an optical design that fits the instrument within a 3 U volume. Given the innovative nature of the design, a trade-off analysis was conducted to evaluate several configurations based on their compactness, cross-coupling between the laser source and detector, footprint size at the target, co-alignment between the transmitter and receiver, and transmission losses. The selected design stood out in providing a footprint size in the range allowed by the requirements, reducing the probability of damage to the detector due to internal reflections from the laser, and guaranteeing a more stable co-alignment between the transmitter and receiver paths. It includes a transmitter with two 45° folding mirrors, a borehole mirror that allows the laser to pass while deflecting the returning signal, and a shared telescope.
A test campaign is then conducted on a dedicated optomechanical design to assess 1) its compliance with some trade-off criteria and 2) its functionality. The expansion performance is demonstrated as predictable and reliable, guaranteeing the desired divergence and footprint at the target. On the other hand, the transmittance is increased above the constraints by varying the angle of incidence of the light on the band-pass filter. For the functional tests, the quality of the wavefront is first evaluated, resulting in an aberration-free transmitter and a slightly worse receiver, but still acceptable for altimetry applications. Finally, the prototype is aligned thoroughly and tested for timing measurements with single-pixel detectors, successfully providing the range to the target.
In the next instrument development phase, throughout the pre-phase A studies in collaboration with ESA (European Space Agency) and relevant companies, the prototype will be enhanced to verify the performance in the other criteria and test its functionality in a relevant environment with a flight campaign.
This thesis investigates the adaptation of laser altimeter technology for smaller platforms, focusing on the NLA (New Laser Altimeter) developed for the SER3NE (Selene's Explorer for Roughness, Regolith, Resources, Neutrons, and Elements) mission proposal. The instrument aims to improve the precision of Lunar topographic data to support the characterisation of future landing sites for crewed missions from a 12 U microsatellite. To meet the stringent SWaP constraints, the design will feature a transceiver and a single-photon detection system — an approach never previously applied to topographic altimeters.
This thesis aims to develop an optical design that fits the instrument within a 3 U volume. Given the innovative nature of the design, a trade-off analysis was conducted to evaluate several configurations based on their compactness, cross-coupling between the laser source and detector, footprint size at the target, co-alignment between the transmitter and receiver, and transmission losses. The selected design stood out in providing a footprint size in the range allowed by the requirements, reducing the probability of damage to the detector due to internal reflections from the laser, and guaranteeing a more stable co-alignment between the transmitter and receiver paths. It includes a transmitter with two 45° folding mirrors, a borehole mirror that allows the laser to pass while deflecting the returning signal, and a shared telescope.
A test campaign is then conducted on a dedicated optomechanical design to assess 1) its compliance with some trade-off criteria and 2) its functionality. The expansion performance is demonstrated as predictable and reliable, guaranteeing the desired divergence and footprint at the target. On the other hand, the transmittance is increased above the constraints by varying the angle of incidence of the light on the band-pass filter. For the functional tests, the quality of the wavefront is first evaluated, resulting in an aberration-free transmitter and a slightly worse receiver, but still acceptable for altimetry applications. Finally, the prototype is aligned thoroughly and tested for timing measurements with single-pixel detectors, successfully providing the range to the target.
In the next instrument development phase, throughout the pre-phase A studies in collaboration with ESA (European Space Agency) and relevant companies, the prototype will be enhanced to verify the performance in the other criteria and test its functionality in a relevant environment with a flight campaign.
FSO satellite communication enables data transfer at high bandwidths, low latency, and high security. Due to these benefits, FSO communication services with satellite constellations can hugely improve global connectivity and bandwidth, while maintaining sufficient security. Modeling a global FSO satellite communication service is beneficial for gaining insight into, and performing preliminary analysis on such missions. However, these missions are complex problems with several physical processes occurring at different time scales. Macroscopic processes in the order of minutes to hours consist of relative platform dynamics (eg. aircraft and satellite motion) and atmospheric attenuation. Microscopic processes consist of atmospheric turbulence- and platform disturbances in the order of milliseconds and transporting photons/bits in the order of nanoseconds. To our knowledge, there are currently no end-to-end models that accurately and efficiently simulate a combination of all these processes. To overcome this, a multi-scale method is proposed that simulates and combines the physics of the microscopic and macroscopic processes of a global FSO satellite communication mission. A bi-directional air-to-space link is chosen as a use case. The proposed model simulates a 1.5 hours communication mission in 6 minutes with 8 Gb random access memory (RAM). Platform dynamics and jitter are the most dominant effects. Including microscopic processes results in a performance difference in signal power of 10 dB to 80 dB depending on the strength of the atmospheric channel. Using the multi-scale method, we can efficiently and realistically simulate an FSO communication service end-toend between an aircraft and a satellite constellation.
