Future space telescopes with diameter over 20 m will require new approaches: either high-precision formation flying or in-orbit assembly. We believe the latter holds promise as a potentially lower cost and more practical solution in the near term, provided much of the assembly can be carried out autonomously. To gain experience, and to provide risk reduction, we propose a combined mico/nano-satellite demonstration mission that will focus on the required optical technology (adaptive mirrors, phase-sensitive detectors) and autonomous rendezvous and docking technology (inter-satellite links, relative position sensing, automated docking mechanisms). The mission will involve two "3U" Cubesat-like nanosatellites ("MirrorSats") each carrying an electrically actuated adaptive mirror, and each capable of autonomous un-docking and re-docking with a small central "15U" class micro/nano-satellite core, which houses two fixed mirrors and a boom-deployed focal plane assembly. All three spacecraft will be launched as a single
Sorensen TC, Bergman JES, Saunders C, Gao Y, Lappas V, Liddle D, Mouginis-Mark P, Nunes MA, Palmer P, Underwood C, Bridges C (2014) Using a constellation of small satellites to characterize the RF quiescence of the lunar farside, Proceedings of the International Astronautical Congress, IAC 6 pp. 4071-4083
Radio images of red-shifted 21-cm signals from neutral hydrogen originating from the very early Universe, the so-called Dark Ages before the first stars formed, are impossible to obtain from Earth due to man-made radio frequency interference (RFI) and the opacity of the ionosphere below
With the space shuttle on the eve of its final mission, British companies are at the forefront of innovation to drive the next wave of space exploration
While small, low-cost satellites continue to increase in capability and popularity, their reliability remains a problem. Traditional techniques for increasing system reliability are well known to satellite developers, however, their implementation on low-cost satellites is often limited due to intrinsic mass, volume and budgetary restrictions. Aiming for graceful degeneration, therefore, may be a more promising route. To this end, a stem-cell-inspired, multicellular architecture is being developed using commercial-off-the-shelf components. It aims to replace a significant portion of a typical satellite?s bus avionics with a set of initially identical cells. Analogous to biological cells, the artificial cells are able to differentiate during runtime to take on a variety of tasks thanks to a set of artificial proteins. Each cell reconfigures its own proteins within the context of a system-wide distributed task management strategy. In this way, essential tasks can be maintained, even as system cells fail. This paper focusses on two hardware implementations of the stem-cell inspired architecture. The first implementation, based on a single cell, serves as the Payload Interface Computer on a CubeSat named SME-SAT. The second hardware implementation is a benchtop system composed of several cells intended to demonstrate a complete multicellular system in operation. In order to demonstrate the feasibility of these multicellular architectures, the physical attributes of the hardware implementations are compared to those of more traditional implementations and are shown to have enhanced reliability at the cost of increased power and internal bus bandwidth.
The ongoing evolution in constellation/formation of CubeSats along with steadily increasing number of satellites deployed in Lower Earth Orbit (LEO), demands a generic reconfigurable multimode communication platforms. As the number of satellites increase, the existing protocols combined with the trend to build one control station per CubeSat become a bottle neck for existing communication methods to support data volumes from these spacecraft at any given time. This paper explores the Software Defined Radio (SDR) architecture for the purposes of supporting multiple-signals from multiple-satellites, deploying mobile and/or distributed ground station nodes to increase the access time of the spacecraft and enabling a future SDR for Distributed Satellite Systems (DSS). Performance results of differing software transceiver blocks and the decoding success rates are analysed for varied symbol rates over different cores to inform on bottlenecks for Field Programmable Gate Array (FPGA) acceleration. Further, an embedded system architecture is proposed based on these results favouring the ground station which supports the transition from single satellite communication to multi-satellite communications.
The current trend in commercial processors is producing multi-core architectures which pose both an opportunity and a challenge for future space based processing. The opportunity is how to leverage multi-core processors for high intensity computing applications and thus provide an order of magnitude increase in onboard processing capability with less size, mass, and power. The challenge is to provide the requisite safety and reliability in an extremely challenging radiation environment. The objective is to advance from multiple single processor systems typically flown to a fault tolerant multi-core system. Software based methods for multi-core processor fault tolerance to single event effects (SEEs) causing interrupts or ?bit-flips? are investigated and we propose to utilize additional cores and memory resources together with newly developed software protection techniques. This work also assesses the optimal trade space between reliability and performance. Our work is based on the modern compiler ?LLVM? as it is ported to many architectures, where we implement optimization passes that enable automatic addition of protection techniques including Nmodular redundancy (NMR) and error detection and correction (EDAC) at assembly/instruction level to languages supported. The optimization passes modify the intermediate representation of the source code meaning it could be applied for any high level language, and any processor architecture supported by the LLVM framework. In our initial experiments, we implement separately triple modular redundancy (TMR) and error detection and correction codes including (Hamming, BCH) at instruction level. We combine these two methods for critical applications, where we first TMR our instructions, and then use EDAC as a further measure, when TMR is not able to correct the errors originating from the SEE. Our initial experiments show good performance (about 10% overhead) when protecting the memory of code using double error detection single error correction hamming code and TMR (Triple modular redundancy), further work is needed to improve the performance when protecting the memory of code using the BCH code. This work would be highly valuable, both to satellites/space but also in general computing such as in in aircraft, automotive, server farms, and medical equipment (or anywhere that needs safety critical performance) as hardware gets smaller and more susceptible.
Continual advancements in Earth Observation (EO) optical imager payloads has led to a significant increase in the volume of multispectral data generated onboard EO satellites. As a result, a growing onboard data bottleneck need to be alleviated. One technique commonly used is onboard image compression. However, the performance of traditional space qualified processors, such as radiation hardened FPGAs, are not able to meet current nor future onboard data processing requirements. Therefore, a new high capability hardware architecture is required. In previous work a new GPU accelerated scalable heterogeneous hardware architecture for onboard data processing was proposed. In this paper, two new CUDA GPU implementations of the state-of-the-art lossless multidimensional image compression algorithm CCSDS-123, are discussed. The first implementation is a generic CUDA implementation of the CCSDS-123 algorithm whilst the second is optimised specifically for multispectral EO imagery. Both implementations utilise image tiling to leverage an additional axis for algorithm parallelisation to increase processing throughput. The CUDA implementation and optimisation techniques deployed are discussed in the paper. In addition, compression ratio and throughput performance results are presented for each implementation. Further experimental studies into the relationships between algorithm user definable compression parameters, tile sizes, tile dimensions and the achieved compression ratio and throughput, were performed.
The European Student Earth
Orbiter (ESEO) is a micro-satellite mission
to low Earth orbit and is being developed,
integrated, and tested by European
university students as an ESA Education
Office project. AMSAT-UK and Surrey
Space Centre are contributing to the mission
with a transceiver and transponder similar
to that of FUNcube-1 with the addition
of utilising a Atmel AT32 processor for
packet software-redundancy, baseband
processing, forward error correction, and
packet forming; acting as a step towards
software defined radio using low MIPS
automotive microprocessors. As on the
FUNcube-1 satellite, the telemetry formats
and encoding schemes presented utilize a
large ground network of receivers on the
VHF downlink and conforms to 1200 bps
and a new 4800 bps redundant downlink
for the rest of the spacecraft. The uplink is
on L-band using bespoke partial-CCSDS
The European Student Earth Orbiter (ESEO) is a micro-satellite mission to Low Earth Orbit and is being developed, integrated, and tested by European university students as an ESA Education Office project. AMSAT-UK and Surrey Space Centre are contributing to the mission with a transceiver and transponder similar to that of FUNcube-1 with the addition of utilising a Atmel AT32 processor for packet software-redundancy, baseband processing, forward error correction, and packet forming; acting as a step towards software defined radio using low MIPS automotive microprocessors. As on the FUNcube-1 satellite, the telemetry formats and encoding schemes presented utilize a large ground network of receivers on the VHF downlink and conforms to 1200 bps and a new 4800 bps redundant downlink for the rest of the spacecraft. The uplink is on L-band using bespoke partial-CCSDS frames. This paper details the flight software on the engineering and flight models to ESA, and the technical configuration and associated tests of demonstrating the processor load is under for varying operating and sampling modes. In particular, a key contribution will be the details of utilising the Google Test Suite for verification of the SDR functions and FreeRTOS tools to optimize processor load margins to 30% when operating parallelized ADC and DAC, and CAN-open telemetry chains and what memory considerations are needed to ensure stable long-term operations.
