This decade has seen growing interest in Mars exploration. Advances in distributed systems, miniaturization and commoditization of space electronics and innovations in communications permit us to rethink the current paradigm of relying on a few heavy, slow and expensive high-tech rovers for Mars surface exploration. In this work, we address the demanding communication needs for a mission that deploys a swarm of uncontrolled wind-driven exploration rovers onto the martian surface. The concept for these lightweight, autonomous, ellipsoid ”Tumbleweed” rovers — named after the desert plant — is not new, and was studied and validated by NASA researchers decades ago. Recently, a new plan to turn the Tumbleweed mission into reality has been proposed to the ESA open space innovation platform (OSIP). The idea is to launch approximately 90 Tumbleweeds in one transfer vehicle and release them on the martian surface to survey the northern hemisphere of Mars over a mission duration of three months. Reliable communication is one of the key challenges for this mission. The rovers’ instruments, e.g. cameras, generate large volumes of data, and many rovers need to be served simultaneously. Furthermore, the tumbling motion on the martian surface constitutes unprecedented challenges in terms of antenna pointing for planetary exploration rovers. We present a trade-off analysis between direct to Earth communication and relayed communication using satellites orbiting Mars culminating in a baseline communication architecture for the Tumbleweed mission. For this purpose we model the kinematics of the Tumbleweed rovers and relay satellites w.r.t the Earth. A numerical simulation of all potential communication links over the full mission duration is conducted. The analysis shows that direct communication to Earth is infeasible due to the rolling motion of the rover. Hence, the relayed communication scenario is proposed, as it does not require a directional antenna on the Tumbleweed rovers. Therefore, we propose a constellation of three relay satellites in a circular, Earth-facing orbital plane around Mars, which communicate with the Tumbleweed rovers using the UHF frequency band. Commercial ground stations on Earth in Ka-band are used for the relay-ground link. The proposed communications architecture is estimated to achieve a raw data throughput of ě84Mbit per Tumbleweed rover per Sol. @en

In the last decades, there has been a steady adoption of digital online platforms as learning environments applied to all levels of education. This increasing adoption forces a transition in educational resources which has further been accelerated by the recent pandemic, leading to an almost complete online-only learning environment in some cases. The aim of this paper is to outline the methodology involved in setting up a framework for mapping course-specific data based on student activity to standard learning indicators, which will serve as an input to performance prediction algorithms. The process involves systematically surveying, capturing, and categorising the vast range of data available in digital learning platforms. The data are collected from two sample courses and distilled into five dimensions represented by the generic learning indicators: prior knowledge, preparation, participation, interaction, and performance. The data is weighted based on course development and teaching member’s perspectives to account for course-wise variations. The framework established will allow portability of prediction algorithms between courses and provide a means for meaningful and directed learner formative feedback. Two courses, both bachelor-level and worth 5 European Credits (ECs), that use several online learning platforms in their teaching tools have been chosen in this study to explore the nature and range of student interaction data available, accessible, and usable in a course. The first course is Electromagnetics II at Eindhoven University of Technology, and the second course is Electronics at Delft University of Technology. Both Universities are located in the Netherlands. This work is in the scope of a broader study to use such learning indicators with predictive algorithms to provide a prognosis on individual student performance. The findings in this paper will enable the realization of student performance prediction at a very early stage in the course.@en

Recently, an increase in distributed space systems and a rise in number of nodes in such systems is observed in numerous space applications, for example space-based interferometry. Such applications pose stringent demands on time synchronization which can be challenging to achieve for satellite networks that lack an absolute time reference source, as would be the case with networks beyond Earth orbit. In this paper, we propose a new class of frequency-based and multi-domain time synchronization and ranging algorithms applicable to anchorless mobile networks of asynchronous nodes. First, the Frequency-based Pairwise Least Squares (FPLS) that estimates clock skew and relative velocity under constant pairwise velocity assumption. Second, the Combined Pairwise Least Squares (CPLS) — a two step approach where first, skew and velocity are estimated using FPLS and then its results are fed into a reformulated time domain method to estimate offset and range. The proposed methods are applied to a case study to OLFAR — a spaceborne large aperture radio interferometric array platform for observing the cosmos in the frequency range from 0.3 MHz to 30 MHz to be stationed in the Lunar orbit. The results show that the proposed methods decrease communication and computation needs and can improve the clock synchronization performance for space-based interferometry.@en

