Intersatellite optical communication links will be crucial for the development of future global optical and quantum communication networks. Under the harsh space environment satellite optical terminals will suffer pointing jitter and wavefront errors. In this paper, the impact of the combination of these errors on the transmitter side is modeled. Combining the far-field diffraction patterns obtained through computational Fourier optics and the statistics of the pointing jitter, the received power statistics are derived numerically for different scenarios. The computational model is first used to evaluate the optimum nominal parameters of the transmitted beam. Then, several optical aberrations are added to the transmitted beam and their impact on the communication performance is evaluated through the average bit error rate.@en

This paper proposes a novel approach to improve the performance of free-space optical communication intersatellite links by combining fundamental Gaussian and higher-order Laguerre-Gaussian beams. We present a comprehensive mathematical model to analyze the system’s performance, including received power statistics, average bit error probability, and outage probability. To generate the desired beam profiles, we propose an optical system capable of creating a superposition of orthogonally polarized Laguerre-Gaussian beams that yield the far-field irradiance distributions that optimize the communication performance. Our theoretical analysis demonstrates that the combination of fundamental Gaussian and higher-order modes can significantly enhance system performance compared to conventional fundamental Gaussian beams. In some scenarios, the proposed approach offers savings on the order of 20% to 40% of the required transmitted power.@en

One of the most ambitious goals of modern astronomy is to uncover signs of extraterrestrial biological activity, primarily achieved through spectroscopic analysis of light emitted by exoplanets to identify specific atmospheric molecules. Most exoplanets are indirectly identified through techniques like transit or Doppler shift of the host star's flux. Long-term surveys have yielded statistical insights into the occurrence rates of different planet types based on factors such as radius/mass, orbital period, and the spectral type of the host star. Initial estimates of terrestrial planets within the habitable zone have also emerged. However, the difficulty of detecting light from these exoplanets leaves much unknown about their nature, formation, and evolution. As the number of rocky exoplanets around nearby stars rises, questions about their atmospheric composition, evolutionary trajectory, and habitability increase. Direct measurement of an exoplanet's atmospheric composition through its spectral signature in the infrared can provide answers. Measuring the infrared spectrum of these planets poses significant challenges due to the star/planet contrast and very small angular separation from their host stars. Previous research showed that space-based telescopes are mandatory, and unless large primary mirrors (>30m in diameter) can be sent into space, interferometric techniques become essential. Combining light from distant telescopes with interferometric techniques allows access to information at minimal angular separation, operating within the diffraction limit of individual telescopes. Successful demonstrations of on-ground nulling interferometry open a new era for such space-based missions. They are vital to sidestep and tackle these scientific questions. We recently initiated a new study with the European Space Agency to explore the design parameters and the performances related to an interferometric concept based on a single spacecraft and sparse multiple sub-apertures. Launch constraints are linked to the use of an Ariane 6 launch vehicle. Our parametric study covers a range of 1-4 m for the diameter of the telescope and a 10-60 m baseline. The most promising concept working in the infrared range (3-20μm) will be highlighted. This study is conducted by TUDelft in cooperation with KULeuven, CSL/ULiège, and Amos with the support of the European Space Agency. @en

The distribution and behavior of the vast accumulation of plastic waste in the oceans, often referred to as the 'plastic soup’, are heavily influenced by plastic debris coming from rivers and coastal areas. Currently, the location and dynamics of the oceanic ‘plastic soup’ is already well understood. However, the exact process behind the formation of this plastic soup remains incompletely comprehended. This knowledge gap can be linked, in part, to the absence of worldwide detailed spatiotemporal data collected from ground and space. This is specifically due to the lack of detection and imaging techniques with a high spatial and temporal resolution. To address this gap, an innovative concept is proposed based on
imaging spectroscopy. The goal is to address and further improve the observed spectral signatures of different plastics by imaging the observed scenery. In order to distinguish between these different kinds of plastics, a dedicated optical filtering system with a high resolution and revisit time has to be designed. Therefore, the concept is based on an Acousto-Optic Tunable Filter (AOTF), specifically designed for remote sensing and imaging. In order to achieve a high temporal resolution, being able to capture the evolution and movement of plastic in the oceans, a constellation of satellites are foreseen. Therefore, a low flying platform and deployable optics are introduced. Flying at 300 km altitude instead of a typical > 600 km for Earth observation satellites, reduces the required imaging aperture. @en

