Space telescopes are our ‘eyes in the sky’ that enable unprecedented astronomy missions and also permit Earth observation integral to science and national security. On account of the increased spatial resolution, spectral coverage, and signal-to-noise ratio, there is a constant clamour for larger aperture telescopes by the science and surveillance communities. This paper addresses a 25 m modular telescope operating in the visible wavelengths of the electromagnetic spectrum; such a telescope located at geostationary Earth orbit would permit 1 m spatial resolution of a location on Earth. Specifically, it discusses the requirements and architectural options for a robotic assembly system, called Robotic Agent for Space Telescope Assembly (RASTA). Aspects of a first-order design and initial laboratory test-bed developments are also presented.
Vision based object detection is a key feature within planetary rover navigation which facilitates several functions such as hazard avoidance, localization and path planning. Most of the current research is based on stereoscopic vision or multiple cameras strategically placed along the rover chassis that perform one specific function. This works for large rovers with sufficient processing power, however such resources would not be very practical for small or micro-rovers. This thesis aims to extract terrain surface information from a single camera mounted on a micro-rover such as the Surrey Mobile Autonomy and Robotics Testbed (SMART) based on minimal computational resources. The terrain surface information can provide feature inputs to other on-board navigation functions such as the Planetary Monocular Simultaneous Localisation and Mapping (PM-SLAM) and constellation matching. The detected terrain surface can also be of scientific interest due of the geometrical characteristics produced from this research. This research aims to improve the processing speed of the Guidance Navigation and Control (GNC) system using low level 2D image processing techniques. The methods employed result in a faster "perception stage" of the GNC with lower processing power requirements, creating structural information, shape descriptors and cognitive segmentation/classification of the rover’s surrounding environment. Although the initial application of this research is for planetary rovers, the research outcome is envisaged to be relevant, and hence transferable, to other vehicle navigation problems used on land, air or under water.
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 “co-operative” two-spacecraft rendezvous and docking mission demonstrator using microsatellites (an active Chaser and a passive Target), however the GNC model is generic and can be utilized for other “non-co-operative” rendezvous and docking missions. This paper presents the latest results from the study, particularly the mission analysis, GNC simulation and modelling, sensors, and key mission and spacecraft systems aspects. The results so far show that such a GNC model and mission demonstrator is feasible, and in line with anticipated UK regulatory constraints that may apply to the mission.
Earth Observation via satellite has been successfully used for several decades in many applications. Monitoring climate change is the most challenging one, as it requires highly accurate data to enable detection of small changes in naturally variable signals over different spatial and temporal scales. A measure used in metrology to assess the quality of the data is measurement uncertainty. However, to date, many satellite products still do not have uncertainties, the accuracy requirements are not defined precisely and even calibrations are performed without associated measurement uncertainty budgets. Thus is it often impossible to put an unbiased quality mark to the data that, by default, requires the highest levels of accuracy. This poses the risks of using poor quality data as the input to climate change models.
This research focuses on the ____ground truth" measurement methodology called vicarious calibration. This is an independent post-launch satellite calibration technique based on a comparison of satellite readings with ground data and atmospheric modelling. Two test sites were selected as examples, land and ocean, to have uncertainty evaluated for their ground products following the Guide to the Expression of Uncertainty in Measurement (GUM) methodology.
A new radiometric calibration site, Gobabeb in the Namib Desert, was established for radiometric calibration of Top-of-Atmosphere (TOA) radiance/reflectance level 1 (L1) satellite products, and a campaign was conducted to measure the ground's reflectance. All instruments used during the initial characterisation were previously calibrated and characterised in optical laboratories. The in situ uncertainty budget was evaluated and validated by the comparison of the results to an alternative measurement source. The primary input of this research to the scientific community, apart from the new site, is a revised SI traceability chain for the ground reflectance field measurements. Hitherto, the reflectance reference standards used in situ had a calibration that did not match field illumination conditions. Although this problem was known, often it was not addressed or dealt with accurately. This study proposed a new field calibration value for the reflectance standard that combines direct and diffuse components weighted accordingly to the wavelength and atmospheric conditions during the measurement.