The inter-satellite link (ISL) in swarm and constellation missions is a key enabler in the autonomy of the mission. OLFAR (Orbiting Low Frequency Array for Radio astronomy) is one such mission where 10 to 50+ nanosatellites are placed in the Lunar orbit and perform astronomical observations from the far-side of the moon. Each of the nanosatellite in the swarm would carry a receiver that performs observations between 0.3 - 30 MHz, which are the least explored frequency bands in radio astronomy, thus attracting a large scientific interest.
Observations in this frequency bands from Earth are highly challenging as the ionosphere is opaque to these frequency bands. Furthermore, RFI (Radio Frequency Interferences) generated on Earth makes it highly challenging to perform astronomical observations below 30MHz band. The impediments faced by Earth-based or near-Earth-based radio astronomy for these frequency bands is the motivation to perform measurements from the far-side of the moon.
The purpose of using a swarm of nanosatellites to perform low frequency observations is to enable the realization of long observation baselines and additionally, the effective aperture of observation increases with the number of satellites. For the swarm of nanosatellites to operate as a single aperture, it is very important to cross-correlate the information collected by each satellite and this is where the ISL becomes very crucial. Apart from exchanging data collected by the payload, other information such as attitude and timing information needs to be exchanged.
This work derived mission level requirements which would be used to define a suitable communication architecture for space-based radio astronomy missions such as OLFAR. The approach chosen for communication system for such a swarm mission will comprise of two types of ISL: High data-rate directional link that will be used to exchange payload date and low data-rate omni-directional link that will be used to exchange attitude, timing information and be used for localization, positioning and ranging of the nanosatellites in the swarm. This work will present link budgets to show the feasibility of the proposed communication architecture and derive the specs to further design the transceivers.@en

The frequency range below 30 MHz remains one of the last unexplored frequency ranges in radio astronomy However, Earth-based observations at these wavelengths are severely impeded, due to man-made radio frequency interference (RFI) and atmospheric opacity. To overcome this impediment, various space-based radio astronomy studies have been proposed in the past decade, notably the OLFAR (Orbiting low Frequency Antennas for Radio Astronomy) study, which proposed a satellite swarm for ultra-long wavelength observation. To realize this mission, various technological challenges of a satellite swarm are currently being addressed, particularly antenna design, navigation, communication, distributed processing, and overall system and mission design. Secondly, the RFI levels at various altitudes from Earth is currently unknown, which is a hindrance in general for radio astronomy. To this end, we propose the use of high-altitude ballooning experiments to validate OLFAR sub-systems in pseudo-representative conditions. Furthermore, these ballooning experiments will measure the RFI in the ultra-long wavelength spectrum at various altitudes from Earth. Our project is termed LOBE (Low-frequency observations using high-altitude Balloon Experiments), and in this paper, we present an overview of the science objectives, payload, and the technological and programmatic challenges of the LOBE project.

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A distributed space system (DSS) is an architecture with more than one spacecraft to achieve a common objective. A number of questions arise with respect to the characteristics and dynamics of distributed system in space. How fast is the system spreading? How are the elements within the system distributed? Is it tightly or loosely packed? What is the effect of perturbations on its absolute and relative dynamics? What are the chances of a collision within the system? There has not been much research in these areas concerning a DSS. In this paper, quantitative metrics are established that allow characterizing DSS and assisting in answering above questions.Key performance indicators for a DSS are identified as size or envelope of the cluster, a distribution measure, and a measure for collision. Determining the geometric system size is straightforward through numerical or analytical propagation methods. The focus of this paper will be on the other two metrics: a cluster distribution index (CDI) and a measure for collision probability within the system. The distribution index can be used to assess the effectiveness of DSS in meeting system requirements such as coverage and resolution. An n-dimensional grid-based numerical approach is used to evaluate CDI. The collisions analysis using line-integral method (CALM) is proposed as an effective and efficient approach to analyzing collision probability within DSS. Results show that the CDI is an effective indicator to assess the influence of perturbations, such as differential drag, on spatial distribution of the system. The CALM approach is three orders of magnitude faster than existing approaches that evaluate collision probability for non-linear motion.