Proximity flight systems for rendezvous-and-docking, are traditionally the domain of large, costly institutional
manned missions, which require extremely robust and expensive Guidance Navigation and Control (GNC) solutions.
By developing a low-cost and safety compliant GNC architecture and design methodology, low cost GNC solutions
needed for future missions with proximity flight phases will have reduced development risk, and more rapid
development schedules. This will enable a plethora of on-orbit services to be realised using low cost satellite
technologies, and lower the cost of the services to a point where they can be offered to commercial as well as
institutional entities and thereby dramatically grow the market for on-orbit construction, in-orbit servicing and active
debris removal. It will enable organisations such as SSTL to compete in an area previously exclusive to large
institutional players. The AAReST mission (to be launched in 2018), will demonstrate some key aspects of low cost
close proximity ?co-operative? rendezvous and docking (along with reconfiguration/control of multiple mirror
elements) for future modular telescopes. However this is only a very small scale academic mission demonstration
using cubesat technology, and is limited to very close range demonstrations.
This UK National Space Technology Programme (NSTP-2) project, which is being carried out by SSTL and SSC, is
due to be completed by the end of November 2017 and is co-funded by the UK Space Agency and company R&D. It
is aiming to build on the AAReST ("Autonomous Assembly of a Reconfigurable Space Telescope") mission (where
appropriate), and industrialise existing research, which will culminate in a representative model that can be used to
develop low-cost GNC solutions for many different mission applications that involve proximity activities, such as
formation flying, and rendezvous and docking. The main objectives and scope of this project are the following:
· Definition of a reference mission design (based on a scenario that SSTL considers credible as a realistic
scenario) and mission/system GNC requirements.
· Develop a GNC architectural design for low cost missions applications that involve close proximity
formation flying, rendezvous and docking (RDV&D) - i.e. ?proximity activities?
· Develop a low cost sensor suite suitable for use on proximity missions
· Consider possible regulatory constraints that may apply to the mission
The SSTL/SSC reference mission concept is a
While small, low-cost satellites continue to increase in capability and popularity, their reliability remains a problem. Traditional techniques for increasing system reliability are well known to satellite developers. They include the use of radiation-hardened and screened components, extensive cold redundancy and thorough test campaigns. However, the implementation of these techniques on small, low-cost satellites is often limited due to intrinsic mass, volume and budgetary restrictions. Aiming for graceful degradation, therefore, may be a more promising route.
Inspired by the robustness of single-celled and multi-cellular biological organisms, bio-inspired computing systems, multi-agent systems, and modular spacecraft concepts, this work presents the design, implementation and analysis of an artificial, cell-based system architecture. Named the Satellite Stem Cell Architecture, the proposed system aims to replace a significant portion of a typical satellite?s bus avionics with a set of initially identical, mass produced, artificial cells. Analogous to their biological counterparts, the artificial cells can differentiate during runtime to take on a variety of tasks, thanks to a set of artificial proteins. Each cell reconfigures its own proteins within the context of a system-wide, distributed task management strategy. In this way, essential tasks can be maintained, even as system cells fail.
The Satellite Stem Cell Architecture differs from existing bio-inspired computing systems by extending the concept to include reconfigurable interfaces to real-world sensors and actuators, and by its inclusion of a set of middleware which turns each cell into a multi-agent platform. Furthermore, an emphasis is placed on practical applicability, with power consumption, volume and production cost driving the implementation. A detailed description of the artificial cell hardware, and multi-agent middleware, is given. Additionally, two CubeSat-scale, practical implementations of the architecture are described. While one, which forms the payload interface computer of the SMESAT CubeSat, demonstrates only a subset of the proposed multicellular features, the other is a full testbed based on two artificial cells of four proteins each.
To compare the reliability of the proposed architecture to traditional forms of redundancy, an analytical reliability equation is derived for predicting the lifetimes of multicellular systems. It is shown that determining the optimal configuration of proteins per cell and cells per system is complex, as different configurations are optimal during different phases of the mission lifetime. Nevertheless, a set of trends in system behaviour are discovered, which will prove useful to system designers. Using a purpose-developed, multicellular simulation environment, the results of the analytical work are verified, and further problems relating to peripheral interfaces and cross-strapping are investigated.
Finally, using measured characteristics of the implemented testbed and the derived analytical lifetime predictions, the Artificial Stem Cell Architecture is compared against traditional CubeSat and microsatellite avionics suites. The results show that the proposed architecture gives increasing reliability and performance benefits with increased scale, and that while its power consumption overheads make it prohibitive for implementation on CubeSats, it is well-suited to microsatellites.
Significant advances in spaceborne imaging payloads have resulted in new big data problems in the Earth Observation (EO) field. These challenges are compounded onboard satellites due to a lack of equivalent advancement in onboard data processing and downlink technologies. We have previously proposed a new GPU accelerated onboard data processing architecture and developed parallelised image processing software to demonstrate the achievable data processing throughput and compression performance. However, the environmental characteristics are distinctly different to those on Earth, such as available power and the probability of adverse single event radiation effects. In this paper, we analyse new performance results for a low power embedded GPU platform, investigate the error resilience of our GPU image processing application and offer two new error resilient versions of the application. We utilise software based error injection testing to evaluate data corruption and functional interrupts. These results inform the new error resilient methods that also leverages GPU characteristics to minimise time and memory overheads. The key results show that our targeted redundancy techniques reduce the data corruption from a probability of up to 46% to now less than 2% for all test cases, with a typical execution time overhead of 130%.
Kruzelecky Roman, Murzionak Piotr, Lavoie Jonathan, Sinclair Ian, Schinn Gregory, Underwood Craig, Gao Yang, Bridges Christopher, Armellin Roberto, Luccafabris Andrea, Cloutis Edward, Leijtens Johan (2018) VMMO Lunar Volatile and Mineralogy Mapping Orbiter, International Conference on Environmental Systems Proceedings 2018
MPB Communications Inc.
Understanding the lunar near-surface distribution of relevant in-situ resources, such as ilmenite (FeTiO3), and volatiles, such as water/ice, is vital to future sustained manned bases. VMMO is a highly-capable, low-cost 12U Cubesat designed for operation in a lunar frozen orbit. It accomodates the LVMM Lunar Volatile and Mineralogy Mapper and the CLAIRE Compact LunAr Ionising Radiation Environment payloads. LVMM is a multi-wavelength Chemical Lidar using fiber lasers emitting at 532nm and 1560nm, with an optional 1064nm channel, for stand-off mapping of the lunar ice distribution using active laser illumination, with a focus on the permanently-shadowed craters in the lunar south pole. This combination of spectral channels can provide sensitive discrimination of water/ice in various regolith. The fiber-laser technology has heritage in the ongoing Fiber Sensor Demonstrator flying on ESA's Proba-2. LVMM can also be used in a low-power passive mode with an added 280nm UV channel to map the lunar mineralogy and ilmenite distribution during the lunar day using the reflected solar illumination. CLAIRE is designed to provide a highly miniaturized radiation environment and effect monitor. CLAIRE draws on heritage from the MuREM and RM payloads, flown on the UK?s TDS-1 spacecraft. The payload includes PIN-diode sensors to measure ionizing particle fluxes (protons and heavy-ions) and to record the resulting linear energy transfer (LET) energy-deposition spectra. It also includes solid-state RADFET dosimeters to measure accumulated ionizing dose, and dose-rate diode detectors, designed to respond to a Coronal Mass Ejection (CME) or Solar Particle Event (SPE). CLAIRE also includes an electronic component test board, capable of measuring SEEs and TID effects in a selected set of candidate electronics, allowing direct correlations between effects and the real measured environment.
