Understanding the intricacies of Venus is key in the field of planetary science and provides invaluable insights into the evolution of Earth. A promising way of studying the Venusian environment involves the use of aerobots active in the benign region of the atmosphere. However, balloon missions to Venus, whether already conducted or just proposed, all suffer from very short mission life-time due to issues with sustained lifting.

Here, we present the VISTA mission concept. The mission concept proposes a solution to long-endurance aerobot flight on Venus through the use of in situ nitrogen extraction. The nitrogen content of the Venusian atmosphere in the convective cloud layer (50-60 km altitude) is about 3.5%. Obtaining nitrogen from the atmosphere can potentially provide a long-term supply of lifting gas, solving the unavoidable problem of lifting gas leakage. Greatly extended potential mission duration allows for much more extensive studies of the large scale wind patterns and detailed investigations of the atmosphere through time. It also enables the study of Venus’ interior, including detection of rare seismic events. The present work proposes a detailed mission concept for a long-term balloon-based aerobot that aims to uncover the mysteries of Venus. ... Read more

GNSS jammers can disrupt critical positioning, navigation, and timing services. Low Earth orbit satellites offer a way to locate these emitters over large areas. This thesis studies passive geolocation of stationary terrestrial GNSS jammers with a three-satellite LEO system.

Two geolocation approaches are compared. The first estimates emitter positions directly from received I/Q data. The second first extracts receiver-differenced observables and then estimates position from FDOA measurements. These approaches are referred to as direct and indirect geolocation. A parametric simulation framework is developed to model the satellite formation, jammer signals, receiver data, and main error sources. A CRLB analysis is used to study the design space.

The results show that both approaches can achieve sub-kilometer per-emitter accuracy. In Scenario 1, the direct method reaches a mean error of 502m, while the indirect method reaches 143m. In Scenario 2, the corresponding values are 517m and 292m. The indirect method also provides precision estimates through 95\% confidence ellipses. Its main advantage is computational cost. It is about 900 times faster per snapshot in the reported implementation.

The results also show that a tight formation is preferred. It maximizes the shared field of view while keeping enough geometric diversity. The FDOA loop-closure constraint is found to be essential. It rejects false candidates and makes indirect geolocation practical in a multi-emitter setting.

This thesis concludes that FDOA-based indirect geolocation with a tight three-satellite LEO formation is the most suitable option for low-latency wide-area GNSS interference geolocation within the considered scope. Future work should validate the method with more scenarios or real satellite data. ... Read more

The GRACE/GRACE-FO mission has provided Earth's monthly gravity field data for more than 20 years. It has been a major success and has enabled significant contributions across multiple domains (e.g., water management, cryosphere monitoring, solid Earth sciences). Nonetheless, short-periodic effects are undersampled, and the data is noisy at high spatial frequencies, leading to north-south stripes in gravity field functionals. Future gravity research missions aim at improving both spatial and temporal resolution to fulfil increasingly demanding science and societal needs. In this work, an analytical spectral methodology is employed to study gravity field recovery capabilities of different configurations: GRACE-like, Bender configuration, and multi-satellite pairs configurations. The analytical model underestimates GRACE operational performance by almost one order of magnitude. Application of NGGM performance to a Bender configuration shows the observability of the atmospheric and ocean non-tidal signal with a resolution of 200 km. Moreover, the theoretical feasibility of daily and 3-hour solutions with 3 and 48 satellite pairs, respectively, is demonstrated, with a resolution of roughly 1000 km, assuming CubeSat performance. In this way, future missions might not only improve spatio-temporal resolution but also mitigate other error sources.
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In this report, the preliminary design and sizing of a long-duration stationary Venus lander named KYTHERA is performed. In contrast with previous Venus landers, KYTHERA is designed to survive on the hellish Venusian surface for at least 200 Earth days to study long-term atmospheric and seismic phenomena. In addition to the chemical analysis of the atmosphere and seismic measurements, the lander is capable to do 20 individual chemical analyses of surface rock material, using Laser-Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy. To meet the duration goal, the lander is actively cooled, using a Stirling-generator-cooler chain to remove heat from the inside, powered by the radioactive decay of plutonium. The corrosion and heat resistant structure is sized to survive 120 Earth G-s of acceleration during entry and a landing impact speed of 8.5 m/s, as well as 93 bars of pressure difference at 460 °C. To maximize insulation efficiency, the internal structure of the lander (the coldbox) is separated from the outer shell (the hotbox) by 3.5 cm of vacuum. Although the mission is expected to fit within the required mass budget, the cost is likely to be exceeded, as the power system is more expensive than initially anticipated. The lander weighs 350 kg and is expected to cost around 300 million euros. ... Read more