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The Lunar Meteoroid Impact Observer (LUMIO) is one of the four projects selected within ESA’s SysNova competition to develop a small satellite or scientific and technology demonstration purposes to be deployed by a mothership around the Moon. Themission utilizes a 12U form-factor CubeSat which carries the LUMIO-Cam, an optical instrument capable of detecting light flashes in the visible spectrum to continuously monitor and process the meteoroids impacts. In this chapter, we will describe the mission concept and focus on the performance of a novel navigation concept using Moon images taken as byproduct of the LUMIOCam operations. This new approach will considerably limit the operations burden on ground, aiming at autonomous orbit-attitude navigation and control. Furthermore, an efficient and autonomous strategy for collection, processing, categorization, and storage of payload data is also described to cope with the limited contact time and downlink bandwidth. Since all communications have to go via a lunar orbiter, all commands and telemetry/data will have to be forwarded to/from the mothership. This will prevent quasi-real-time operations and will be the first time for CubeSats as they have never flown without a direct link to Earth. This chapter was derived from a paper the authors delivered at the SpaceOps 2018 conference.

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The Lunar Meteoroid Impact Observer (LUMIO) is a CubeSat mission to observe, quantify, and characterize the meteoroid impacts by detecting their flashes on the lunar farside. LUMIO is one of the two winners of ESA’s LUCE (Lunar CubeSat for Exploration) SYSNOVA competition, and as such it is being considered by ESA for implementation in the near future. The mission utilizes a CubeSat that carries the LUMIO-Cam, an optical instrument capable of detecting light flashes in the visible spectrum. On-board data processing is implemented to minimize data downlink, while still retaining relevant scientific data. The mission implements a sophisticated orbit design: LUMIO is placed on a halo orbit about Earth–Moon L2 where permanent full-disk observation of the lunar farside is made. This prevents background noise due to Earthshine, and permits obtaining highquality scientific products. Innovative full-disk optical autonomous navigation is proposed, and its performances are assessed and quantified. The spacecraft is a 12U form-factor CubeSat, with 22 kg mass. Novel on-board micro-propulsion system for orbital control, de-tumbling, and reaction wheel desaturation is used. Steady solar power generation is achieved with solar array drive assembly and eclipse-free orbit. @en

The Lunar Meteoroid Impact Observer (LUMIO) is a mission designed to observe, quantify, and characterize the meteoroid impacts by detecting their flashes on the lunar farside. Earth-based lunar observations are restricted by weather, geometric, and illumination conditions, while a lunar orbiter can improve the detection rate of lunar meteoroid impact flashes, as it would allow for longer monitoring periods. This paper presents the scientific mission of LUMIO, designed for the ESA SysNova LUCE competition, that resulted as the ex-aequo winner in the competition. LUMIO, a 12U CubeSat weighting approximately 20 kg, is expected to be deployed into a quasi-polar selenocentric orbit by a mother spacecraft, which also acts as communication relay. From a lunar high-inclination orbit, LUMIO will autonomously determine its trajectory to reach the Moon–Earth L2 point and perform the cruise phase. From the operative orbit, LUMIO will observe the lunar farside. When the lunar disk illumination is less than 50%, LUMIO autonomously performs the scientific task without direct coordination from Earth. Fully autonomous operations will include science, communication, and navigation. A similar concept can be re-used for a wide variety of future missions. The scientific mission will also be possible thanks to an innovative on-board data processing system, capable of drastically reducing the information to transmit to Earth. The camera, designed to capture the flashes and measure their intensity is, in fact, capable of generating 2.6 TB/day while only approximately 1 MB/day will need to be transmitted to Earth. Impact identification will be autonomous and only relevant information will be transmitted. A study at the ESA/ESTEC concurrent design facility has shown evidence of feasibility and that a CubeSat orbiting along an Earth–Moon L2 quasi-halo orbit is expected to bring a relevant contribution to lunar science and innovation to space exploration.@en

The Lunar Meteoroid Impacts Observer (LUMIO) is one of the four projects selected within ESA’s SysNova competition to develop a small satellite for scientific and technology demonstration purposes to be deployed by a mother ship around the Moon. The mission utilizes a 12U form-factor CubeSat which carries the LUMIO-Cam, an optical instrument capable of detecting light flashes in the visible spectrum to continuously monitor and process the meteoroids impacts. In this paper, we will describe the mission concept and focus on the performance of a novel navigation concept using Moon images taken as byproduct of the LUMIO-Cam operations. This new approach will considerably limit the operations burden on ground, aiming at autonomous orbit-attitude navigation and control. Furthermore, an efficient and autonomous strategy for collection, processing, categorization, and storage of payload data is also described to cope with the limited contact time and downlink bandwidth. Since all communications have to go via a Lunar Orbiter (mothership), all commands and telemetry/data will have to be forwarded to/from the mother ship. This will prevent quasi-real time operations and will be the first time for CubeSats as they have never flown so far from Earth. @en