This paper describes an agent platform based on the Foundation for Intelligent Physical Systems Abstract Architecture, which, together with a highly fault tolerant, bio-inspired hardware architecture, aims to increase the reliability of future, low-cost satellites. To achieve the stringent operational requirements imposed by the real-time and resource-constrained environment of a satellite, the Hybrid Agent Real-Time Platform (HARP) distinguishes itself from other platforms in three areas. Firstly, the HARP middleware uses discrete processors, instead of virtual machines or interpreters, as its agent execution environment. This has the advantage of reducing the agency memory footprint and enabling agents to perform real-time tasks. Secondly, the HARP communication stack makes use of ISO-TP over CAN 2.0A as its transfer level protocol, cutting out resource-intensive layers such as HTTP and IIOP. In addition, the communication stack allows real-time CAN traffic to share the network and be given priority over Agent Communication Language messages. Finally, the HARP middleware embeds a peer-to-peer task manager in each agency, allowing systems which are built using the bio-inspired Artificial Stem Cell Architecture and HARP middleware to autonomously reconfigure in the event of failures. The detailed design of the HARP middleware is given, together with details of an implementation of the HARP middleware on a set of prototype satellite hardware. The performance and scaling potential of the middleware, determined through a set of physical experiments, provide evidence of the practical feasibility of the proposed architecture.
Blott R, Baan WA, Boonstra AJ, Bergman J, Robinson D, Liddle D, Navarathinam N, Eves S, Bridges Christopher, Gao S, Bentum Marinus Jan, Forbes A, Humphreys D, Harroch CG (2013) Space-based ultra-long wavelength radio observatory (low cost) - SURO-LC, European Planetary Science Congress 2013 8 pp. 1-2
SURO-LC is the radio astronomer's equivalent of the first high resolution X-ray space telescopes. It opens up a largely unexplored spectral band, previously hidden from Earth, to make new discoveries in the nearby and distant universe. The proposed mission offers the first omnidirectional low frequency radio survey at high sensitivity and high resolution. SURO-LC all-sky or rapid monitoring (for rapid solar and galactic events) operation is in the largely un-explored frequency domain between 0.1 and 70 MHz, of which the 0.1 - 30 MHz range is mostly inaccessible from earth because of ionospheric blocking and man-made radio frequency interference (RFI). SURO-LC deploys a formation of nine spacecraft in a low relative-drift Lissajous orbit at SEL2, 1.5 million km from earth in a radio clean environment. Eight spherically distributed Cubesat daughters, equipped with 3 orthogonal dipole antennas, form a distributed interferometric radio telescope. An offset mothership provides data acquisition, digital signal processing, and ground communication.
Satellite conjunctions in space are highly challenging because of the lack of space situational awareness solutions and orbit data sharing schemes. Two Line Elements set (TLEs) are commonly used to define satellite state on orbit but are highly inaccurate. Similarly, Global Positioning System (GPS) used for positioning and tracking purposes is not, as a standalone solution, optimised for satellite traffic management. Therefore, an autonomous system specifically designed for space traffic management is needed. A new approach has been adapted for different satellite conjunction scenarios and investigated in a way that each satellite is equipped with a radio measurement instrument operating in multiple low-noise bands taking advantage of Software Defined Radio (SDR) concepts. Relative range between satellites has been obtained from the Received Signal Strength (RSS) by implementing adaptive changes in operating frequencies. Doppler frequency shifts have also been obtained which also have a significant importance on tracking satellites. Our results show that for a two-satellite scenario, it is possible to receive a signal with 20 dB signal to noise ratio from approximately 1800 km when operating at High Frequency (HF) and 600 km at Very High Frequency (VHF). Consequently, in a 600-satellite scenario, more than 79 satellites were detected by a main satellite observer when operating at 30 MHz whereas only 10 and 5 satellites were detected when operating at 140.8 MHz and 440.01 MHz respectively. Operating at the higher frequencies (2499 and 5088 MHz) yielded two dangerous close approaches with a maximum relative range of 2 km using both RSS and Doppler. Further, a second method of estimating range based on time of flight (ToF) has been implemented showing directly dependant ranging errors from signal processing and propagation time delays. Combining different ranging methods and altering between transmitting frequencies by using enabling SDR technologies helps to develop a new highly accurate collision detection system which can complement the existing systems and define the nature of satellite conjunctions in space.
AMSAT-UK and the Surrey Space Centre are cooperating in delivering an educational communication payload for the ESA European Student Earth Orbiter (ESEO) mission, comprising a payload computer, an L-band receiver and a VHF transmitter. The primary purpose of the payload is to provide downlink telemetry that can be easily received by schools and colleges for educational outreach purposes . Common space industry standards such as European Cooperation for Space Standardization (ECSS) consist of a large number of documents that were primarily written for large-scale space missions. Academic space projects cannot follow these design guidelines due to a lack of sufficient expertise, human resources, facilities or equipment. However, many projects were successfully developed, launched and operated with major deviations from ECSS standards. A recently published CubeSat standard consists of tailored ECSS requirements with the aim to improve the applicability of these specifications to small satellite projects. These, however, are still incompatible with the limited working environment of most university projects. In recent years, a `lean satellite' design approach that utilises non-traditional, risk-taking development and management was proposed by Cho et al.  to address these issues. This design approach was successfully applied by the AMSAT project team to develop a proto-flight model of the payload which entailed an improvement of customer specification compliance from 81% to 86% with respect to the engineering model. This method allowed a low cost and fast development process as well as passing all functional and environmental tests without major issues. A key finding was that despite having superior facilities, equipment and expertise compared to most academic CubeSat teams, only an overall compliance of 82% to the CubeSat standard and 57% to the analysed set of ECSS specifications could be achieved. This shows the challenge small space projects face when following conventional industry specifications such as ECSS which are written for traditional space missions. Following this, it is recommended to further promote the development of a new ISO standard for lean satellite design which could ease the development process and reliability of small space projects that struggle to fully comply to ECSS or CubeSat specifications.
Bergman JES, Bridges Christopher, Bruhn F, Gao Yang, Lappas V, Liddle D, Mouginis-Mark P, Nunes M, Palmer P, Sorensen T, Underwood Craig (2014) Characterizing the RF Quiescence of the Lunar Far Side Using a Constellation of Small Satellites, EPSC Abstracts; European Planetary Science Congress 2014 9
European Planetary Science Congress
Observations of highly red-shifted 21-cm hydrogen signals have been suggested as the only means to probe the early Universe from recombination to reionization. During this era, called the Dark Ages, the Universe consisted of neutral hydrogen gas and was opaque to light. It did not become transparent, as we see it today, until reionization was completed. The Dark Ages was the time period when matter clumped together, the very first stars and black holes were born, and, eventually, the first galaxies were formed. To enable observations of the Dark Ages is therefore one of the top priorities in cosmology and astrophysics. Today, the cosmological 21-cm signals are highly red-shifted and should peak in the FM radio band. Observing the Dark Ages from Earth is therefore next to impossible, due to man-made radio frequency interference (RFI) and ionospheric disturbances. To efficiently block the RFI, which would otherwise overwhelm the weak cosmological signal; it has been proposed to use the Moon as a radio shield and either place a satellite equipped with an ultra-sensitive radio instrument in lunar orbit or to deploy a large low-frequency radio array on the far-side of the Moon. Such missions are technically challenging and expensive and have so far failed to gain support from any national or international space program. Our goal is therefore to use a constellation of small inexpensive satellites in lunar orbit to collect pathfinder data, which would demonstrate EPSC Abstracts Vol. 9, EPSC2014-798, 2014 European Planetary Science Congress 2014 c Author(s) 2014 EPSC European Planetary Science Congress the feasibility of using the Moon as a radio shield, and map out the spatial extent of this RF quiescent zone to support future missions to explore the cosmos. This paper examines the design and radio payload of this mission. Alternative orbits, constellation and payload designs are analyzed to optimize the mission for performance and cost.
