The increasing importance of Vision-Based Navigation (VBN) algorithms in space missions raises numerous challenges in ensuring their reliability and operational robustness. Sensor faults can lead to inaccurate outputs from navigation algorithms or even complete data processing faults, potentially compromising mission objectives. Artificial Intelligence (AI) offers a powerful solution for detecting such faults, overcoming many of the limitations associated with traditional fault detection methods. However, the primary obstacle to the adoption of AI in this context is the lack of sufficient and representative datasets containing faulty image data. This study addresses these challenges by focusing on an interplanetary exploration mission scenario. A comprehensive analysis of potential fault cases in camera sensors used within the VBN pipeline is presented. The causes and effects of these faults are systematically characterized, including their impact on image quality and navigation algorithm performance. To support this analysis, a simulation framework is introduced to recreate faulty conditions in synthetically generated images, enabling a systematic and controlled reproduction of faulty data. The resulting dataset of fault-injected images provides a valuable tool for training and testing AI-based fault detection algorithms. The final link to the dataset will be added after an embargo period. For peer-reviewers, this private link¹ is available.

This paper introduces a motion planning method for capture of tumbling objects using a free-floating space robot. The proposed approach incorporates an improved Rapidly Exploring Random Tree Star (RRT*) algorithm enabling obstacle avoidance and generating desired trajectories for the robot's end-effectors. Additionally, a multi-layer optimization process and a greedy policy are proposed to achieve singularity avoidance, joint velocity, and acceleration optimization by leveraging the robot arm's joint energy distribution, torque, and manipulability. By adopting this motion planning strategy, the space robotic system demonstrates improved performance in obstacle and singularity avoidance, without the need for inverse Jacobian matrix calculations. Furthermore, the multi-layer optimization process enhances trajectory smoothness and reduces end-effector vibration through energy and torque optimization. This research contributes to advancing space robotic systems by enhancing the entire energy and torque consumption on motion planning to make the end-effector move smooth and reduce the vibration.

The drag coefficient C_D of a satellite is an important input for predicting satellite orbits in low Earth orbit, but determining C_D is difficult due to limited knowledge of Gas-Surface Interactions (GSI), leading to orbit prediction errors and increased collision risk. We propose an experiment that leverages the concept of differential drag to gain more insight into GSI, as differential drag causes a varying frontal area and C_D while other conditions stay the same, allowing us to estimate GSI parameters using orbit determination. Both analytical and numerical methods to obtain C_D and their sensitivity to GSI parameters are discussed, and these methods are then used to determine the optimal maneuvers for the experiment. As a case study, simulations are shown of a planned experiment using the BRIK-II satellite of the Royal Netherlands Air Force. It is expected that this method can be used to obtain more knowledge on GSI modelling, as well as give satellite operators a method to estimate C_D of a satellite with less bias than conventional methods.

There is an increasing interest in science and exploration missions in the Earth-Moon system. These missions call for simple, efficient and accurate timing onboard of these spacecraft. A heterogeneous onboard timing system is proposed, presented and characterized, which comprises an Oven-Controlled Crystal Oscillator (OCXO) and one or several Chip Scale Atomic Clocks (CSACs), providing nano-second timing accuracy on time scales of seconds to hours. To extend the stability of this system to days, weeks and months, it is assisted by a Global Navigation Satellite Systems (GNSS) timing receiver, which is operated in snapshot mode and activated only for very short time durations of a few seconds on a daily or weekly basis, based on the mission needs. This innovative GNSS assistance replaces the ground-based synchronisation and offers an autonomous operations of the onboard timing system. In this way, a highly accurate yet very low Size, Weight and Power (SWaP) system can be realized, which can be used on very small satellites down to nano-satellites. The onboard architecture of this system is presented and characterised in terms of its achievable Allan deviations as well as its SWaP. It is found that the average power consumption can be as low as 2.2 W, based on a daily GNSS synchronisation schedule, significantly reducing the power requirements over current state-of-the-art solutions. An even less complex variant of this innovative system can be employed for any deep space or planetary mission, replacing the onboard GNSS timing receiver by a traditional time synchronisation mechanism using a terrestrial ground station, or, in the further future, using a pulsar.