Due to recent improvements in the quality of DORIS and GNSS observations, the achievable quality in real-time orbit determination has improved drastically, achieving radial position accuracies down to 3 cm. The limited amount of computational power available in real-time scenarios results in a need for more computationally efficient yet still sufficiently accurate dynamical models.
An important aspect of this model is the set of dynamics used to solve for the state transition and sensitivity matrices, which describe the change in orbital state that can be achieved by an earlier change in the orbital state or dynamic parameters. In this work, an approximation of these state transition and sensitivity matrices was investigated, based on the Hill-Clohessy-Wiltshire equations of relative orbital motion. We show that these approximations result in significant computational savings and that they are compatible with centimetre-level orbit determination. ... Read more

Understanding the role of ocean swell, monitoring and modelling it is critical for a diverse range of oceanographic research, coastal management initiatives and for better weather forecasting and climate modelling.
Currently, swell measurements are obtained through in-situ measurements, wave models, and satellite measurements. So far, swell wave parameters have been retrieved from orbit using optical instruments, imaging radars and wave spectrometers. The potential to retrieve swell wave spectra from radar altimeters was recently demonstrated using fully focused synthetic aperture radar (FFSAR) signal processing.
Sentinel-6 (S6) would be a good candidate for investigating the potential of swell parameter retrieval, however, no study has been performed regarding the impact that the on- board data compression/ waveform truncation mode of S6 could have on the retrieval of swell parameters. Swell wave period estimates were thus derived from the raw and compressed S6 FFSAR waveforms collected over a study area in the Channel Islands of California during a 22 month- period. A performance analysis was carried out comparing the period estimate pairs from a given timestamp with the records obtained by a buoy in the study area at the same time.
The study demonstrated the presence of differences in the performance of swell period retrieval for the different operating modes of S6. It was found that swell period estimates can be derived also from the compressed waveform signal, obtaining however a lower accuracy compared to raw waveforms. ... Read more

This summary is about the highlights of the final design of the LAMP (Low Altitude Modular Platform). This report follows the project plan, baseline report and midterm report. This report presents the market analysis for the platform followed by the detailed design of the platform. The design of each subsystem is treated on its own after which the integration, manufacturing and operations of all subsystems are discussed. The low-altitude modular platform is a versatile satellite platform with a wide range of capabilities. It bridges the gap between small CubeSats and high-end Earth observational satellites, while also flying at 300 Km, enabling higher resolutions in a small form factor. While the market share of CubeSats has grown a lot in recent years, their capabilities are still limited. Due to practical constraints of miniaturisation, the spacecraft bus platform typically occupies approximately 50% to 80% of the total satellite internal volume. This problem is however remedied with the use of larger satellites, which is the market gap LAMP tries to occupy. It has both the advantages of standardisation, ease of production, and low cost of CubeSats, while also possessing a large payload fraction and the bus capabilities to accommodate a high-end earth observation payload. LAMP is also innovative in its communication capabilities: It is planned to be the first satellite platform to use the SpaceX Starlink constellation. This gives LAMP unparalleled communication capabilities for an earth observational satellite in its class. LAMP is capable of sending all the information of its design payload (the DST) in livelink. In certain orbits, it is even capable of streaming 1080p 60fps video live to Earth. This opens it for a great number of new applications related to civil, law enforcement, and military surveillance... ... Read more