Taylor Benjamin, Underwood Craig, Viquerat Andrew, Fellowes Simon, Duke Richard, Stewart Brian, Aglietti Guglielmo, Bridges Christopher, Schenk M, Massimiani Chiara, Masutti D, Denis A (2018) Flight Results of the InflateSail Spacecraft and Future Applications of Drag Sails, 32nd Annual AIAA/USU Conference on Small Satellites pp. 1-12
AIAA/Utah State University
The InflateSail CubeSat, designed and built at the Surrey Space Centre (SSC) at the University of Surrey, UK, for the Von Karman Institute (VKI), Belgium, is one of the technology demonstrators for the QB50 programme. The 3.2 kilogram InflateSail is ?3U? in size and is equipped with a 1 metre long inflatable boom and a 10 square metre deployable drag sail.
InflateSail's primary goal is to demonstrate the effectiveness of using a drag sail in Low Earth Orbit (LEO) to dramatically increase the rate at which satellites lose altitude and re-enter the Earth's atmosphere. InflateSail was launched on Friday 23rd June 2017 into a 505km Sun-synchronous orbit. Shortly after the satellite was inserted into its orbit, the satellite booted up and automatically started its successful deployment sequence and quickly started its decent. The spacecraft exhibited varying dynamic modes, capturing in-situ attitude data throughout the mission lifetime. The InflateSail spacecraft re-entered 72 days after launch.
This paper describes the spacecraft and payload, and analyses the effect of payload deployment on its orbital trajectory. The boom/drag-sail technology developed by SSC will next be used on the RemoveDebris mission, which will demonstrate the applicability of the system to microsat deorbiting.
A new class of low-cost satellites has the potential to reduce the cost of traditional space-based services. Unfortunately, to date, low-cost satellites have proven to suffer from poor reliability. While traditional techniques for increasing reliability are well known to satellite developers, these techniques are poorly suited for implementation on low-cost satellites due to intrinsic budgetary, mass and volume constraints. This research proposes that alternative techniques for increasing system reliability can be derived by studying biological organisms, which have proven their robustness by inhabiting even the harshest locations on earth. Both unicellular and multicellular organisms are examined. The result is a conceptual system architecture, based on initially identical, reconfigurable hardware blocks, or artificial cells, and a decentralized task management strategy. This multicellular architecture is described in detail. Finally, preliminary details of a planned implementation are given. This implementation aims to demonstrate that a significant portion of traditional satellite avionics can be replaced by the proposed artificial cells.
Software Defined Radios (SDRs) have emerged as a viable approach for space communications over the last decade by delivering low-cost hardware and flexible software solutions. The flexibility introduced by the SDR concept not only allows the realization of multiple standards on one platform, but also promises to ease the implementation of one communication standard on differing SDR platforms by waveform porting. This technology would facilitate implementing reconfigurable nodes for parallel satellite reception in Mobile/Deployable Ground Segments. The SDR architecture was implemented initially in C/C++ and tested over varied embedded platforms and at different data rates from 1.2 to 19.2 kbps. Profiling using gprof demonstrated the need to move the up and down sampling blocks demanding higher computation to Field Programmable Gate Array (FPGA) logic in order to benefit new architecture optimization and thereby facilitating more than one signal at any given time. The paper includes the implementation of the Digital Down Converter (DDC) block in VHDL and design tradeoffs that yields insight into optimal solutions along with effective evaluation of the new candidate architecture.
Berthoud L, Glester A, Angling M, Baker A, Bannister N, Bowden K, Bowman P, Bridges Christopher, Forte B, Jones M, Burgon R, Kingston J, Macdonald M, McMillan A, Raper I, Whyndham M, Smith K, Toomer C (2018) Space Universities Network - Supporting space science and engineering higher education community in the UK, 2nd Symposium on Space Educational Activities Proceedings pp. 1-4
The world space economy is expected to grow to $400 billion by 2030 and to provide 100,000 jobs. In the UK we currently have 38,500 directly employed with a further 70000 jobs dependent on the space sector. By 2030 the UK aims to have a further 100,000 new people employed within the sector. Training space engineers and scientists is critical to fulfilling this need. The UK-based ?Space Universities Network? (SUN) was formed in 2016 with the aim of enhancing the quality of learning and teaching by providing support and resources to the Space science and engineering higher education community. SUN?s objectives are to facilitate the creation of a skilled workforce of graduates who can meet the challenges of future scientific and commercial exploitation of space. The network addresses this need by helping to inspire students to join the space sector and ensuring they are well equipped at University to contribute. SUN enables the developing, sharing and promotion of effective practice and innovation in the delivery of university-level space science and engineering curricula. It does this through workshops, offering opportunities for networking to support the space teaching community and a web-based repository of resources. This paper describes the process that led to the foundation of SUN, its objectives, modes of operation, prime activities, evaluation and future projects. Once firmly established, it is hoped to expand the network through partnerships with similar organisations in other countries.
Multicellular system architectures are proposed as a solution to the problem of low reliability currently seen amongst small, low cost satellites. In a multicellular architecture, a set of independent k-out-of-n systems mimic the cells of a biological organism. In order to be beneficial, a multicellular architecture must provide more reliability per unit of overhead than traditional forms of redundancy. The overheads include power consumption, volume and mass. This paper describes the derivation of an analytical model for predicting a multicellular system's lifetime. The performance of such architectures is compared against that of several common forms of redundancy and proven to be beneficial under certain circumstances. In addition, the problem of peripheral interfaces and cross-strapping is investigated using a purpose-developed, multicellular simulation environment. Finally, two case studies are presented based on a prototype cell implementation, which demonstrate the feasibility of the proposed architecture.
Non-cooperative tracking of shipping from space has traditionally been the preserve of state actors. Recent progress in nanosat and SDR technology raises the possibility of conducting such surveillance from low-cost space platforms. While ships may switch off beacons in order to obscure their location, they cannot proceed safely without their navigation radar systems being operational. Radar emissions may be recorded to achieve geolocation. As the radar antenna is mechanically rotated, a periodic power peak is observed by a fixed receiver. A receiver in LEO will record differing interception times according to its motion and that of the emitter platform. A least squares estimator is used to compare possible emitter locations with the collected data in order to arrive at the most probable geolocation. The highly constrained geometry of the system reduces the search to a 1-dimensional one which significantly reduces the processing power required for a fast answer. It is suggested that power reduction resulting from a new algorithm, coupled with advances in nanosat and SDR technology enables a low-cost demonstrator mission. Additionally, using only one satellite removes the requirement for high-speed data links, further reducing weight and power needs. Accuracies of better than 20km have been recorded in simulations.
A perrenial question of Cubesats is why they are not yet used as platforms for truly operational application missions. The STRaND-1 mission described in this paper is used to demonstrate the hurdles which must be overcome in order to create cost-effective CubeSat platforms that are ready for operational missions with satisfactory design lifetime, reliability and availability objectives. STRaND-1 is the UK?s first CubeSat, and will be launched on the 25th of February 2013 on a PSLV into a dawn-dusk sun-synchronous orbit. As with many CubeSats, the goals of the successful 3U mission were rapid training and technology demonstration. The novelty (other than the technical novelty of testing the robustness of mobile phone electronics in the LEO environment) was the volunteer nature of the team, and that the organisations involved had previous operational small satellite mission experience. This paper takes a holistic view of the mission, critically reviewing the mission lifecycle from the initial concept design through to integration and testing, LEOP and initial mission results in respect of these hurdles to operational applications. The UK's small satellite technology demonstration mission - TDS-1 - is presented for contrast. Now ready for flight in Q3 2013, TDS-1 is an example of how a collaborative small sat technology demonstration mission can be accomplished at low cost and inside a rapid schedule. TDS-1 incorporates a suite of eight separate sensor payloads plus a novel set of advanced avionics. The design, concept of operations and management of TDS-1 enabled the platform enough flexibility to accommodate the payloads to change in both number and in bus resources required throughout the programme lifecycle, while avoiding the pitfalls of over-designing the system. The review is conducted with an eye to how a CubeSat mission differs from the commercial, small satellite approach to spacecraft engineering. In particular, lessons learnt on CubeSat general system design philosophy, data bus topologies, and management philosophies are discussed and compared against the more traditional small sat approach, something on which the Surrey community can speak with authority. Conclusions are drawn on the the similarities and differences of the small-satellite approach pioneered in the 1990s and the CubeSat approach pioneered in the 2000s, with recommendations on where commercial, small satellite engineering philosophy can be applied to the hypothetical operational CubeSat mission, and vice versa.