In recent years, advancements in semiconductor technologies have significantly transformed Radio Frequency Power Amplifiers (RFPAs), enhancing their efficiency, size, and performance. Despite these advancements, the design of RFPAs remains intrinsically linked to the specific applications for which they are intended. What proves effective in one context, such as communication technologies, may not be equally suitable in others, such as scientific instruments. This discrepancy highlights the lack of a systematic approach to RFPA design that can be applied across different applications. This paper delves into the fundamental concepts of RFPA design, adopting a comprehensive perspective. It further introduces an alternative categorization of RFPAs, thereby providing a generalized design approach.

Uncertainty in atmospheric density models and drag coefficient modelling contributes to orbit prediction errors for satellites in Low Earth Orbit (LEO).
It is of interest to better characterise the Gas-Surface Interactions (GSI) to improve drag coefficient modelling, which is, however, hindered by a lack of dedicated in-orbit experiments. We propose a new experiment to estimate the energy accommodation coefficient of the Diffuse Reflection with Incomplete Accommodation (DRIA) GSI model. The experiment consists of two small satellites with Global Navigation Satellite Systems (GNSS) receivers and attitude determination systems to derive atmospheric density observations from the positioning data. The experiment has two key features. The first is the satellites' close along-track formation flying, such that they should observe the same atmospheric density with a slight delay due to their along-track separation. Second, the satellites have controllable panels to modify their drag coefficients' response to GSI substantially. Hence, the satellites' atmospheric density observations will agree only when the DRIA model's energy accommodation coefficient is selected correctly. We demonstrate by simulation that the energy accommodation coefficient can be estimated at least once daily with a precision of 5-10% for satellites with decimeter-accuracy GNSS positioning. Given that GNSS receivers and attitude determination systems are common for small satellites currently in LEO, we conclude that there are plenty of opportunities to utilise existing data for the proposed experiment. Valuable byproducts would be atmospheric density observations that are relatively free of systematic errors.

Traditional laser communication terminals are limited to point-to-point links, which constrains their scalability and flexibility for global networks that require simultaneous connections with multiple targets. While multiple single-beam terminals can expand capacity, this approach multiplies Size, Weight, Power, and Cost (SWaPC), limiting scalability. Multi-beam laser communication terminals offer a promising alternative, though the design of an effective beam steering system remains a key challenge. This paper explores the design process of such a system, providing an overview of multi-beam steering literature as well as an comparison and trade-off of existing space-borne multi-beam steering technologies. It also analyzes insights from related fields such as terrestrial laser communications, LiFi, single-beam laser communication, optical cross-connects, radio links, and multiple target tracking. Key system functions are identified and visualized in a function flow diagram, and various design options are evaluated, culminating in a design options tree which serves as a design recipe. Two application scenarios, involving high and low target densities, demonstrate that steering systems based on micro-mirror arrays and spatial light modulators present significant advantages over alternatives. This study offers a comprehensive framework for designing multi-beam steering systems for space-based laser communication terminals.

Traditional anomaly detection techniques onboard satellites are based on reliable, yet limited, thresholding mechanisms which are designed to monitor univariate signals and trigger recovery actions according to specific European Cooperation for Space Standardization (ECSS) standards. However, Artificial Intelligence-based Fault Detection, Isolation and Recovery (FDIR) solutions have recently raised with the prospect to overcome the limitations of these standard methods, expanding the range of detectable failures and improving response times. This paper presents a novel approach to detecting stuck values within the Accelerometer and Inertial Measurement Unit of a drone-like spacecraft for the exploration of Small Solar System Bodies (SSSB), leveraging a multi-channel Convolutional Neural Network (CNN) to perform multi-target classification and independently detect faults in the sensors. Significant attention has been dedicated to ensuring the compatibility of the algorithm within the onboard FDIR system, representing a step forward to the in-orbit validation of a technology that remains experimental until its robustness is thoroughly proven. An integration methodology is proposed to enable the network to effectively detect anomalies and trigger recovery actions at the system level. The detection performances and the capability of the algorithm in reaction triggering are evaluated employing a set of custom-defined detection and system metrics, showing the outstanding performances of the algorithm in performing its FDIR task.