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FSO satellite communication enables data transfer at high bandwidths, low latency, and high security. Due to these benefits, FSO communication services with satellite constellations can hugely improve global connectivity and bandwidth, while maintaining sufficient security. Modeling a global FSO satellite communication service is beneficial for gaining insight into, and performing preliminary analysis on such missions. However, these missions are complex problems with several physical processes occurring at different time scales. Macroscopic processes in the order of minutes to hours consist of relative platform dynamics (eg. aircraft and satellite motion) and atmospheric attenuation. Microscopic processes consist of atmospheric turbulence- and platform disturbances in the order of milliseconds and transporting photons/bits in the order of nanoseconds. To our knowledge, there are currently no end-to-end models that accurately and efficiently simulate a combination of all these processes. To overcome this, a multi-scale method is proposed that simulates and combines the physics of the microscopic and macroscopic processes of a global FSO satellite communication mission. A bi-directional air-to-space link is chosen as a use case. The proposed model simulates a 1.5 hours communication mission in 6 minutes with 8 Gb random access memory (RAM). Platform dynamics and jitter are the most dominant effects. Including microscopic processes results in a performance difference in signal power of 10 dB to 80 dB depending on the strength of the atmospheric channel. Using the multi-scale method, we can efficiently and realistically simulate an FSO communication service end-toend between an aircraft and a satellite constellation.
SRP-22 ALAR FOX
Fall DSE 2022: Regional Passenger Transport
Bachelor thesis
(2023)
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M. Cabañas Maldonado, M. Chou, M. Dinesh, B.B.W.M. Domhof, D.D. Doneva, T.P. Hokke, A. Lanza Rausell, A.P. Masle, G.C.J.O. Sa, I.E.M. van Teeffelen, R. Vos, N.D. Eskue, R. Saathof
This report entails the design of a regional passenger aircraft, serving 48 passengers and entering the market by 2035. It is known as the SRP-22 ALAR FOX, however, in general, SRP-22 is used. The propulsion system is designed with hydrogen as its fuel. The hydrogen is converted to electricity with a low-temperature proton-exchange membrane fuel cell, which in turn is used by the electric motors, to power the propellers. There are four electric motors with one six-bladed propeller each. Two propellers are located under the wing near the fuselage and deliver 80% of the total power. The remaining two propellers are positioned on the wing tips, delivering the remaining 20%. The benefit of these wingtip propellers is an expected drag reduction of around 10%, due to the attenuation of wingtip vortices.
The hydrogen is stored in a composite tank, located behind the aft pressure bulkhead. The fuel cell is placed under the cabin floor, just in front of the pressure bulkhead, such that less tubing is required to transport the hydrogen. The boil-off of the hydrogen is used to transform the hydrogen from its liquid state to its gaseous state, through the usage of glass rods. After that, the hydrogen is heated up until about 80◦C, which is the operating temperature of the fuel cell. The control system is controlled through a mechanical-powered hydraulic system. The elevator design includes horns to relieve the hinge moment.
One of the main goals was to reduce the environmental impact of the aircraft. The average temperature response of the SRP-22 is almost 83 times lower than that of the ATR 42 by 2064, which supports this goal. Noise has also been taken into account, which mainly stems from the propellers and airframe. It is found that the noise levels are well below the limits set by ICAO. The unit list price of the SRP-22 will be $19 million when using more optimistic fuel cell prices, while a least optimistic estimate results in a unit list price of $37 million. Moreover, the direct operational cost is around 10% lower than those of the ATR 72. Because of the usage of electric motors, the maintenance cost is expected to be lower than for a turboprop aircraft. ...
The hydrogen is stored in a composite tank, located behind the aft pressure bulkhead. The fuel cell is placed under the cabin floor, just in front of the pressure bulkhead, such that less tubing is required to transport the hydrogen. The boil-off of the hydrogen is used to transform the hydrogen from its liquid state to its gaseous state, through the usage of glass rods. After that, the hydrogen is heated up until about 80◦C, which is the operating temperature of the fuel cell. The control system is controlled through a mechanical-powered hydraulic system. The elevator design includes horns to relieve the hinge moment.
One of the main goals was to reduce the environmental impact of the aircraft. The average temperature response of the SRP-22 is almost 83 times lower than that of the ATR 42 by 2064, which supports this goal. Noise has also been taken into account, which mainly stems from the propellers and airframe. It is found that the noise levels are well below the limits set by ICAO. The unit list price of the SRP-22 will be $19 million when using more optimistic fuel cell prices, while a least optimistic estimate results in a unit list price of $37 million. Moreover, the direct operational cost is around 10% lower than those of the ATR 72. Because of the usage of electric motors, the maintenance cost is expected to be lower than for a turboprop aircraft. ...
This report entails the design of a regional passenger aircraft, serving 48 passengers and entering the market by 2035. It is known as the SRP-22 ALAR FOX, however, in general, SRP-22 is used. The propulsion system is designed with hydrogen as its fuel. The hydrogen is converted to electricity with a low-temperature proton-exchange membrane fuel cell, which in turn is used by the electric motors, to power the propellers. There are four electric motors with one six-bladed propeller each. Two propellers are located under the wing near the fuselage and deliver 80% of the total power. The remaining two propellers are positioned on the wing tips, delivering the remaining 20%. The benefit of these wingtip propellers is an expected drag reduction of around 10%, due to the attenuation of wingtip vortices.