The work on the ocean site concentrated on the existing Boueé pour l’acquisition de Séries Optiques á Long Terme (BOUSSOLE) site that is permanently deployed in the Ligurian Sea and provides Bottom of Atmosphere (BOA) water leaving radiance/reflectance level 2 (L2) Ocean Colour System Vicarious Calibration (SVC). This site had a preliminary uncertainty estimated as one generic number for all spectral channels and environmental conditions. A new uncertainty budget was developed by a detailed evaluation of each identified uncertainty component and these were combined by applying the Monte Carlo Method (MCM). As a result, a dynamic uncertainty evaluation for each measurement and the spectral band was produced addressing real measurement conditions and their effects on the quality of the relevant in situ products.
Earth Observation (EO) via remote sensing is rapidly growing in terms of satellite missions, complexity of applications and number of datasets. This situation demands that data has associated with it a quality indicator that describes the compatibility between different sensor data and suitability for particular applications. This work describes a full end-to-end analysis of the uncertainty at a pixel level of the Top-Of-Atmosphere (TOA) radiance/reflectance factor products. It develops a methodology framework that can be adapted and reproduced by several EO missions to provide TOA radiometric uncertainty. The method is not only described but implemented as a software tool named Radiometric Uncertainty Tool (RUT) using as an example the Sentinel-2 (S2) mission. The uncertainty methodology starts from a radiometric model, where a set of uncertainty contributors are identified and specified at a pixel level, by reviewing the pre- and post-launch sensor radiometric characterisations. These contributors are assessed using the metadata and quality information associated to the satellite products where possible. As a consequence, the uncertainty contributions are specified for the specific satellite acquisition time, scene and processing. Some of the uncertainty contributions required the use of novel estimation methods that have been specifically applied to the assessment of the uncertainty propagation produced by the image orthorectification and the radiometric impact of the spectral knowledge. The study proposes an uncertainty combination model with an important effort in using the best metrological practices as described in the ‘Guide to Expression of Uncertainty in Measurement’ (GUM) model. The assumptions in the model have been validated by comparing the results to a Monte Carlo Method (MCM), the correlation among the different uncertainty contributions has been studied, and the impact of simplifications in the combination model has been assessed. As an extension of the work towards its larger application, a methodology has been proposed and implemented to estimate the uncertainty associated to the mean of the pixels in a Region of Interest (ROI). The study considers the correlation of the pixels in the spatial, temporal and spectral dimension. As a result, the TOA radiometric uncertainty estimates can be of direct use for applications as the radiometric validation activities or product spatial binning. Further extension of the uncertainty concepts has resulted in a set of tools, algorithms and methodologies that have been used in order to estimate the radiometric uncertainty achievable for an indicative target sensor through in-flight cross-calibration using a well-calibrated hyperspectral SI-traceable reference sensor with observational characteristics such as TRUTHS (Traceable Radiometry Underpinning Terrestrial and Helio-Studies) mission. This study considers the criticality of the instrumental and observational characteristics on pixel level reflectance factors, within a defined spatial ROI within the target site. It quantifies the main uncertainty contributors in the spectral, spatial, and temporal dimension.
Alex da Silva Curiel, Phil Whittaker, Rachel Bird, Andrew Haslehurst, Pejman Nejadi, Irwin Victoria, Andrew Cawthorne, Craig Underwood, Martin Sweeting (2019)Synthetic Aperture Radar on a Nanosatellite - is it Possible?, In: Proceedings of the 12th IAA Symposium on Small Satellites for Earth Observation
International Academy of Astronautics (IAA)
The implementation of a viable Synthetic Aperture Radar (SAR) mission using small satellites faces significant technological and financial challenges, and this paper evaluates how small such a spacecraft could be made whilst still fulfilling a useful mission. SAR offers a range of complementary capabilities alongside other Earth Observation systems with various unique features, but developing such spacecraft has traditionally been expensive and technologically challenging. It is only in the most recent years that small satellite SAR missions have been implemented and operated, and this paper examines the state of the art and the challenges. Furthermore the opportunities of how small SAR satellites can help realise new Earth Observation capabilities not available on existing traditional SAR satellites are described using examples of missions under development or reference design missions.