The Earth–Moon system is constantly being bombarded by a significant number of meteoroids with different sizes and velocities. Observation of the lunar surface impacts will enable characterization of the lunar meteoroid flux, which is similar to that of the Earth, and provide more detailed information on meteoroid size, velocity, temporal and spatial distribution. The Lunar Meteoroid Impacts Observer (LUMIO) is a CubeSat mission at Earth–Moon L2 to observe, quantify, and characterise these meteoroid impacts by detecting their flashes on the lunar farside. LUMIO is one of the two winners of ESA’s LUCE (Lunar CubeSat for Exploration) SysNova competition, and as such is being considered by ESA for implementation in the near future. This paper will present the design of the LUMIO spacecraft that will host the payload to capture the meteoroid flashes. Key system specifications, trade-offs and consequent design iterations are presented. The final design yields a feasible spacecraft budget and a configuration that enables the LUMIO mission to be realized by 2023. The spacecraft is a 12U form-factor CubeSat, with a mass of less than 22 kg. A zero-redundancy and COTS based approach has been adopted for the spacecraft design. A strong emphasis has been placed on realizing high onboard autonomy. A novel and autonomous navigation strategy that uses optical observations of the Earth and the Moon is proposed for navigation around the Moon and beyond. The payload and navigation are the key drivers of the pointing requirements. Pointing requirements are achieved through reaction wheels, IMUs, star trackers, and fine sun sensors. A hybrid micro-propulsion system is included for orbital control, de-tumbling, and reaction wheel desaturation. Steady solar power availability is ensured with a one-axis solar array drive assembly in combination with an innovative attitude algorithm. Communication with Earth is through the Lunar Orbiter with a low-bandwidth UHF link, which places high constraints on the data throughput. An onboard payload data processor has been designed that compresses the science data to a fraction of the raw data with no loss of information. The paper will conclude with the key findings of a concurrent design review of the LUMIO spacecraft design that was performed at ESA/ESTEC’s Concurrent Design Facility (CDF). The major design changes are outlined along with a summary and discussion of the iterated design.@en

The repertoire of words in the English language to refer to groups of animals is quite fascinating to say the least – a congregation of alligators, an army of ants, a troop of baboons, a pride of lions, a train of camels, a destruction of cats, an intrusion of cockroaches, a mob of emus, a plague of insects, a drift of pigs, and so on. The intention of using such a wide range of terms is to associate an underlying emotion or meaning to the different kinds of groups. Therefore, without knowing much about choughs or goldfinches, one is more likely to appreciate a charm of goldfinches rather than a clattering of choughs. This thesis is about groups of small spacecraft – characterizing them and enhancing them. The aim of this thesis is to enable charms of CubeSats and prides of PocketQubes.@en

This paper aims at analysing the current capabilities of the NORAD Space Surveillance network, in particular focusing on very small objects in LEO. Spacecraft miniaturization has been pushing the limits and capabilities of small satellites so much that spacecraft as small as 5x5x5 cm have already been launched and even smaller ones are currently envisaged. A common remark is that these objects would be impossible to track with the available radar sensors and they would ultimately only be a threat to existing and future space assets. By analysing the objects in the NORAD catalog, we demonstrate that similar sized objects are currently tracked successfully. Covariance analysis of the available orbital elements is used to demonstrate orbital elements accuracies similar to bigger satellites. We demonstrate as well that measured cross-section is consistently over-estimated for very small objects equipped with VHF or UHF antennas actually showing that this could boost their radar reflectivity. This paper shows that objects smaller than 10 cm in side are trackable by current surveillance radars and do not pose a higher threat than other satellites, in case proper measures are taken.@en

This paper proposes a novel phase synchronization technique that enables beamforming with multiple resource-limited spacecraft in space and capitalizes on their spatial geometry. The proposed technique employs an external beacon to obviate the need for explicit time synchronization and reduces the accuracy requirements on localization. Results show that subcentimeter (subnanosecond)-level phase synchronization can be achieved with localization accuracy in the order of meters.@en