This paper shows the roadmap of the development of a deployable space telescope at Delft University of Technology and explores its applications, key innovations and the design of a small demonstrator. Deployable space telescopes allow for smaller stowed dimensions during launch and it is expected that increasing demand for Earth observation at a high temporal resolution enables large constellations for which the reduction in launch cost per telescope will eventually break even with the required investment. The long term development of deployable space telescopes at TU Delft foresees a primary mirror of up to 1.5 m and the measurements in the visual spectrum, the thermal infrared spectrum and specific spectral lines for trace gasses. The near term objective is to develop a small demonstrator performing wide-band monitoring in the thermal infrared spectrum. This demonstrator comprises of a fixed 30 cm primary mirror and a deployed secondary mirror and baffle. The stowed instrument has roughly half the volume of its deployed configuration. Currently, critical technologies are being designed and proto-typed. The M2 is deployed and suspended by three carbon-fiber booms with custom-designed hinges and actuators at its root. Different configurations have been tested on their correct and accurate deployment.@en

This chapter provides an overview of the command and data handling system (CDHS) in small satellites and CubeSats. The chapter presents first analysis of radiation effects, specifically targeted at this subsystem, to justify components and architecture choices. Improvements in radiation testing strategies are also presented, specifically for small satellites. State-of-the-art components are then presented, providing an overview of the current market and the most common architectures. An overview of past and current missions is also presented, providing a clear mapping of the presented state-of-the-art components and architectures to guide future designs. High-level design considerations are also presented to help the reader follow some of the current trends in the sector. This chapter, overall, aims at presenting the most common approaches for the CDHS system and comparing this with traditional satellites, showing where the main differences lay with component selection and testing strategies being the fundamental points driving the architecture choices.

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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.@en

The objective of this paper is to investigate which approach would lead to more reliable CubeSats: full subsystem redundancy or improved testing. Based on data from surveys, the reliability of satellites and subsystems is estimated using a Kaplan–Meier estimator. Subsequently, a variety of reliability models is defined and their maximum likelihood estimates are compared. A product of a Lognormal distribution addressing immaturity failure and a Gompertz distribution addressing wear-out is found to best represent CubeSat reliability. Bayesian inference is used to find realistic wear-out parameters by using failure data of small satellites. Subsystem reliability estimates are subsequently found using a similar approach. A reliability model for CubeSats with redundant subsystems is established, verified and applied in a Monte Carlo simulation. The results are compared with a model for reduced immaturity failure. Allocating resources to reduction of immaturity failures through improved testing is considered to be superior to allocating these resources to the implementation of subsystem redundancy.@en

This thesis provides an innovative architecture for CubeSats and PocketQubes to improve their performance and reliability. CubeSats and PocketQubes are standard satellite form factors composed of one or more cubic units of 10 cm and 5 cm respectively. It is found that the current modular subsystem approach and the electrical interfaces are not optimal in terms of performance and use of technical resources. Reliability is also a concern for CubeSats. Only 35% are able to achieve full mission success. Available literature provides no comprehensive studies on these matters and there is thus a gap in knowledge to be filled. The objective of this study is to identify and quantify the performance and reliability issues related to the physical arrangement of subsystems and the electrical interfaces and to develop an innovative bus architecture which is reliable, flexible and allows for increased performance. The overarching research question is: ”Which satellite bus architecture provides a reliable solution to the needs and constraints of a CubeSat and a PocketQube mission?” @en