To answer the question of habitability of other planets, it is crucial to find liquid water. As a planet’s surface might be difficult to characterise through observations, the observation of cloud composition and coverage could possibly reveal the presence of large bodies of surface water. Climate code SPEEDY is used to investigate relations between cloud patterns on rocky exoplanets with oceans for various planet parameters, such as obliquity and incident stellar flux, and the observable signals of such exoplanets are computed. SPEEDY was chosen for the modelling of rocky exoplanets, because of its speed, since our aim is to run simulations for various planet parameters, and its flexibility, since it allows the adaptation of planet properties such as the presence and distribution of continents. The planet’s rotational period is found to have the most obvious influence on the cloud pattern: with increasing rotational speed, bands of clouds form, parallel to the equator, with the number of bands increasing with the rotational speed. The total flux and polarisation of starlight that is reflected by the planets with cloud bands as functions of the wavelength and the planetary phase angle are computed. Also the influence of the integration time of the observations on the reflected light signals is studied. Our main recommendation for further research is to broaden the applicability of SPEEDY for exoplanet research by first gaining more insight into the parametrisations and then by adapting them where necessary to allow wider parameter settings. ... Read more

My research investigates the (initial) orbit determination (IOD) problem for short-arc angle-only optical observations of satellites. The method is an adaptation of the Constrained Admissible Region Multiple Hypothesis Filter (CAR-MHF) method, as developed by DeMars et al. This adapted method is tested on data obtained from telescopes, where publications by DeMars only tested the method on simulated data. The adapted method of the CAR-MHF was only able to perform IOD for single observation arcs due to the use of the EKF. The CAR-MHF is compared to Gauss’s method, for 582 satellites which had an observation arc with a minimum of 3 data points, the minimum number of observations required. The accuracy performance of both methods are comparable. The CAR-MHF was able to find an IOD solution for 242 satellite, almost 20% more than Gauss’s method. This research is a stepping stone to improve the CAR-MHF method for real-world data applications. ... Read more

The future space environment is predicted to grow in number of both operational and inactive man-made objects and the era of constellations is expected to arrive during the following years, with many telecom companies launching constellations of up to 12000 satellites. This situation will inevitably lead to over-population of the most demanded orbits making its exploitation a challenge to the scientific community as well as spacecraft operators.
Regular products within the field of Space Surveillance and Tracking (SST) and Space Traffic Management (STM), such as high-risk collisions, upcoming re-entries or fragmentations, rely both on the estimated state and associated uncertainty of detectable Resident Space Objects (RSOs). Orbit Determination (OD) algorithms provide the required estimations, assuming that the uncertainty in the state of the object is properly characterized by its state vector covariance and assuming Gaussian processes. However, a common problem of OD processes is the misrepresentation of the RSOs uncertainty through the estimated and predicted covariance. Ultimately, this causes a great impact in the quality and accuracy of SST products as the covariance is overly optimistic (too small) and the true uncertainty of the object is not properly captured. The aim of this work is to devise a novel methodology to improve the covariance realism of OD and orbit propagation processes through the classical theory of consider parameters of batch least-squares estimators. The outcome of this project is a software application integrated as part of the GMV’s SST software suite that can deliver efficient and effective covariance realism improvement for a more accurate provision of SST products. ... Read more

Accurately tracking the trajectory of launching vehicles during the boost phase is crucial for a variety of reasons. First, an accurate burnout point location and  velocity of the launch vehicle will facilitate the estimation of its trajectory during the following phases of ballistic flight and the impact location. This has important implications for safety purposes. The first stage of many launcher systems such as the Russian Soyuz or the Chinese Long March rockets commonly impact on land, sometimes on populated areas. Furthermore, the proliferation of suborbital rocket launches presents a hazard if regulations are not properly followed. Therefore, it becomes critical to estimate the impact point of any vehicle that reenters the lower layers of the atmosphere beforehand, during the boost phase, in order to prevent personal and material damage. Second, a critical aspect in any space mission is to insert the payload into the required orbit. An accurate tracking of the launcher system during the boost phase allows carrying out early orbit determination in order to successfully complete the payload insertion. In this Master Thesis, an analysis and performance comparison of different tracking algorithms for launching vehicles during boost (e.g. launcher systems or suborbital rockets) has been carried out. This type of tracking problem has several difficulties that must be overcome. First, the unknown thrust profile – thrust magnitude and orientation – of a launching vehicle makes difficult to develop motion models that can accurately describe its behavior. Second, the observations of the plume of the launching vehicle obtained from two line-of-sight passive sensors located in geostationary satellites are used. The way these observations are obtained does not allow to accurately measuring the initial state and trajectory of the vehicle, complicating the initialization and the trajectory estimation processes of the tracking filters. Finally, the nonlinearities present in the system and measurements models of the tracking filters compel us to devise linearization schemes or the implementation of alternative filtering methods.The work presented in this document has been developed at the Military and  Security department of Airbus Defense and Space, as a continuation of an ongoing project. To solve the aforementioned difficulties of the tracking problem, a tracking system – EKF-Tool – was developed at ADS previous to the start of this Thesis. Nevertheless, this tool shows several limitations that hinder its performance, even preventing from successful tracking. In this Thesis, the limitations and potential areas of improvement of the EKF-Tool have been analyzed. Based on the results of this analysis, an alternative tracking algorithm – PKF-Tool – is introduced with the aim of overcoming the limitations of the EKF-Tool. The tracking performance of both tools has been tested using several indicators: stability, consistency, credibility, accuracy, precision, and versatility.  ... Read more

