Enhanced Distributed Space Systems with Miniature Spacecraft: Spatial Distribution, Collision Analysis and Cooperative Communication

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.ElectronicsSpace Systems Egineerin

Frequency Augumented Clock Synchronizaion for Space-based interferometry

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

A Novel Planar Antenna for CubeSats

The UHF radio amateur band situated around 436 MHz is a very popular radio band for CubeSat Communications. This band has around 14.5 dB lower path loss compared to the popular S-band due to the lower frequency. The longer wavelength accompanied with the UHF band results in antennas that are relatively big compared to the size of a CubeSat. To communicate in this band, CubeSats are therefore equipped with linear wire antennas in dipole or turnstile configuration. Compared to patch antennas which are used to communicate in the S-band, these linear wire antennas have the downside that they need a deployment mechanism. This deployment mechanism increases the risk of failure during the mission, and subsequently asks more attention during design, integration and testing of the CubeSat. Furthermore, this system adds extra mass to the CubeSat and it takes up space that could be used by other subsystems. A novel planar antenna is proposed in this paper that obviates the need for deployment and meets most of the communication requirements for a CubeSat.To resolve the issues associated with a wire antenna requiring deployment, research was conducted to use a patch antenna to communicate in the UHF band. Conventional patch antennas that are resonant at 436 MHz proved to be too big to integrate in a CubeSat body. The planar inverted F antenna (PIFA) with it small form factor with respect to the operating frequency was identified as a suitable antenna choice for CubeSats. The electromagnetic simulation software FEKO has been used to successfully simulate a PIFA. Results indicate that the antenna is resonant at 436 MHz and fits on a 3U CubeSat body. The simulated antenna has a low profile height of only 3mm such that it still fits in a CubeSat launch POD. The radiation pattern is similar to the radiation pattern of a dipole antenna with a maximum gain of 3.72 dBi and a bandwidth of 2.82MHz is obtained. The use of such a PIFA antenna with no deployment mechanisms and with potential to be integrated as part of the CubeSat structure, promises further benefits and opportunities for future CubeSat missions.Space Systems Egineerin

Communications architecture for Martian surface exploration with a swarm of wind-driven rovers

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

Two CubeSats with Micro-Propulsion in the QB50 Satellite Network

A network of small low-cost satellites is the only realistic option for multi-point in-situ measurements in the lower thermosphere. The QB50 program, an initiative of the von Karman Institute of Fluid Dynamics (VKI), aims to employ a network of 50 CubeSats built by universities to study the lower thermosphere (90-320 km). All 50 CubeSats will carry identical sensors and will be launched together from a single launch vehicle. QB50 will also study the re-entry process by measuring a number of critical parameters during re-entry. The Delft University of Technology (TUDelft) intends to provide two satellites out of the 50 CubeSats in the QB50 network. This paper will discuss the preliminary orbit analysis of the QB50 satellites that will allow a first order evaluation of mission performance parameters like lifetime and coverage. The paper will subsequently look at the two satellites provided by TUDelft, each of which is equipped with a highly miniaturized propulsion system in addition to the science payload. This scenario is an excellent opportunity to demonstrate relative motion control between two CubeSats and elevate university CubeSats as serious contenders for significant science missions. A first analysisassesses the possibility of drag compensation and differential drag compensation using the TUDelft satellites with micro-propulsion

Systematic identification of applications for a cluster of femto-satellites

Embracing reduced requirements and leveraging commercial technology has led to a fast growing small satellite industry. Although most interest in small satellites has hovered around the micro satellites through to the picosatellites, academic interest now extends up to the sub 100 g range of satellites as well. Femto-satellites with a mass range between 10 g and 100 g could in the future be mass produced and hundreds to thousands of femto-satellites can be deployed as a cluster to enhance, for example, the situational awareness of the Earth’s environment. Femto-satellite is seen to form the next class of miniature satellites which will exploit spacecraft engineering, swarm science and mission design to realize exciting new space missions. Consequently, there has been considerable research interest in the sub 100 g range of satellites and the advantage of distributed satellites in space. However, most of the research work has been limited to a bottom-up approach to realize an individual femto-satellite with as much functionality as possible, without sufficient attention to the realization of an application using these distributed femto-satellites in space. This has resulted in an ambiguous top tier of space applications whose realization with a cluster of femto-satellites is arguable. The paper outlines the different realizations of distributed systems in space and identifies the most suitable candidate for femto-satellites. The aim is to map the user requirements for applications to the scaled capability of a cluster of femto-satellites, thereby aiding to systematically identify potential applications for femto-clusters. The principal challenge is that there exists no simple means to scale the capability of an individual femto-satellite to the capability of a distributed cluster of femto satellites. Scaling certain capabilities is not straightforward. For example, when we consider a user requirement such as orbit control, the inherent virtue of a distributed system may obviate the need for orbit control in individual satellites for some scenario and may not in other cases. These functionalities are carefully considered to develop a qualitative approach that will enable the scaling of individual satellite capability to the overall capability of a cluster of satellites.Delft University of Technolog

Frequency Augumented Clock Synchronizaion for Space-based interferometry

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.ElectronicsSignal Processing System

Long-term performance analysis of NORAD Two-Line Elements for CubeSats and PocketQubes

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 thatobjects 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.Space Systems EgineeringSpace Engineerin

Communications architecture for Martian surface exploration with a swarm of wind-driven rovers

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.Signal Processing System

LUMIO: Characterizing Lunar Meteoroid Impacts with a CubeSat

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