PocketQubes are a form factor of highly miniaturized satellites with a body of one or more cubic units of 5 cm. In this paper, the characteristics of PocketQubes in terms of their constraints and their (potential) utility are treated. To avoid space debris and limit collision risk, the orbits of PocketQubes need to be constraint. An analysis of orbital decay characteristics has been carried out which, considering existing space regulations and a pro-active attitude, PocketQubes should preferably be launched in low Earth orbits below 400 km altitude. Due to technical constraints, such as form factor, power and attitude control, the domain of applications for single PocketQube missions is limited. Still, they can act as low-cost training and technology demonstration platforms. To make PocketQubes an attractive platform for other types of missions, not only the launch cost, but also the development, production and operations cost should be significantly lower than CubeSats. When the PocketQube platform matures and produced in high numbers, networks of PocketQubes can enable new applications. Applications considered feasible are in the field of (but not limited to) continuous surveillance using optical instruments, gravity field monitoring using precise orbit determination, in-situ measurements of the space environment, low data rate or bandwidth communication services and inexpensive probes around other celestial bodies.

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This paper presents the design of a multi-frequency deployable antenna system for femto-satellites as part of the Delfi-PQ project, a PocketQube with a size of 50x50x178 mm which is being developed by the Delft University of Technology. This new form factor brings its own challenges on every subsystem and it is seen as a stepping stone towards even more miniaturised satellites. In this paper we present the design trade-offs, the analysis and the and measurements on the antenna system. The system is designed to operate in 4 different bands to guarantee communications and payload operations. Due to the very limited available space on the external faces of the spacecraft, it was decided to deploy all the antennas and multiplex the different bands on the available antenna elements. VHF and UHF are used for satellite telemetry and commanding while a dual-frequency GPS receiver is intended as payload. The satellite design is presented, together with design drivers for such a system to justify the design choices. Three RF configurations are analysed and compared for omni-directional coverage and peak gain. RF measurements on one of the configurations is also presented to validate the simulations. The deployment system is also presented, giving details on the design and expected tests to complete the qualifications.@en

PocketQubes represent a new type of cube-shaped platforms with dimensions of 50x50 mm and mass of 250 g. Just like the CubeSats, these platforms are also split in units which are referred to as 1P. The Delft University of Technology has been working on Delfi-PQ, a 3P PocketQube with the dimensions of 50x50x178 mm. This miniaturized size brings its own challenges on every subsystem. In this paper, structural design, integration and kill switch mechanisms will be explained.@en

The recent developments in space exploration have reinstated the Moon as a primary target for near future space missions. The principal reasons include the Moon being the closest test bed and analogue for planetary space missions and the prospect of scientific lunar bases and orbital stations within the next decade. Previous space missions have vastly improved our understanding on hazards of human spaceflights but not fully regarding the threats affecting a prospective lunar base or orbital station. The micrometeorite hazard has been partially addressed as an issue which can potentially impact both astronauts' health and safety as well as create issues for lunar bases and orbital stations, such as degradation or permanent damage of equipment and facilities. The current understanding is based partly on dust and micrometeoroid flux measurements and impact flash observations. However, observations with improved spatial and temporal resolution are imperative for advancing existing hazard models. In this paper, a mission concept of a constellation of nanosatellites is proposed that can both observe larger parts of cis-lunar and trans-lunar space while providing higher temporal resolution. Nanosatellite missions are a cost-effective solution providing data for significant improvement of our current understanding of lunar micrometeoroid flux models, and thus directly the scale of hazards caused by micrometeoroid impacts to future lunar missions. Additionally, such a distributed constellation mission will offer countless opportunities for academia, students and young scientists worldwide. The mission concept (Moon Compact Satellite for Hazard Assessment - MOOCHA) is a result of the Nordic-European Astrobiology Campus Summer School 2018 themed “Microsatellites in Planetary and Atmospheric Research” and was further developed during the 2019 follow-up summer school “Design of Small Satellite Missions for Planetary Studies”, both taking place in Tartu, Estonia and co-organized by the Stockholm University Astrobiology Centre, the University of Tartu, the European Astrobiology Campus and the Nordic Network of Astrobiology and supported by European Union's European Regional Development Fund and Estonia.@en