S Gao, K Clark, M Unwin, J Zackrisson, WA Shiroma, JM Akagi, K Maynard, P Garner, L Boccia, G Amendola, G Massa, C Underwood, M Brenchley, M Pointer, MN Sweeting (2009)Antennas for Modern Small Satellites, In: IEEE ANTENN PROPAG M51(4)pp. 40-56
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Modern small satellites (MSS) are revolutionizing the space industry. They can drastically reduce the mission cost, and can make access to space more affordable. The relationship between a modern small satellite and a "conventional" large satellite is similar to that between a modern compact laptop and a "conventional" work-station computer. This paper gives an overview of antenna technologies for applications in modern small satellites. First, an introduction to modern small satellites and their structures is presented. This is followed by a description of technical challenges in the antenna designs for modern small satellites, and the interactions between the antenna and modern small satellites. Specific antennas developed for modern small-satellite applications are then explained and discussed. The future development and a conclusion are presented.
Angadh Nanjangud, Craig I. Underwood, Christopher P. Bridges, Chakravarthini M. Saaj, Steve Eckersley, Martin Sweeting, Paolo Biancod (2019)Towards Robotic On-Orbit Assembly of Large Space Telescopes: Mission Architectures, Concepts, and Analyses, In: Proceedings of the International Astronautical Congress, IACpp. 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.
S. Eckersley, C. Saunders, D. Gooding, M. Sweeting, C. Whiting, M. Ferris, J. Friend, L. Forward, G. Aglietti, A. Nanjangud, P. Blacker, C. Underwood, C. Bridges, P. Bianco (2018)In-Orbit Assembly of Large Spacecraft Using Small Spacecraft and Innovative Technologies, In: 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.
Paul Cannon, Matthew Angling, Les Barclay, Charles Curry, Clive Dyer, Robert Edwards, Graham Greene, Michael Hapgood, Richard Horne, David Jackson, Cathryn Mitchell, John Owen, Andrew Richards, Christopher Rogers, Keith Ryden, Simon Saunders, Martin Sweeting, Rick Tanner, Alan Thomson, Craig Underwood (2013)Extreme space weather: impacts on engineered systems and infrastructure
Royal Academy of Engineering
Paul Stephens, John Cooksley, Alex da Silva Curiel, Lee Boland, Susan Jason, James Northam, Andrew Brewer, Javad Anzalchi, Hugh Newell, Craig Underwood, Stephen Machin, Wei Sun, Martin Sweeting (2003)Launch of the International Disaster Monitoring Constellation; the Development of a Novel International Partnership in Spacepp. 525-535
Three spacecraft for the UK, Turkey and Nigeria were launched together in September 2003, to join Algeria's satellite, AlSat-1, in the Disaster Monitoring Constellation (DMC). Surrey Satellite Technology Ltd. has designed, built and launched the world's first constellation to provide daily global Earth observation coverage at moderate resolution in three spectral bands. This international initiative will provide daily images for global disaster monitoring, as well as supporting each partner nation's indigenous remote sensing requirements. The DMC programme establishes a novel model for international collaboration, and demonstrates how small satellite missions can be employed for a wide range of applications. This paper shows the first in-orbit mission results from DMC satellites including examples of unique EO data products comprising up to 600 x 600 km images gathered at 32-metres GSD in 3 spectral bands.
A control system is proposed for a low Earth orbit gravity gradient stabilised microsatellite using Z wheel. The microsatellite is 3-axis stabilized using a yaw reaction wheel, with dual redundant 3-axis magnetorquers. Two vector magnetometers and four dual sun sensors are carried in order to determine the full attitude. The attitude was estimated using an Euler angles (small libration version) on based extended Kalman filter (EKF). After the satellite has been detumbled and deploy the gravity gradient boom, in order to have the accurate Nadir pointing we will use the Z zero-bias mode controller. The Z momentum wheel will be damped by the magnetorquers. This paper describes the attitude determination and control system design of LEO microsatellite using Z reaction wheel for yaw phase mode control and Z disturbance cancellation during X thruster firings for orbit maneuvers.