CryoSat-2 is a European Space Agency (ESA) altimeter mission with an objective to study the connection between cryosphere melting and global sea level rise. The satellite carries a Doppler navigation system (DORIS) and a Satellite Laser Ranging system (SLR) to aid the precise computation of orbits down to centimetre level.
CNES/IDS releases DORIS tracking data in two formats for CryoSat-2. One is the raw format called RINEX and other is the pre-processed Doppler format called version 2.2. V2.2 data contains all information necessary for straightforward usage in orbit determination - measurements time-tagged in TAI, range-rate measurements, ionospheric correction, tropospheric correction, antenna corrections and flags that indicate unusable measurements. RINEX does not contain any corrections and has the phase and pseudorange measurements at short latency allowing users to have flexibility in processing. Additionally, data required for formulating the corrections are present in RINEX. For missions in and after 2016, CNES/IDS supplies tracking data only in RINEX and not in V2.2. Analysis centres using DORIS data now have to independently develop processing strategies to process RINEX data. This problem is the main objective of this research. In this thesis, a pre-processor called RX2RR (RINEX to Range-Rate) has been built in Fortran in an attempt to process the raw data and compute all the necessary corrections. RX2RR converts RINEX format to a format exactly similar to V2.2 such that RINEX can now be used in any orbit determination tool that has been previously using V2.2. In this processor, clock synchronisation of on-board clock to International Atomic Time is performed. A new approach of utilizing Meteorological data in RINEX for troposphere delay corrections is implemented. Use of real time data from numerical weather models is also presented for tropospheric correction. Ionospheric delay and antenna phase centre corrections are performed using iono-free phase centre. An editing strategy to remove outliers in Doppler data is implemented and tested. To demonstrate the performance of the tool, we perform orbit determination using NASA Goddard Space Flight Center’s orbit computation software GEODYN-II. We use RX2RR processed RINEX data and CNES processed V2.2 data of CryoSat-2 for year 2016. Tracking residuals from both POD runs are compared and average difference in R.M.S residual is found to be approximately 0.011 mm/s over a year. This validates that the corrections are formulated and implemented correctly. The result proves our capability to process the RINEX measurements independently and the tool developed has extended the capability of GEODYN-II to process RINEX observations from DORIS system. ... Read more

Piazzi is a mission to the 1989 UQ asteroid, with the goal of collecting a sample and returning it to Earth. This will be accomplished by sending a spacecraft to the asteroid, which will consist of three separate spacecraft. Firstly the orbiter, which houses the instruments needed to observe and map the asteroid, and the primary propulsion and communications systems. Then two spacecraft will detach from the orbiter, and each collect a sample in a distinct manner. One, ACSAL, will land on the asteroid, and collect a core sample using a drill. The other, SASH, will hover above the surface, and collect a regolith sample. Both ACSAL and SASH will return to Earth individually, shoot off a reentry capsule with the sample and burn up in the atmosphere themselves. ... Read more

The military use of space brings interesting challenges for both technology and operational aspects. The Netherlands armed forces are a small player within the military world. However, in 2013 the beginning of a space program was started by the Royal Netherlands Air Force (RNLAF). One of the key mission statements
stated: “show the military relevance of Nano Satellites". A feasibility study was conducted and the realisation of the first satellite, the BRIK-II,was started. One of the payloads of this satellite is a store and forward system. In this thesis work a systems engineering approach towards, requirements definition, design, verification and testing is provided. ... Read more