Taylor Benjamin, Massimiani C, Duke Richard, Stewart Brian, Fellowes Simon, Bridges Christopher, Aglietti Guglielmo (2017) The AlSat-1N CubeSat Mission, AAS Advances in the Astronautical Sciences 163
This study establishes the optimal Single Event Upset (SEU) mitigation strategy for Xilinx's 7-Series Field Programmable Gate Arrays (FPGAs). This enables 7-Series FPGAs to be utilised in systems with high exposure to ionising radiation over Xilinx's smaller, radiation-hardened 4-Series and 5-Series FPGAs. The optimal strategy maximises system up-time, with minimal complexity and minimal risk of damaging the target FPGA device. Four SEU mitigation techniques are analysed and compared. Three of these are external scrubbing techniques; blind, readback, and blind with Frame Address Register (FAR) verification; with the fourth being Xilinx's internal scrubber, the Soft Error Mitigation (SEM) Intellectual Property (IP) core. The initial comparisons are quantitative, comparing the four methods for traits that lend themselves to meeting the criteria of the optimal scrubber. The techniques are then compared quantitatively to establish theoretical whole-device scan times for each technique given a range of errors to be corrected. These scan times can be utilised to determine which technique performs the fastest given the error rate and technique parameters. The calculations and resultant data can be computed for every device in the 7-series range. The findings suggest that the optimal solution is to opt not for a traditional mitigation strategy, but for a dynamic mitigation strategy. The fastest scrubber is the SEM IP Core, predominantly due to being internal to the FPGA, and as error rates increase, there becomes a crossover point whereby the blind scrubber with FAR verification comes into play to scrub at higher error rates in a deterministic way. Additionally, it finds that the configuration scrubber can operate at higher frequencies in comparison to NASAs recommendation of scrubbing at an order of magnitude higher than the expected SEU rate. These results provide the optimal scrubber for the 7-Series FPGA, and bring into question the recommendation of scrubbing at a higher order of magnitude than the expected error rate. Additionally, Xilinx's guidance for their FPGAs brings in an essential bit ratio which determines what proportion of the FPGAs is actually being utilised by the design, thereby decreasing the proportion of the errors that impact the design as opposed to empty areas of the FPGA, and hence increasing the speed at which scrubbing can take place with reference to NASAs recommendation.
The use of commercial of the shelf (COTS) processors is increasingly attractive for the space domain, especially with emerging high demand applications in Earth observation and communications. An order of magnitude improvement in on-board processing capability with less size, mass, and power is possible, however, COTS parts still lag in terms of reliability in the space environment. Costly protection techniques to ensure resilience to single event effects (SEEs) is required. Whilst current software reliability techniques are only capable of detecting errors, and performing partial recovery, our research offers a step change for both error detection and recovery without degradation in fault coverage. This targets modern multicore processors. We have previously shown how to create additional passes in the compiler's intermediate representation layer to automatically add differing protection codes at compile-time using the LLVM compiler framework. LLVM is supported by multiple processing architectures, and multiple high level languages - meaning it can be ported to not just space applications, but aerospace, defence, medical, and automotive. In this paper a new LLVM fault injection tool is presented to validate and measure software protection methods - either statically at compile time or dynamically at runtime for multiple errors such as silent data corruption (SDC), control/flow errors, and crashes. We use our tool to inject faults into unprotected and protected codes and make quantitative comparisons of the errors and associated statistical confidence. Our protection method shows high coverage, up to 100% for some benchmarks, and does not assume that the memory system is protected via typical TMR hardware approaches. This means that we protect all memory instructions that use read and write. Another reason for the high coverage is the inclusion of multiple data and instruction types (i32, i32*, i1, i8, i8*, i64, float & double, float & double pointers). This research has been implemented in two processing architectures; Intel core i5-3470 with 3.2 GHz frequency and a Raspberry Pi 3. On the 1 st processing platform the overhead was less than 15% and on the 2 nd platform the overhead was less than 17%.
Underwood Craig, Viquerat Andrew, Schenk Mark, Taylor Ben, Massimiani Chiara, Duke Richard, Stewart Brian, Fellowes Simon, Bridges Chris, Aglietti Guglielmo, Sanders Berry, Masutti Davide, Denis Amandine (2019) InflateSail De-Orbit Flight Demonstration Results and Follow-On Drag-Sail Applications, Acta Astronautica - Proceedings of the 69th International Astronautical Congress (IAC)
International Astronautical Federation (IAF)
The InflateSail (QB50-UK06) CubeSat, designed and built at the Surrey Space Centre (SSC) for the Von Karman
Institute (VKI), Belgium, was one of the technology demonstrators for the European Commission?s QB50
programme. The 3.2 kg 3U CubeSat was equipped with a 1 metre long inflatable mast and a 10m2
sail. InflateSail's primary mission was to demonstrate the effectiveness of using a drag sail in Low Earth Orbit (LEO)
to dramatically increase the rate at which satellites lose altitude and re-enter the Earth's atmosphere and it was one of
31 satellites that were launched simultaneously on the PSLV (polar satellite launch vehicle) C-38 from Sriharikota,
India on 23rd June 2017 into a 505km, 97.44o
Shortly after safe deployment in orbit, InflateSail automatically activated its payload. Firstly, it inflated its metrelong
metal-polymer laminate tubular mast, and then activated a stepper motor to extend four lightweight bi-stable
rigid composite (BRC) booms from the end of the mast, so as to draw out the 3.1m x 3.1m square, 12mm thick
polyethylene naphthalate (PEN) drag-sail. As intended, the satellite immediately began to lose altitude, causing it to
re-enter the atmosphere just 72 days later ? thus successfully demonstrating for the first time the de-orbiting of a
spacecraft using European inflatable and drag-sail technologies.
The InflateSail project was funded by two European Commission Framework Program Seven (FP7) projects:
DEPLOYTECH and QB50. DEPLOYTECH had eight European partners including DLR, Airbus France, RolaTube,
Cambridge University, and was assisted by NASA Marshall Space Flight Center. DEPLOYTECH?s objectives were
to advance the technological capabilities of three different space deployable technologies by qualifying their
concepts for space use. QB50 was a programme, led by VKI, for launching a network of 50 CubeSats built mainly by
university teams all over the world to perform first-class science in the largely unexplored lower thermosphere.
The boom/drag-sail technology developed by SSC will next be used on a third FP7 Project: RemoveDebris,
launched in 2018, which will demonstrate the capturing and de-orbiting of artificial space debris targets using a net
and harpoon system. This paper describes the results of the InflateSail mission, including the observed effects of
atmospheric density and solar activity on its trajectory and body dynamics. It also describes the application of the
technology to RemoveDebris and its potential as a commercial de-orbiting add-on package for future space missions.
Eckersley S., Saunders C., Gooding D., Sweeting M., Whiting C., Ferris M., Friend J., Forward L., Aglietti G., Nanjangud A., Blacker P., Underwood C., Bridges C., Bianco P. (2018) In-Orbit Assembly of Large Spacecraft Using Small Spacecraft and Innovative Technologies, Proceedings of the 69th International Astronautical Congress (IAC)
International Astronautical Federation (IAF)
The size of any single spacecraft is ultimately limited by the volume and mass constraints of currently available
launchers, even if elaborate deployment techniques are employed. Costs of a single large spacecraft may also be
unfeasible for some applications such as space telescopes, due to the increasing cost and complexity of very large
monolithic components such as polished mirrors.
The capability to assemble in-orbit will be required to address missions with large infrastructures or large
instruments/apertures for the purposes of increased resolution or sensitivity. This can be achieved by launching
multiple smaller spacecraft elements with innovative technologies to assemble (or self-assemble) once in space and
build a larger much fractionated spacecraft than the individual modules launched.