Stress in vegetation causes a small shift of the point of maximum slope in the spectral reflectance between 680nm and 750nm ?the so-called "red-edge" position (REP). This shift has been used as an indication of stress, both in the laboratory and in field measurements. The shift of the REP can be between 3 and 7 nm and is directly related to variations in the chlorophyll content and health condition of the plant and its leaves. The fundamental theory for this research has been the evaluation of the "red-edge" effect as a suitable means for detecting and monitoring vegetation stress using a small-satellite-borne remote sensing instrument as a cost-effective solution to global plant stress monitoring. In this work the design of a low cost instrument that uses the REP is proposed. The paper describes the fundamental theory that supports the design, and explains the main aspects of the proposed low-cost, compact hyperspectral instrument. The instrument is compatible with a small satellite platform and is proposed as a cost-effective solution for vegetation stress monitoring. Towards the instrument design, a radiometric analysis combined with the estimation of the red-edge position under different scenarios have proven to be very useful in the design of a hyperspectral solution for monitoring stress in vegetation. The existing solutions have been proved to be useful, but still have some limitations: the airborne sensors mainly in availability, coverage and cost. Space-borne instruments still need some improvements for this particular application, mainly in the spectral resolution to have sufficient spectral detail to be able to detect stress with greater accuracy.
EyasSAT is a revolutionary concept in space systems engineering education. Up until now, space systems engineering has been typically conducted behind the cloak of clean rooms protecting intellectual property by a select few individuals with millions of dollars at stake. To the contrary, EyasSAT has ushered in an opportunity for large numbers of students with varied backgrounds to build, test, and "fly" a satellite in the classroom, at virtually no financial risk. Student teams working in the context of an introductory, engineering, or professional short course are guided through virtually the entire satellite acquisition process. By the end of the course, students have worked through all the significant issues associated with each spacecraft subsystem and have a better understanding how they work in concert as a complete spacecraft system. A background on the EyasSAT development and system description is presented first. The focus of the paper is to report on the integration of EyasSAT into the University of Surrey's key space systems engineering courses: Space Mission Design for second year students and Spacecraft Bus Subsystems for third year students. The use of EyasSAT in other courses and to support student projects will also be discussed, including the first-ever student-built experiment module.
A Rachedi, K Belkacemi, AB Benbouzid, K Laidi, A Belghoraf, MN Sweeting (2009)Radiometric pre-Calibration of Alsat-1 Camera, In: RAST 2009: PROCEEDINGS OF THE 4TH INTERNATIONAL CONFERENCE ON RECENT ADVANCES IN SPACE TECHNOLOGIESpp. 361-366
In many types of space mission there is a constant desire for larger and larger instrument apertures, primarily for the purposes of increased resolution or sensitivity. In the Radio Frequency domain, this is currently addressed by antennas that unfold or deploy on-orbit. However, in the optical and infrared domains, this is a significantly more challenging problem, and has up to now either been addressed by simply having large monolithic mirrors (which are fundamentally limited by the volume and mass lifting capacity of any launch vehicle) or by complex ‘semi-folding’ designs such as the James Webb Space Telescope. An alternative is to consider a fractionated instrument which is launched as a collection of individual smaller elements which are then assembled (or self-assemble) once in space, to form a much larger overall instrument. SSTL has been performing early concept assessment work on such systems for high resolution science observations from high orbits (potentially also for persistent surveillance of Earth). A point design of a 25 m sparse aperture (annular ring) telescope is presented. Key characteristics of 1) multiple small elements launched separately and 2) on-orbit assembly to form a larger instrument are included in the architecture. However, on-orbit assembly brings its own challenges in terms of guidance navigation and control, robotics, docking mechanisms, system control and data handling, optical alignment and stability, and many other elements. The number and type of launchers used, and the technologies and systems used heavily affect the outcome and general cost of the telescope. The paper describes one of the fractionated architecture concepts currently being studied by SSTL, including the key technologies and operational concepts that may be possible in the future.