Steering multiple laser beams using spatial light modulators (SLMs) creates unwanted diffraction and reflections that are not modulated by the SLM, which can make beam tracking difficult. A novel, to the best of our knowledge, and simple beam steering methodology is proposed, which aims at reducing the influence of this clutter while maintaining tracking performance. The beam(s) are deliberately defocused before steering with a superposition of a phase ramp and Fresnel lens (PRFL) phase screen on the SLM. As a result, the non-modulated reflections and diffracted light are decreased in relative intensity to the steered beam, in turn allowing simple and standard peak intensity and center of gravity (CG) algorithms for tracking. Hardware demonstration shows tracking performance using the PRFL remained on-par with more complex filtering approaches while adding no additional hardware. This method has potential to improve the communication performance of multi-beam laser communication terminals.

The need for higher data rates has transitioned the satellites towards laser communication, opening up new opportunities for inter-satellite distance measurements. The stringent requirements for space missions like gravimetry, formation flying, collision avoidance, and precise orbit determination require highly precise distance knowledge, which can be offered by lasers. The past and present missions depend on radio ranging and laser interferometers to achieve up to centimeter-order and picometer-order precision, respectively. However, these methods either require additional hardware or interfere with the communication data rates as the power available is shared between communication and ranging operations. Therefore, this research explores the potential of laser communication terminals in measuring the inter-satellite distance. Numerical simulations are performed to analyze the effect of the precision of inter-satellite distance measurements on atmospheric density estimation. The analysis shows that such range measurements can only improve atmospheric density estimates if the uncertainty in the drag coefficient can be reduced below the current range of 3-5%.

The accurate measurement of inter-satellite distances is fundamental to the successful operation of distributed spacecraft missions, facilitating diverse applications ranging from scientific exploration to navigation and communication. This study comprehensively overviews applications requiring inter-satellite tracking by analyzing 44 multi-spacecraft missions. These missions are divided into seven categories based on their use of inter-satellite distance measurements. Each category necessitates varying levels of accuracy, prompting the utilization of distinct tracking methods. The analysis reveals that missions near Earth typically rely on Global Navigation Satellite Systems measurements, achieving millimeter-level accuracy, while lunar missions opt for radio ranging for centimeter-level accuracy. Inter-satellite Laser Ranging Interferometry emerges as the preferred method for missions demanding exceptionally high accuracy (nanometer to picometer range), such as those dedicated to gravitational wave detection and gravimetry. Notably, the analysis identifies a burgeoning trend towards the adoption of Inter-satellite Laser Transponder Ranging, capable of achieving sub-millimeter accuracy. Furthermore, this work proposes a novel concept: integrating inter-satellite ranging with Laser Communication Terminal (LCTs), either to substitute for existing tracking methods or to enhance measurement accuracy within established frameworks. However, its full potential rests upon the successful adaptation of existing LCTs for ranging functionality without compromising data rates. Future research will play a critical role in quantifying achievable ranging performance by characterizing systematic errors within LCTs.

There is an increasing interest in science and exploration missions in the Earth-Moon system. These missions call for simple, efficient and accurate timing onboard of these spacecraft. A heterogeneous onboard timing system is proposed, presented and characterized, which comprises an Oven-Controlled Crystal Oscillator (OCXO) and one or several Chip Scale Atomic Clocks (CSACs), providing nano-second timing accuracy on time scales of seconds to hours. To extend the stability of this system to days, weeks and months, it is assisted by a Global Navigation Satellite Systems (GNSS) timing receiver, which is operated in snapshot mode and activated only for very short time durations of a few seconds on a daily or weekly basis, based on the mission needs. This innovative GNSS assistance replaces the ground-based synchronisation and offers an autonomous operations of the onboard timing system. In this way, a highly accurate yet very low Size, Weight and Power (SWaP) system can be realized, which can be used on very small satellites down to nano-satellites. The onboard architecture of this system is presented and characterised in terms of its achievable Allan deviations as well as its SWaP. It is found that the power consumption can be as low as 2.2 W, based on a daily GNSS synchronisation schedule, significantly reducing the power requirements over current state-of-the-art solutions. An even less complex variant of this innovative system can be employed for any deep space or planetary mission, replacing the onboard GNSS timing receiver by a traditional time synchronisation mechanism using a terrestrial ground station, or, in the further future, using a pulsar.