PocketQubes are a new form factor of highly miniaturized satellites with a body of one or more cubic units of 5 cm. The characteristics of PocketQubes in terms or legal and regulatory aspects, the technological readiness levels and financial considerations are assessed. In particular, an analysis of orbital decay characteristics has been carried out which together with existing space law suggest that PocketQubes should preferably be launched in very low Earth orbits below 500 km altitude. To make PocketQubes attractive platforms, not only the launch cost, but also the development, production and operations cost should be significantly lower than CubeSats . Due to technical constraints, such as form factor, power and attitude control, the domain of applications is, especially for single PocketQube mission constrained. Still, they can act as low cost training or technology demonstration platforms. When launched in high numbers, networks of PocketQubes can enable new applications for Earth observation and niche communication services. Applications considered feasible are in the field of (but not limited to) continuous surveillance using optical instruments, gravity field monitoring using precise orbit determination, in-situ measurements of the space environment and low data rate or bandwidth communication services.@en

Delft University of Technology has embarked on PocketQubes to showcase as the next class of miniaturized satellites. In the past decade, CubeSats have grown towards a successful business with mature capabilities. PocketQubes, however, are still in their infancy. The small size of the PocketQubes will trigger innovations in miniaturization and will force one to think differently about space technology. It is not sufficient to simply down-scale existing concepts used in CubeSats, there is a necessity to develop and qualify completely new components through which new applications can be enabled in the future. The new satellite platform, called Delfi-PQ, inspired by the success of previous Delfi satellite projects is seen as an opportunity for innovation and offers research challenges in the miniaturization field of systems and components. The focus of this paper is to highlight those innovations and challenges, and to communicate the progress that has been made with respect to building a core platform and standardized bus. The mission of Delfi-PQ is to demonstrate a reliable core bus and outer structure for a three unit PocketQube that shall be tested in flight as a first iteration of a series of PocketQubes to be developed by Delft University of Technology. The core bus shall fit in one unit - 1P (50x50x50mm), having as aim that after further miniaturization and optimization, the second unit shall contain an advanced subsystem (e.g. advanced Attitude Determination and Control System - ADCS) and the third unit shall consist of a scientific payload (e.g micro-propulsion, lensless camera). For Delfi-PQ, the focus was on the miniaturization process and on the structure of the PocketQube. The core platform of the first Delfi-PQ consists of the Electrical Power System (including two 3.7V batteries and solar panels with two cells/each X-Y face), On-board Computer, Communications System, ADCS (including two magnetorquers and three magnetometers), as well as: temperature sensors and two different sensors for assessing the rotational speed of the PocketQube.@en

Developers experience issues with the compatibility, connector size and robustness of electrical interface standards for CubeSats and PocketQubes. There is a need for a lean and robust electrical interface standard for these classes of satellites. The proposed interface standard comprises a linear data bus which is used for housekeeping data, internal commands and small-to-moderate payload data. A community based analytic hierarchy process is used for the trade-off of design options, resulting in the selection of RS-485 as standard data bus, mainly due to its low power consumption and high effective data throughput compared to other candidates. Several switched and protected battery voltage lines are distributed from the central electrical power subsystem unit to the other subsystems to enable a simple and efficient power distribution. The harness comprises a 14 and 9 pin stackable connector for CubeSats and PocketQubes, respectively, occupying very little board space.@en

The dominant architectural approach in CubeSats and PocketQubes is the use of modular physical units, each hosting (part of the) components of classical (virtual) subsystems. Many of these small satellites, however, also host subsystems or experiments with slightly alternative approach, e.g. with cellularization of components or the integration of functions from different virtual subsystems into a single physical unit. These concepts also have been investigated and proposed by some studies on a much more rigorous implementation. Cellularization of complete satellite segments, the implementation of artificial stem cells, a satellite which comprises only of outer panels and plug-and-play technology are examples of these advanced concepts. While they offer promising advantages when implemented smartly as part of a new architecture, their disadvantages become dominant when such a concept is implemented in a too rigorous and dogmatic manner. A smartly chosen hybrid of several concepts is investigated. An advanced outer but flat panel mixes the cellularized concept and integrates many components which interact with the outside world. Internally, modular systems are still used, but some classical core subsystems can be integrated towards a single core unit. A lean approach on redundancy and electrical interfaces saves volume (for more payload volume or smaller satellites) and reduces overall systems complexity. The overall impact on reliability is expected to be positive when taking development and testing time into account, but this requires more in-depth study to be validated. @en