Cryosat-2 altimetry helps to assess the state of the Cryosphere by measuring elevation and elevation change. The SARIn mode of the Cryosat-2 SIRAL instrument is specifically designed for rough topography that we encounter near ice sheet margins. Various SARIn data products (Full Bit Rate (FBR), Level 1b and Level 2) are provided by ESA, where the level denotes the amount of processing applied relative to the raw instrument data. Often research activities are based on L1b data; in this thesis, a new Cryosat-2 SARIn FBR-to-L1b processor is developed to evaluate whether elevation measurements improve when we reconstruct a L1b product from the FBR data. The L1b-to-L2 processing is performed by means of Swath Processing, by which an increase in amount of measurement points is achieved with respect to the amount in conventional L2 products. The analysis is limited to the Petermann glacier, located in the North-West of Greenland, which is known for its large calving events. The results are verified by comparing them to the ESA products. It is shown that the resulting elevations following from the FBR-to-L1b processor agree; we detect significant variability in topography as present in the Petermann Glacier region that can induce data gaps in the raw FBR data; with consequences for the L1b- and L2 products. Overall, it is shown that small improvements in terms of accuracy can be achieved with respect to the ESA L1b data; this conclusion follows from the consideration of independent IceBridge laser altimetry data in our study. ... Read more

The Equivalence Principle is today challenged by some theories attempting to unify General Relativity and Quantum Mechanics. The MICROSCOPE mission thus intents to confirm or overturn this principle by testing the universality of free fall in space with an unrivaled precision objective of 10^-15. The principle of the test relies on the precise measurement of a gravitational signal by a differential electrostatic accelerometer (referred to as SAGE instrument) on board a drag-free microsatellite. The precision of the measurements exploited for the test is limited by several perturbations due to the high sensitivity of the instrument. The instrumental model implemented to process the collected data used overestimated models for some systematic errors such as the thermal sensitivity and coupling defects. The additional scientific measurements available by the end of the mission, will enable to perform a more in-depth exploration of these errors and thus to improve the current instrumental model. This is the purpose of this research work. ... Read more

Electric low-thrust propulsion has nowadays found wide application in space dynamics as it entails considerable savings in spacecraft propellant mass, thanks to the very high specific impulse that this kind of engine is able to generate. However, continuous thrust opens new extensive sets of feasible trajectories, and optimization algorithms are needed to mine the admissible search space and find optimal transfers. Practical methods to solve complex optimal control problems as low-thrust trajectory optimization typically involve high computational times, the major bottleneck of these techniques. The objective of this work is the development of a novel multiple-shooting optimization tool, employing a variational approach for quick derivative computation, and the assessment of its performance against a variety of test cases. Indeed, after a first analysis of practical optimization methods, the derivative estimation by finite-difference approximations has been found as the major contributor to the computational burden, and the propagation of the variational dynamics has been selected as an accurate approach to speed-up their computation. The theory of variational dynamics for multiple-shooting application has been analyzed in detail, and further developed for what concerns the second-order equations. After practical considerations on the method implementation (scaling procedures, sparsity patterns, et cetera) and its interface with WORHP, the selected non-linear programming solver, the tool has been applied to a broad range of test cases, spanning from elementary problems to practical applications. For what concerns the latter cases, two complex problems were analyzed and optimized: a CubeSat rendezvous departing from Earth-Moon L2 and arriving at asteroid 2000SG334, resulting in a propellant mass convenient trajectory suitable for asteroid reconnaissance well before a proposed NASA manned mission in 2069; The Kessler Run, i.e. the 9th Global Trajectory Optimization Competition (GTOC9), in which the developed tool, employed as last step of the optimization cascade of Strathclyde++ team, managed to make the solution constraint-feasible, valid and further mass-optimal. ... Read more

This report presents the Final design of the Design Synthesis Exercise (DSE) to 'Capture a Small Asteroid and Change its Orbit' at the Faculty of Aerospace Engineering at Delft University of Technology. The bachelor programme 'Aerospace Engineering' comprises several projects enabling students to explore aeronautics and space from different kinds of perspectives. The Design Synthesis Exercise serves as the conclusion to this programme. During this final project students integrate their previously obtained knowledge and skill to examine a specific design problem in groups of ten students for the duration of eleven weeks. This final report is the last in a series of four and documents the detailed design of the concept that was chosen in the mid-term report. ... Read more