This paper proposes a novel concept of using highly efficient Snapshot Global Navigation Satellite Systems (GNSS) receivers to provide precise position fixes of single or multiple satellites in Low-Earth Orbit (LEO) to improve upper atmospheric modeling and thus contribute to superior space situational awareness (SSA). While tracking of LEO satellites and the use of onboard GNSS receivers for drag measurements and upper atmosphere modeling are well-established techniques, the expected advent of snapshot GNSS receivers for spaceborne scientific applications will allow massive improvements on the GNSS sensor's Size, Weight, Power and Cost (SWaP-C). With chip-size dimensions of 4x4 mm², a mass of less than 5 gr, an average power level below 0.1 mW, snapshot receiver technology is expected to provide position fixes in space with an accuracy of ∼19 m (3D r.m.s.), which will surpass the accuracy of Two-Line Elements (TLE) provided by the US Joint Space Operations Center (JSpOC) by at least two orders of magnitude. Equally important to their SWaP-C benefits, Snapshot GNSS receivers will allow mission and spacecraft designers to trade onboard-processing requirements versus payload downlink requirements, leading to either minimum onboard processing or a minimum amount of downlinked data. In this research, we establish the concept and architectural overview of using snapshot GNSS receivers for SSA, including the role of using them in a Distributed Space System (DSS), and detail their characterization and performance in terms of the required GNSS hardware and the impact of these payload on the power budget, the link budget and the OnBoard Data Handling (OBDH) budget of a satellite. It will be shown that these receivers lend themselves especially to their use on femto-, pico- and nano-satellites, although integrated snapshot modules may be flown as auxiliary payloads on micro- or mini-satellites as well. While this work focuses on the implications of the use of snapshot GNSS receivers on spacecraft design for the use of upper atmosphere modeling and SSA, their use may open up other science applications which avoid the need for expensive high-grade GNSS receivers.

Mitigation strategies to eliminate existing space debris, such as with Active Space Debris Removal (ASDR) missions, have become increasingly important. Among the considered ASDR approaches, one involves using a net as a capturing mechanism. A fundamental requirement for any ASDR mission is that the capture process itself should not give rise to new space debris. However, in simulations of net capturing, the potential for structural breaking is often overlooked. A discrete Multi-Spring-Damper net model was employed to simulate the impact of a 30 m × 30 m net travelling at 20 m/s onto an ESA Envisat mock-up. The Envisat was modelled as a two-rigid-body system comprised of the main body and a large solar array with a hinge connection. The analysis revealed that more than two significant substructures had a notable likelihood of breaking, prompting the recommendation of limiting the impacting velocity. The generation of secondary space debris indicates that net capturing is riskier than previously assumed in the literature.

Growing interest in free-space optical communication, due to the high bandwidth and security provided by these links, has generated the necessity of designing high-performance satellite terminals. In order to develop these terminals, the opto-thermo-mechanical phenomena that appear in the space environment and their effect on optical communication links have to be understood in detail. A review of the opto-thermo-mechanical phenomena occurring in spaceborne terminals is presented, describing the relevance of each of them. The methods found to compute the impact on the communication performance due to opto-thermo-mechanical phenomena are collected by building the bridge between the optical and communication performance parameters. Finally, techniques available to mitigate the detrimental effects of these phenomena are classified, and the relevant research challenges are identified.

Higher educational institutions have broadly adopted Collaborative Engineering Design (CED) activities to prepare students for complex problem-solving in multidisciplinary settings. These activities are non-linear and mediated by various social practices and tools. Therefore educators might struggle in facilitating the achievement of specific learning goals. Embodied cognition is an approach that explains non-linear behaviour through orgamism-environment interactions and might therefore provide educators with insights on how to prompt students towards desired actions in CED activities. According to embodied cognition, we learn through actions that emerge as a response to a problem (task) and environmental constraints. Educators can guide students’ behaviour by proposing tasks and adapting the environmental constraints of a learning situation, thus creating a field of promoted action. In this paper, we outline the progress of a design-based research in which insights from embodied cognition are implemented to promote desired student behaviour in CED activities. We report on the results of our problem-exploration phase. A systematic literature review and focus groups with students revealed that students are often hesitant to adopt new practices and tools that could potentially improve their collaborative design process. Next, we propose three theory-based design principles in which the task and environmental constraints are leveraged to foster the adoption of practices and tools and apply them to CED activities. Finally, we will share preliminary observations of the learning processes triggered by the designed activities and outline the directions for future research.