The hydrogen is stored in a composite tank, located behind the aft pressure bulkhead. The fuel cell is placed under the cabin floor, just in front of the pressure bulkhead, such that less tubing is required to transport the hydrogen. The boil-off of the hydrogen is used to transform the hydrogen from its liquid state to its gaseous state, through the usage of glass rods. After that, the hydrogen is heated up until about 80◦C, which is the operating temperature of the fuel cell. The control system is controlled through a mechanical-powered hydraulic system. The elevator design includes horns to relieve the hinge moment.
One of the main goals was to reduce the environmental impact of the aircraft. The average temperature response of the SRP-22 is almost 83 times lower than that of the ATR 42 by 2064, which supports this goal. Noise has also been taken into account, which mainly stems from the propellers and airframe. It is found that the noise levels are well below the limits set by ICAO. The unit list price of the SRP-22 will be $19 million when using more optimistic fuel cell prices, while a least optimistic estimate results in a unit list price of $37 million. Moreover, the direct operational cost is around 10% lower than those of the ATR 72. Because of the usage of electric motors, the maintenance cost is expected to be lower than for a turboprop aircraft.
The hydrogen is stored in a composite tank, located behind the aft pressure bulkhead. The fuel cell is placed under the cabin floor, just in front of the pressure bulkhead, such that less tubing is required to transport the hydrogen. The boil-off of the hydrogen is used to transform the hydrogen from its liquid state to its gaseous state, through the usage of glass rods. After that, the hydrogen is heated up until about 80◦C, which is the operating temperature of the fuel cell. The control system is controlled through a mechanical-powered hydraulic system. The elevator design includes horns to relieve the hinge moment.
One of the main goals was to reduce the environmental impact of the aircraft. The average temperature response of the SRP-22 is almost 83 times lower than that of the ATR 42 by 2064, which supports this goal. Noise has also been taken into account, which mainly stems from the propellers and airframe. It is found that the noise levels are well below the limits set by ICAO. The unit list price of the SRP-22 will be $19 million when using more optimistic fuel cell prices, while a least optimistic estimate results in a unit list price of $37 million. Moreover, the direct operational cost is around 10% lower than those of the ATR 72. Because of the usage of electric motors, the maintenance cost is expected to be lower than for a turboprop aircraft.
Laser satellite communications for ground-to-ground and ground-to space links is influenced by atmospheric turbulence. Typically, theoretical models are used to predict link performance and the influence of the atmosphere on variables such as beam wander, spot size and scintillation at the receiver. These variables are used as input for system design. However, the models, which predict the individual variables have not yet been empirically verified for their individual contributions. Therefore, this paper focuses on retrieving the individual variables estimated by theoretical models from measurements representing these variables. These measurements have been retrieved in a 10 km uplink path, ground-to-ground field test. In this test, the receiver plane is imaged. The spot location and size and the longitudinal, radial and on-axis scintillation indices are estimated from the measurements. Also, turbulence strength is measured along the path and are used as inputs for the theoretical models. For weak turbulence conditions the theory and test results fall within the same order of magnitude. For all effects, except on-axis scintillation, the values predicted by theory lie at a slightly higher value than retrieved with the field test for the weak turbulence regime. For strong turbulence conditions the difference in results between theory and data grows, up to order one. To the authors’ knowledge, this is the first time the turbulence variables have been experimentally investigated in so much detail. It is clear from the differences, that both the experimental setup and theory for horizontal ground-to-ground links need attention to close the gap between them, especially for turbulence conditions outside the Rytov approximation range.
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Laser satellite communications for ground-to-ground and ground-to space links is influenced by atmospheric turbulence. Typically, theoretical models are used to predict link performance and the influence of the atmosphere on variables such as beam wander, spot size and scintillation at the receiver. These variables are used as input for system design. However, the models, which predict the individual variables have not yet been empirically verified for their individual contributions. Therefore, this paper focuses on retrieving the individual variables estimated by theoretical models from measurements representing these variables. These measurements have been retrieved in a 10 km uplink path, ground-to-ground field test. In this test, the receiver plane is imaged. The spot location and size and the longitudinal, radial and on-axis scintillation indices are estimated from the measurements. Also, turbulence strength is measured along the path and are used as inputs for the theoretical models. For weak turbulence conditions the theory and test results fall within the same order of magnitude. For all effects, except on-axis scintillation, the values predicted by theory lie at a slightly higher value than retrieved with the field test for the weak turbulence regime. For strong turbulence conditions the difference in results between theory and data grows, up to order one. To the authors’ knowledge, this is the first time the turbulence variables have been experimentally investigated in so much detail. It is clear from the differences, that both the experimental setup and theory for horizontal ground-to-ground links need attention to close the gap between them, especially for turbulence conditions outside the Rytov approximation range.