For many years, traditional satellite design philosophy was dominated by highly reliable components, conservative designs and extensive performance testing at subsystem and integrated system levels to achieve long lifetimes in the harsh space environment. CubeSats attempted to choose a different philosophy, utilizing suitable state-of the art, commercial-off-the shelf products, yielding, if successful, an increased performance per mass figure of merit for those small vessels at potentially higher risk but lower cost. CubeSats seemed to promise universities and companies to be faster, better and cheaper - once more in history. Unfortunately, many CubeSat missions, especially university-built ones, never achieved a detectable functional state or failed shortly after the satellites were ejected from their deployer. Data based on our developed CubeSat Failure Database (CFD) and research carried out by others suggest, that a great percentage of those early failure cases could have been detected and avoided by more careful and adequate system-level functional testing on the ground. However, many university teams still fail to plan with adequate resources for system level functional testing or are confronted with hard deadlines, thus unable to complete appropriate integrated system testing on a sufficient level, and launching a satellite that never was adequately functional. Ongoing work on a novel reliability estimation tool using Bayesian methods is introduced to fill this gap and to provide meaningful data for all developers on the achievable reliability and required functional testing time of their CubeSats. Using test data and reliability goals for their actual mission, merging that data with statistical data from past missions and a database of subjective developer's beliefs, CubeSat developers should now be able to estimate their required functional testing time on subsystem and system level at an early project stage, as a function of the targeted reliability goal for their CubeSat. Alternatively, if the required resources (testing time, money, knowledge) are not available, CubeSat developers and program managers can still use the tool to now quantify a resulting realistic lower boundary for the expected system reliability of the mission, and decide, if their mission goals can be fulfilled or not with a certain probability. To evolve CubeSats into more reliable and accepted platforms for scientific payloads and commercial applications, it is utmost important to avoid or reduce the many infant mortality cases, where no or little useful data is produced by the satellite. To guide developers towards higher success rates without losing the spirit of using novel, state of the art technology in fast mission timelines, the reliability estimation tool should ensure higher reliability of CubeSat missions without drawing too much resources nor imposing too many burdens on the CubeSat teams.

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A miniaturized reaction wheel suitable for picosatellites (<1 kg) has been developed for Delft University of Technology's PocketQube (PQ) mission. Delfi-PQ aims to demonstrate a reliable core bus platform for PocketQubes with a form factor of 5x5x5 cm and one or more payload(s). Continuing trends in miniaturization of technology, PocketQubes hold the potential to further reduce the cost of access to space and disrupt traditional space applications by providing cost effective global coverage. Three-axis stabilization is required for advanced capabilities such as Earth observation, high data rate transfers and propulsive manoeuvres. Precise attitude control requires reaction wheels with highly accurate speed control and low vibration levels. Power and volume requirements, however, drive a simple and compact design. A reaction wheel assembly with a mass of 7 g, maximum steady state power consumption of 25 mW and size of 18x10x11.5 mm has been designed, integrated and tested. A simple flywheel is attached to a brushless electric motor and secured in a pressurised housing. The reaction wheel can provide at least a torque of 3 ∗ 10-7 Nm over its full speed range and has a (one way) momentum storage of 1.1 ∗ 10-4 Nms. This is sufficient for attitude stabilization and ground station tracking on a triple-unit PocketQube in a 360 km Low Earth Orbit. Functional, performance, environmental and micro-vibration tests have been performed. Strict power requirements led to an in-depth analysis of the power consumption of the reaction wheel assembly. A Simulink model of the motor including control electronics models was used to characterize the power consumption. Results indicate the feasibility of using reaction wheels on picosatellites with improvements to the flywheel balance and sealing efficacy of the housing required for long-term performance. A proposed three-wheel assembly design was created measuring only 31x31x22 mm including control electronics. Once completed, world's smallest reaction wheel (assembly) is expected to be launched as part of the attitude control subsystem on the Delfi-PQ mission to demonstrate and characterize its performance under true space conditions.@en