Astrophysicists demand larger (mirror diameter > 10m) space optical telescopes to investigate more distant events that happened during the very early period of the universe, for example formations of the earliest stars. The deployable telescope design like James Webb Space Telescope that has a 6.5m diameter primary mirror has already reached the capacity limits of the existing launch vehicles. Therefore, the space industry has been considering using robotic technologies to build future optical reflecting three-mirror structured space telescopes in orbit from smaller components.
One of the design paradigms is to use a high-DOF manipulator on a free-flying platform to build the optical telescope in orbit. This approach requires high precision and accuracy in the robotic manipulation GNC system that has several challenges yet to be addressed: 1. Orbital environmental parameters that affect sensing and perception; 2. Limitations in robotic hardware, trajectory planning algorithms and controllers.
To investigate these problems for in-orbit manipulation, the UK national hub on future AI and robotics for space (FAIR-SPACE) at the Surrey Space Centre (SSC) has been developing a ground-based hardware-in-the-loop (HIL) robotic demonstrator to simulate in-orbit manipulation. The key elements of the demonstrator are two 6-DOF manipulators and a re-configurable sensor system. One of the manipulators with a > 3-DOF gripping mechanism represents the assembly manipulator on a spacecraft whose orbital dynamics, kinematics, and environmental disturbances and uncertainties are propagated in a computer. The other 6-DOF manipulator with a torque/force sensor is used as a gravity offoad mechanism to carry the space telescope mirror segment. The relative motions between the service/manipulation arm and the mirror segment are computed and then executed by the second arm. The sensor system provides visual feedback of the end-effector and uses computer vision and AI to estimate the pose and position of the mirror segment respectively. The demonstrator aims to verify and validate the manipulator assembly approach for future large space optical telescopes against ground truth and benchmarks.
This paper explains the motivation behind developing this testbed and introduces the current hardware setup of the testbed and its key features.
A cold gas propulsion system is used for orbital maintenance on board microsatellite. Cold gas thrusters are the simplest way of achieving thrust. A microsatellite could be a part of the constellation and to maintain a daily coverage, it will be equipped with a propulsion system for an orbit control. A constellation of several microsatellites could be launched and put at the allocate position in the orbit. To do this, the satellites need few months to be in their final position. A propulsion system is used, among other things, to maintain the satellite at its nominal position. The wheels (reaction/momentum) will be used to dump the thruster disturbances caused by misalignment. This study describes the wheel attitude damping thruster disturbances of Low Earth Orbit (LEO) microsatellite for orbit maintenance with the following points: 1) Attitude dynamics, 2) External disturbances, 3) Magnetic wheel control, 4) Simulation results will be presented to evaluate the performance and design objectives. © 2006 Asian Network for Scientific Information.
– Proceedings of SPIE Defense, Security and Sensing Conference vol. 7347 “Evolutionary and Bio-Inspired Computation: Theory and Applications III”,
Y Gao, A Phipps, M Taylor, IA Crawford, AJ Ball, L Wilson, D Parker, M Sweeting, ADS Curiel, P Davies, A Baker, WT Pike, A Smith, R Gowen (2008)Lunar science with affordable small spacecraft technologies: MoonLITE and Moonraker, In: PLANETARY AND SPACE SCIENCE56(3-4)pp. 368-377
PERGAMON-ELSEVIER SCIENCE LTD
Image compression is an important requirement of imaging payloads on board Earth Observation satellites. This paper presents a new on-board real-time compression system, capable of lossless and lossy image compression. A cost-effective lossless image compression scheme, based on the CCSDS recommendation, is proposed and tested with multi/hyperspectral images. An efficient hardware implementation is achieved using FPGA-based acceleration. The hardware accelerator design is optimized by employing novel techniques at algorithmic and logic levels.