Up until now, in-orbit assembly has been restricted to the domain of very large and expensive missions such as space
stations. However, we are now entering into a new and exciting era of space exploitation, where new mission
applications/markets are on the horizon which will require the ability to assemble large spacecraft in orbit. These
missions will need to be commercially viable and use both innovative technologies and small/micro satellite
approaches, in order to be commercially successful, whilst still being safety compliant. This will enable
organisations such as SSTL, to compete in an area previously exclusive to large commercial players. However, inorbit
assembly brings its own challenges in terms of guidance, navigation and control, robotics, sensors, docking
mechanisms, system control, data handling, optical alignment and stability, lighting, as well as many other elements
including non-technical issues such as regulatory and safety constraints. Nevertheless, small satellites can also be
used to demonstrate and de-risk these technologies.
In line with these future mission trends and challenges, and to prepare for future commercial mission demands, SSTL
has recently been making strides towards developing its overall capability in ?in-orbit assembly in space? using
small satellites and low-cost commercial approaches. This includes studies and collaborations with Surrey Space
Centre (SSC) to investigate the three main potential approaches for in-orbit assembly, i.e. deployable structures,
robotic assembly and modular rendezvous and docking. Furthermore, SSTL is currently developing an innovative
small ~20kg nanosatellite (the ?Target?) as part of the ELSA-d mission which will include various rendezvous and
docking demonstrations. This paper provides an overview and latest results/status of all these exciting recent in-orbit
assembly related activities.
Underwood Craig, Pellegrino Sergio, Priyadarshan Hari, Simha Harsha, Bridges Chris, Goel Ashish, Talon Thibaud, Pedivellano Antonio, Wei Yuchen, Royer Fabien, Ferraro Serena, Sakovsky Maria, Marshall Michael, Jackson Kathryn, Sommer Charles, Vaidhyanathan Aravind, Nair Sooraj Vijayakumari Surendran, Baker John (2018) AAReST Autonomous Assembly Reconfigurable Space Telescope Flight Demonstrator, Proceedings of the 69th International Astronautical Congress (IAC)
International Astronautical Federation (IAF)
In recent years, there has been a desire to develop space-based optical telescopes with large primary apertures.
Current monolithic large telescopes, as exemplified by 6.5m aperture James Webb Space Telescope, are limited by
the diameter of the launch vehicle ? despite their ability to unfold and deploy mirror elements. One method to
overcome this obstacle is to autonomously assemble small independent spacecraft, each with their own mirror, while
in orbit. In doing so, a telescope with a large, segmented primary mirror can be constructed. Furthermore, if each of
these mirrors is manufactured to have an identical initial shape and then adjusted upon assembly, a substantial
reduction in manufacturing costs can be realized. In order to prove the feasibility of such a concept, a collaborative
effort between the California Institute of Technology, the University of Surrey, and the Indian Institute of Space
Science and Technology has been formed to produce and fly the "Autonomous Assembly of a Reconfigurable Space
Telescope" (AAReST) mission.
AAReST comprises two 3U Cubesat-like nanosatellites (?MirrorSats?) each carrying an electrically actuated
adaptive mirror, and each capable of autonomous un-docking and re-docking with a central ?9U? class nanosatellite
(?CoreSat?), which houses two fixed mirrors and a boom-deployed focal plane assembly (camera). All three
spacecraft will be launched as a single ~30kg microsatellite package. The central premise is that the satellite
components can manoeuvre and dock in different configurations and the mirrors can change shape and move to form
focused images on the camera focal plane. The autonomous manoeuvres and docking will be under the control of the
Surrey developed electro-magnetic docking system and near infra-red lidar/machine-vision based relative navigation
On orbit, the mission profile will firstly establish the imaging capability of the compound spacecraft before
undocking, and then autonomously re-docking a single MirrorSat. This will test the docking system, autonomous
navigation and system identification technology. If successful, the next stage will see the second MirrorSat
spacecraft undock and re-dock to the core spacecraft to form a wide linear formation which represents a large (but
sparse) aperture for high resolution imaging. Celestial targets will be imaged. Currently, the flight hardware is under
construction and launch is planned for ~2019-2020. This paper details the mission concept, technology involved and
its testing and progress on the production of the flight hardware.
SDRs have emerged as a viable approach for space communications over the last decade by delivering low-cost hardware and flexible software solutions. The flexibility introduced by the SDR concept not only allows the realisation of concurrent multiple standards on one platform, but also promises to ease the implementation of one communication standard on differing SDR platforms by signal porting. This technology would facilitate implementing reconfigurable nodes for parallel satellite reception in Mobile/Deployable Ground Segments and Distributed Satellite Systems (DSS) for amateur radio/university satellite operations.
This work outlines the recent advances in embedded technologies that can enable new communication architectures for concurrent multi-satellite or satellite-to-ground missions where multi-link challenges are associated. This research proposes a novel concept to run advanced parallelised SDR back-end technologies in a Commercial-Off-The-Shelf (COTS) embedded system that can support multi-signal processing for multi-satellite scenarios simultaneously. The initial SDR implementation could support only one receiver chain due to system saturation. However, the design was optimised to facilitate multiple signals within the limited resources available on an embedded system at any given time. This was achieved by providing a VHDL solution to the existing Python and C/C++ programming languages along with parallelisation so as to accelerate performance whilst maintaining the flexibility. The improvement in the performance was validated at every stage through profiling.
Various cases of concurrent multiple signals with different standards such as frequency (with Doppler effect) and symbol rates were simulated in order to validate the novel architecture proposed in this research. Also, the architecture allows the system to be reconfigurable by providing the opportunity to change the communication standards in soft real-time. The chosen COTS solution provides a generic software methodology for both ground and space applications that will remain unaltered despite new evolutions in hardware, and supports concurrent multi-standard, multi-channel and multi-rate telemetry signals.
Vast Satcom Antenna (VASANT) is an ongoing system and business case development study for a very large radio-frequency antenna (>>40m diameter) assembled and/or fabricated in space. Such an antenna would be enabling for radical new commercial satcom services to complement the coming broadband satcom constellations. The disruptive capabilities from such a high gain, high bandwidth antenna include potentially building penetration (at VHF) and support for very compact, omni-directional user terminals.
Satellite conjunctions in space are a major problem for operators and governments due to the lack of coherent space situational awareness solutions. The tracking accuracy for two-line elements (TLEs) averages in kilometres with similar error boundaries making it limited for critical satellite collision prediction. The common practice using GPS provides high accuracy from centimetres to metres. However, satellite state data (position and velocity) are often never shared and orbit determination methods provide limited solutions at quantifying near-miss events. In the advent of mega-constellations, there is an urgent need for in-situ measurements to develop real satellite traffic management solutions and associated satellite traffic data standardisation to complement and refine the existing techniques. This research presents ToF range estimation techniques adapted for the increasing low Earth orbit satellite traffic that requires co-operative monitoring. Two techniques are investigated namely, two-way time transfer (TWTT) and two-way ranging using direct sequence spread spectrum (TWR-DSSS). Although both techniques reached centimetre-level accuracies (7 to 15 cm) in perfect communications conditions, this accuracy drops quickly when considering the real-world limitations. TWTT technique is affected by processing delay and relative clock drifts. Consequently, the ranging errors standard deviation for TWTT is 210 and 2075 m respectively for the delays 1 and 10 ¼s. It is also found that the relative clock drifts used for both satellites cause bias ranging errors as the best achieved accuracy is 170 m even when the delays are nullified. On the other hand, TWR-DSSS shows a robust performance against low signal-to-noise (SNR) levels. For instance, relative range is resolved with sub-kilometre accuracy for -20 dB SNR. Ultimately, inter-satellite cooperative RF ranging based on time of flight can offer real opportunities of a new measurement instrument complementing the existing satellite conjunction assessment tools.