Spaceborne Global Navigation Satellite Systems (GNSS) receivers have become ubiquitous sensors for spacecraft navigation, especially in Low Earth Orbits (LEOs), often also supporting science endeavors or as acting dedicated science payloads. Due to the large number of space-capable GNSS receiver models available, spacecraft designers, as well as scientists, may find it difficult to have or gain an overview of suitable state-of-the-art models for their purposes and constraints. Based on a literature review that included more than 90 different receiver models, this paper aims to provide an overview of space-capable GNSS receivers that have a heritage in space missions. It analyses trends from the collected data and provides an outlook on miniaturized GNSS receiver models, which have a high potential of being used in future space missions.

This paper introduces an adaptive Convolutional Neural Network (CNN)-based Unscented Kalman Filter for the pose estimation of uncooperative spacecraft. The validation is carried out at Stanford's robotic Testbed for Rendezvous and Optical Navigation on the Satellite Hardware-In-the-loop Rendezvous Trajectories (SHIRT) dataset, which simulates vision-based rendezvous trajectories of a servicer spacecraft to PRISMA's Tango spacecraft. The proposed navigation system is stress-tested on synthetic as well as realistic lab imagery by simulating space-like illumination conditions on-ground. The validation is performed at different levels of the navigation system by first training and testing the adopted CNN on SPEED+, Stanford's spacecraft pose estimation dataset with specific emphasis on domain shift between a synthetic domain and an Hardware-In-the-Loop domain. A novel data augmentation scheme based on light randomization is proposed to improve the CNN robustness under adverse viewing conditions, reaching centimeter-level and 10 degree-level pose errors in 80% of the SPEED+ lab images. Next, the entire navigation system is tested on the SHIRT dataset. Results indicate that the inclusion of a new scheme to adaptively scale the heatmaps-based measurement error covariance based on filter innovations improves filter robustness by returning centimeter-level position errors and moderate attitude accuracies, suggesting that a proper representation of the measurements uncertainty combined with an adaptive measurement error covariance is key in improving the navigation robustness.

Contribution: This article presents a comprehensive overview of characteristics of educational designs of collaborative engineering design activities found in literature and how these characteristics mediate students' collaboration. Background: Engineers have to solve complex problems that require collaboration. In education, various collaborative engineering design activities have been implemented to prepare students for these professional practices. According to cultural historical activity theory (CHAT), educational activities can be described in terms of interrelated elements, i.e., subject, object, tools, rules, division of labor, and community, that influence learning outcomes. A key issue is how these elements mediate students' collaborative efforts and how they contribute to learning. Research Questions: 1) How is collaborative learning implemented in engineering design education? 2) How do the elements of CHAT and their interrelations mediate collaborative learning? and 3) What is the evidence that the implementation of collaborative learning contributed to the achievement of desired learning outcomes? Methodology: A systematic literature review following preferred reporting items for systematic review and meta-analyses protocols guidelines was conducted, including 111 articles published between 2011 and 2021. CHAT was used as analytical framework. Findings: Collaborative learning was implemented in engineering design activities to develop technical as well as nontechnical skills. For the CHAT elements, it was found that establishing a common object, rules for collaboration, and division of labor are essential for effective collaboration and can be enhanced through digital technologies (tools) and support from a community, for example, educators. Finally, results showed that there is evidence that described implementations contribute to learning. However, this evidence needs to be interpreted with care, due to methodological issues in some included articles.

The Delft University of Technology has been working on Delfi-PQ, a 3 P P ocketQube d eveloped b y Aerospace Engineering students during their education. The satellite, while being only 50x50x178 mm and having a mass of 545 g, shares the same problems and requirements of bigger satellites. This paper presents the design concept, development, and testing of Delfi-PQ to help other teams in their development. All the combined information will help to generate a big picture for institutions to start their own small satellite mission.