On board image data compression is an important feature of satellite remote sensing payloads. Reconfigurable Intellectual Property (IP) cores can enable change of functionality or modifications. A new and efficient lossless image compression scheme for space applications is proposed. In this paper, we present a lossless image compression IP core designed using AccelDSP, which gives users high level of flexibility. One typical configuration is implemented and tested on an FPGA prototyping board. Finally, it is integrated successfully into a System-on-Chip platform for payload data processing and control.
35. D.J. Barnhart, T. Vladimirova, A.M. Baker and M.N. Sweeting. - Proceedings of
DJ Barnhart, T Vladimirova, MN Sweeting, RL Balthazor, LC Enloe, LH Krause, TJ Lawrence, MG Mcharg, JC Lyke, JJ White, AM Baker (2007)Enabling Space Sensor Networks with PCBSatSSC07-
26. D. J. Barnhart, T. Vladimirova, M.N. Sweeting, R.L. Balthazor, L.C. Enloe, L.H. Krause, T.J. Lawrence, M.G. Mcharg, J.C. Lyke, J.J. White, A.M. Baker, Enabling Space Sensor Networks with PCBSat – Proceedings of the 21st Annual Conference on Small Satellites, ref. SSC07-IV-4, August 13-16, 2007, Utah State University, Logan Utah, USA.
The use of the Karhunen-Loève Transform (KLT) for spectral decorrelation in compression of hyperspectral satellite images results in improved performance. However, the KLT algorithm consists of sequential processes, which are computationally intensive, such as the Covariance and Eigenvector evaluations, etc. These processes slow down the overall computation of the KLT transform significantly. The acceleration of these processes within the context of limited power and hardware budgets is the main objective of this paper. The computations of each of these processes are investigated thoroughly by breaking them down into primitive arithmetic operations. Subsequently, a comprehensive analysis of these computations is presented to inspect the possibility and feasibility of different acceleration techniques, such as parallelism. The proposed designs are implemented on a System-on-a-Chip platform, which incorporates a 32-bit hardwired microcontroller and a coprocessing unit built within a field programmable gate array fabric. Two novel architectures are proposed offering accelerated processing within a very limited power budget (less than 0.225 Watt). The proposed solution is not only feasible for space applications, but also for different mobile and remote sensing applications. © 2012 IEEE.
Over the last decade, UK-based small satellite manufacturer Surrey Satellite Technology Ltd (SSTL) has developed and launched 6 Medium Resolution Imagers (MRI) on the SSTL-100 platform as part of the Disaster Monitoring Constellation (DMC). Currently, 5 DMC platforms are in operation augmented by platforms providing both high resolution and the MRI, such as the recently launched NigeriaSat 2 high resolution imager. The DMC constellation is operated by the consortium partners and co-ordinated by SSTL's subsidiary company DMC International Imaging Ltd (DMCii). There has been an interest in developing the DMC concept further to address a growing demand for additional capacity and capability. Consequently, two new developments of the MRI are planned for the future to enhance both the platform and the payload and provide the users with better coverage and a wider range of possible applications. The first enhancement has been enabled by platform improvements, particularly in the areas of power generation, data storage and communications. The enhancements allow the MRI to be operated whenever the satellite is flying over land and is called "Earthmapper". Earthmapper, offers full coverage of the Earth's land area in 5 days and opens up the possibility of a constellation of 5 Earthmappers imaging the whole world landmass every day. The second enhancement is a radically new optical design providing similar ground sampling to the current MRI on the SSTL-100 platforms but with significantly increased spectral range. This is an enhanced true colour imager incorporating several channels ranging from the blue to the SWIR that can, in principle, be tuned to the specific customer requirements. These two new developments are discussed below.