The European Student Earth Orbiter (ESEO) is a micro-satellite mission to Low Earth Orbit and is being developed, integrated, and tested by European university students as an ESA Education Office project. AMSAT-UK and Surrey Space Centre are contributing to the mission with a transceiver and transponder similar to that of FUNcube-1 with the addition of utilising an Atmel AT32 processor for packet software-redundancy, baseband processing, forward error correction, and packet forming; acting as a step towards software defined radio using automotive microprocessors . As on the FUNcube-1 satellite, the telemetry formats and encoding schemes presented utilize a large ground network of receivers on the VHF downlink and conforms to 1200 bps and a new 4800 bps redundant downlink for the rest of the spacecraft. The uplink is on L-band using bespoke partial-CCSDS frames.
This paper describes the lean satellite design approach introduced by Cho et al.  for hardware and software development and testing of the proto-flight model (PFM) payload computer. Furthermore, it assesses the compliance of the project to customer and ESA specifications and discusses the applicability of these standards. Finally, lessons learned are elaborated to provide guidance for future small satellite projects. Through multiple student projects, it was possible to successfully develop a proto-flight model using the lean satellite design approach which entailed an improvement of customer specification compliance from 81% to 86% comparing to the engineering model.
In software, utilising the Google Test Suite for verification of the SDR functions and FreeRTOS tools allowed students to optimize processor load margins to 30% when operating parallelized ADC and DAC, and CAN-open telemetry chains and exploring stable memory operations. A further finding was that in Summer 2017, there was an overall compliance of 82% to the CubeSat standard and 57% to the analysed set of ECSS specifications could be achieved. The poorer compliance in ECSS is due to the incomplete environmental testing at that time. The unfunded and student-based nature of the project places significant challenges when compared to conventional missions ? but this was outweighed by the ESEO flight opportunity. Following this, we recommended to further the development of a new ISO standard for lean satellite design as initiated by Cho et al.  which eases the development process and reliability of small space projects that struggle to fully comply to ECSS or CubeSat specifications. ESA have since defined a subset of ECSS Specifications for educational and CubeSat missions.
Interest is increasing in the use of neural networks
and deep-learning for on-board processing tasks in the space
industry . However development has lagged behind terrestrial
applications for several reasons: space qualified computers
have significantly less processing power than their terrestrial
equivalents, reliability requirements are more stringent than the
majority of applications deep-learning is being used for. The long
requirements, design and qualification cycles in much of the space
industry slows adoption of recent developments.
GPUs are the first hardware choice for implementing neural
networks on terrestrial computers, however no radiation
hardened equivalent parts are currently available. Field Programmable
Gate Array devices are capable of efficiently implementing
neural networks and radiation hardened parts are
available, however the process to deploy and validate an inference
network is non-trivial and robust tools that automate the process
are not available.
We present an open source tool chain that can automatically
deploy a trained inference network from the TensorFlow framework
directly to the LEON 3, and an industrial case study of
the design process used to train and optimise a deep-learning
model for this processor. This does not directly change the
three challenges described above however it greatly accelerates
prototyping and analysis of neural network solutions, allowing
these options to be more easily considered than is currently
Future improvements to the tools are identified along with a
summary of some of the obstacles to using neural networks and
potential solutions to these in the future.
Presented here is CHAFF (CubeSat Hyperspectral Application For Farming), a design concept for a CubeSat-based Hyperspectral Imager (CHSI) intended to supply high quality hyperspectral image data cubes to the agricultural community. CHAFF has been designed holistically as a system, considering all design and operational characteristics of a CHSI instrument and platform together: including the re-stricted payload mass and volume associated with CubeSats, the platform pointing stability/accuracy limitations, and the restricted downlink data budget. To this end, CHAFF will employ optically aided geometric co-registration methods, which will allow on-board construction of the hyperspectral data cube. This allows the use of powerful lossless data compression schemes to mitigate the downlink data budget limitations. In addition, a calibration methodology using a tuneable laser source at NPL, will be employed pre-flight to achieve rapid and accurate spectral and radiometric calibration, essential for the production of science-grade data sets from the proposed CubeSat constellations. A benchtop prototype has been constructed and a promising spectral resolution of 3nm at around 625nm has been achieved. In addition the auxiliary imager for the optically-aided geometric co-registration has been demonstrated.
The InflateSail (QB50-UK06) CubeSat, designed and built at the Surrey Space Centre (SSC) for the Von Karman Institute (VKI), Belgium, was a technology demonstrator built under the European Commission?s QB50 programme. The 3.2 kilogram 3U CubeSat was equipped with a 1 metre long inflatable mast and a 10m2 deployable drag sail and was one of 31 satellites that were launched simultaneously on the PSLV (polar satellite launch vehicle) C-38 from Sriharikota, India on 23rd June 2017 into a 505km, 97.44o Sun-synchronous orbit. Shortly after insertion into orbit, InflateSail automatically activated its drag-sail payload, and, as planned, began to lose altitude, causing it to re-enter the atmosphere just 72 days later ? successfully demonstrating for the first time the de-orbiting of a spacecraft using European inflatable and drag-sail technologies. This paper discusses the dynamics we observed during the descent, including the sensitivity of the craft to atmospheric density changes. The InflateSail project was funded by two European Commission Framework Program Seven (FP7) projects: DEPLOYTECH and QB50. QB50 was a programme, led by VKI, for launching a network of 50 CubeSats built mainly by university teams all over the world to perform first-class science in the largely unexplored lower thermosphere.
The dimensionality and volume of raw payload data generated onboard Earth Observation (EO) satellites has increased beyond the capabilities of satellite downlink technologies, as a result a bottleneck in the data delivery chain has developed. This data bottleneck must be alleviated in order for EO satellites to efficiently deliver the quality and quantity of payload data now expected by its reliant applications. In this thesis, hardware architectures, processing algorithms and software design are aspects explored towards a solution.
As a result, a new onboard satellite data processing architecture is proposed. The key novelties of the proposed system are the use of a Graphical Processing Unit (GPU), to facilitate state-of-the-art image processing, and the highly flexible nature of the architecture, enabling an adaptive processing chain that can be deployed across numerous platforms and missions. In addition, the research documented in this thesis aims to demonstrate the viability and evaluate the advantages of using low-power GPUs in an onboard data processing system.
Onboard suitable GPU optimised software development approaches are proposed and practically assessed by leveraging the state-of-the-art image compression algorithm, CCSDS-123, as a case study. Firstly, application development for maximised processing throughput is investigated using hyperspectral and multispectral EO data sets. The processing throughput, compression ratio and power consumption of the new CCSDS-123 image compression GPU application are assessed and characterised for a desktop GPU and the onboard representative low power NVIDIA Jetson TX1 GPU platform. Secondly, software based error injection experiments are leveraged to investigate the error resilience of the CCSDS-123 GPU application. This is a vital area of research which is required to facilitate the wider acceptance and use of GPU devices in space and safety critical applications, where errors are possible and cannot be tolerated. Using these results new error mitigation techniques are also proposed and evaluated.
Nanjangud Angadh, Underwood Craig I., Bridges Christopher P., Saaj Chakravarthini M., Eckersley Steve, Sweeting Martin, Biancod Paolo (2019) Towards Robotic On-Orbit Assembly of Large Space Telescopes: Mission Architectures, Concepts, and Analyses, Proceedings of the International Astronautical Congress, IAC pp. 1-25
International Astronautical Federation
Over the next two decades, unprecedented astronomy missions could be enabled by space telescopes larger than the
James Webb Space Telescope. Commercially, large aperture space-based imaging systems will enable a new generation
of Earth Observation missions for both science and surveillance programs. However, launching and operating
such large telescopes in the extreme space environment poses practical challenges. One of the key design challenges
is that very large mirrors (i.e. apertures larger than 3m) cannot be monolithically manufactured and, instead, a segmented
design must be utilized to achieve primary mirror sizes of up to 100m. Even if such large primary mirrors
could be made, it is impossible to stow them in the fairings of current and planned launch vehicles, e.g., SpaceX?s
Starship reportedly has a 9m fairing diameter. Though deployment of a segmented telescope via a folded-wing design
(as done with the James Webb Space Telescope) is one approach to overcoming this volumetric challenge, it is considered
unfeasible for large apertures such as the 25m telescope considered in this study. Parallel studies conducted
by NASA indicate that robotic on-orbit assembly (OOA) of these observatories offers the possibility, surprisingly,
of reduced cost and risk for smaller telescopes rather than deploying them from single launch vehicles but this is
not proven. Thus, OOA of large aperture astronomical and Earth Observation telescopes is of particular interest to
various space agencies and commercial entities. In a new partnership with Surrey Satellite Technology Limited and
Airbus Defence and Space, the Surrey Space Centre is developing the capability for autonomous robotic OOA of large
aperture segmented telescopes. This paper presents the concept of operation and mission analysis for OOA of a 25m
aperture telescope operating in the visible waveband of the electromagnetic spectrum; telescopes of this size will be
of much value as it would permit 1m spatial resolution of a location on Earth from geostationary orbit. Further, the
conceptual evaluation of robotically assembling 2m and 5m telescopes will be addressed; these missions are envisaged
as essential technology demonstration precursors to the 25m imaging system.
CubeSats are being increasingly specified for demanding Earth observation and astronomical applications where precise pointing, agility, and stability are critical requirements. Such precision is difficult to achieve in the case of CubeSats, mainly because of their small moment of inertia, means that even small disturbance torques, such as those due to a residual magnetic moment, have a significant effect on the attitude of spacecraft. In addition, hardware limitations make the task more challenging.
The effect of magnetic disturbances has shown itself by the problem of high tumbling rates observed on several CubeSat missions, post-flight analyses indicate that this is often due to un-modelled magnetic moments, mainly caused by the current flowing in the spacecraft, and the fact that CubeSats are often not designed with magnetic cleanliness in mind. However, by contrast, the other typical attitude disturbance sources for spacecraft (gravity gradient, aerodynamic, and solar radiation pressure torques) decrease significantly when the satellites become small.
We investigated in this research the source of the residual magnetic field in CubeSats and the effect of the resulting disturbance on the attitude of the spacecraft. It has been found that, although the disturbances may be minimised by good engineering practice, in terms of reducing the use of permeable materials and minimising current-loop areas, these disturbances can still be an issue when a high degree of stability is required. We, therefore, proposed a new technique using a network of magnetometers to characterise and then compensate the residual magnetic moment on the ground and in flight. A hardware prototype has been developed and successfully tested with the engineering model of the boom payload of Alsat-1N CubeSat, magnetic air coils, and permanent magnets in a Helmholtz coils arrangement by implementing a network of eight miniature 3-axis magnetometers. These are used to determine the strength, the centre, and the direction of the dipole of the magnetic source.
?Recently there has been an increasing demand for
more powerful processors for the next-generation space missions, such as communication and earth observation. The challenge is how to improve the reliability of the processor under the ?single event
effects? in orbit. We have previously proposed a new way of implementing any traditional software error detection and correction techniques at instruction level, capable of covering both the CPU and caches of ?commercial off the shelf? processors. In this paper, a novel way of evaluation of the software protection is presented,
based on a theoretical model and software injection experiments to predict the reliability of the whole processing architecture. The fault injection will evaluate the ability of the protection code to detect and recover errors in addition to the accuracy of the reliability models, by comparing the reliability of the theoretical predictions
to the reliability of the injection experiments. Automatic compiler error detection and recovery improves the reliability of the system
by reducing the error rate of ?single event upsets.? In some benchmarks, the error rate was reduced to less than 1%. This research has been tested in two machines; Intel core i5-3470 and a Raspberry
Pi 3. On the first processor, the overhead was less than 15%, and on the second one, the overhead was less than 17%. This research
can also be ported to multiple high level languages, with the ability
to cover multiple instructions and datatypes
The use of Commercial Off-The-Shelf (COTS) processors is increasingly attractive for the space domain, especially with emerging high demand applications in Earth observation and communications. An order of magnitude improvement in on-board processing capability with less size, mass, and power is possible, however, COTS parts still lag in terms of reliability in the space environment. Costly protection techniques to ensure resilience to Single Event Effects (SEEs) is required. Whilst current software reliability techniques are only capable of detecting errors, and performing partial recovery, our research offers a step change for both error detection and recovery without degradation in fault coverage. This targets modern multicore processors.
This research presents a novel software technique Automatic Compiler Error-Detection and Recovery (ACEDR) for software error detection and recovery. This technique is capable of covering both the CPU and Memory of COTS processing architectures, where the corruption of data (RAM and CPU registers) accessed by instructions can be corrected. ACEDR does not require additional hardware modifications in order to have the capability of error detection and recovery. ACEDR is based on LLVM compiler framework, where it adds redundant instructions to the original code at compile-time, and inserts check instructions (voter function call) to enable it to decide the right outcome out of the three redundant instructions at run-time. To achieve high coverage, both CPU instructions, like the arithmetic and logic operations, and memory instructions, responsible for Reading/Writing (R/W) from/to memory have been triplicated and protected. This work does not provide protection to jump/conditional jump instructions, also bit flips that would transform instructions into other instructions are not considered in this work. The LLVM modifications consist of modifying the optimization phase of the compilation process, by adding two passes, an analysis and a transformation one. Analysis pass will provide information about the code, consisting of instruction types and some statistics that can be utilised to analyse the confidence level later. The transformation pass adds the protection code, where it takes information provided by the analysis and uses it to add the appropriate protection where needed.
This research also proposes an adaptive protection for the multicore processors, motivated by the fact that traditional software protection techniques are mostly focused on error detection, and ignore the recovery part. Our research offers a step change not only with its ability to detect and recover errors, but also with the ability to reduce the overhead while keeping high error coverage. This research offers the ability for the running software mode to change in real time, and provide the proper error detection and recovery technique depending on the error rate on orbit. Novel error detection and protection techniques have been implemented to provide the operation mode with the necessary resilience. This includes Instructions-TMR (ITMR), Threads-TMR (TTMR) and the combination of both ITMR and TTMR. Reliability prediction models have been presented in this research, in order to estimate the reliability.
The reliability equations will model the whole processing architecture using multiple parameters related to the hardware architecture and the environment. In order to determine the reliability added using our software protection techniques, all of the benchmarks have been tested using software fault injection, where an LLVM fault injector has been developed.
The reliability model is starting from the basic model of Markov chain. The reliability predictions depends on many factors specific to the hardware architecture used, including », the error rate of the Single Event Upsets (SEU). » changes depending on the cross section of the component. Another factor is the access rate (depends on the hit/miss rate of the com
In this work, we propose a design space exploration workflow and tool for generating reconfigurable deep learning hardware models for FPGAs. The workflow is broken down into two main parts, Offline Design Exploration (ODE) and Online Design Reconfiguration (ODR). Offline Design Exploration is automated through a workflow methodology which makes it possible for a designer to provide a Convolutional Neural Network (CNN) architecture and the option of providing additional design constraints in terms of latency and space. These automatically generate multiple design spaces which trade-off latency for resource utilization by dedicating varying processing elements through loop reordering, unrolling and pipelining. The second part of the process introduces online reconfiguration to the design space. Online Reconfiguration means the ability to modify the design at runtime after upload, by selectively running it partially or fully according to an application?s immediate requirements, this provides the design with flexibility which, we believe, is highly beneficial for future autonomous on-board applications. We validate our work on the Xilinx Zynq-7100 board at 200 MHz and use custom trained networks architectures on three datasets for image classification, MNIST, SVHN and CIFAR-10. ODE generated designs achieved latency trade-offs of 95x for MNIST, 71x for CIFAR-10 and 18x for SVHN. Trade-offs in resource utilization in terms of DSP Slices were 44x for MNIST, 52x for SVHN and 24x for CIFAR-10. For the ODR, a 0.7% accuracy loss was traded-off with x13 speedup and a 25% reduction in power for MNIST, a 2% accuracy loss was traded-off with a 14x speedup and a 28% power reduction for SVHN, a 4% accuracy loss was traded off for a 50x speedup with 32.5% power reduction for CIFAR-10.