This paper describes a new high performance Earth Observation Platform, the SSTL-300, which has been developed to provide customers with a capability that has previously only been available at much higher cost and on larger platforms. This platform offers a 7-year mission lifetime with a very high operational availability. The main payload is a very high-resolution imager (VHRI) with a panchromatic 2.5m ground sampling distance (GSD) channel and four multi-spectral channels offering 5m GSD. The imager swath is 20km in all channels. This imager is an extension of the 4m GSD imager already flying on Beijing-1, which was launched in October 2005. Additional payloads can be accommodated, such as the Medium Resolution Imager (MRI), offering lower resolution of 22m or 32m GSD in four multiple spectral bands with 300km swath width. The 32m MRI has already flown on four previous Disaster Monitoring Constellation (DMC) Missions. High performance geo-location is provided, the performance of which is dependent on the chosen subsystem options. Simultaneous imaging is possible with the VHRI and the MRI and scenes can be as long as 2000km. The image data is compressed on-board, using lossless data compression, for store-and-forward operations. Furthermore, switchable encryption is available, using the Data Encryption Standard (DES), on the TM/TC as well as switchable scrambling on payload data. Near real-time imaging & down-linking is possible for a range of targets close to the ground station. A range of imaging modes are available including: strip mapping, fast response scene capture, stereo imaging, with pitch angles between 10 and 45 degrees to provide digital elevation models, and increased area coverage to provide wide-swath high-resolution imagery of up to 85km. The nominal orbit for the SSTL-300 will be sun-synchronous, with a 10.30am node to provide repeatable global coverage and good lighting conditions. The platform will orbit at approximately 700km, which provides good optimisation for single satellite and constellation revisits. On-board propulsion is included for orbit maintenance.
A new dimension of wireless sensor network architecture design is emerging where hundreds to thousands of ultra-light low-cost sensor nodes are required to collectively perform a spectrum of distributed remote sensing missions in hostile conditions, predominantly those encountered in space. Research is underway to investigate the feasibility of fabricating survivable self-powered sensor nodes monolithically with commercially available SiGe BiCMOS technology. This paper presents simulation and test chip results of two novel and essential building blocks: a photovoltaic/solar cell power supply and an environmentally tolerant microprocessor, based on radiation hardening by design and asynchronous logic.
A new class of remote sensing and scientific distributed space missions is emerging that requires hundreds to thousands of satellites for simultaneous multipoint sensing. These missions, stymied by the lack of a low-cost mass-producible sensor node, can become reality by merging the concepts of distributed satellite systems and terrestrial wireless sensor networks. A novel, subkilogram, very-small-satellite design can potentially enable these missions. Existing technologies are first investigated, such as standardized picosatellites and microengineered aerospace systems. Two new alternatives are then presented that focus on a low-cost approach by leveraging existing commercial mass-production capabilities: a satellite on a chip (SpaceChip) and a satellite on a printed circuit board. Preliminary results indicate that SpaceChip and a satellite on a printed circuit board offer an order of magnitude of cost savings over existing approaches.
A wide range of emerging applications is driving the development of wireless sensor node technology towards a monolithic system-on-a-chip implementation. Of particular interest are hostile environment scenarios where radiation an thermal extremes exist. Radiation hardening by design has been recognized for over a decade as an alternative open-source circuit design approach to mitigate a spectrum of radiation effects, but has significant power and area penalties. Similarly, asynchronous logic design offers potential power savings and performance improvements, with a tradeoff in design complexity and a lesser area penalty. These side effects have prevented wider acceptance of both design approaches. A case study supporting the development of monolithic system-on-a-chip wireless sensor nodes is presented. Synchronous, hardened, and asynchronous/hardened implementations of a textbook microprocessor in 0.35 mu m austriamicrosystems SiGe BiCMOS technology are compared. The synergy of this novel asynchronous/hardened design approach is confirmed by simulation and hardware results.
Modern computers are now far in advance of satellite systems and leveraging of these technologies for space applications could lead to cheaper and more capable spacecraft. Together with NASA AMES’s PhoneSat, the STRaND-1 nanosatellite team has been developing and designing new ways to include smart-phone technologies to the popular CubeSat platform whilst mitigating numerous risks. Surrey Space Centre (SSC) and Surrey Satellite Technology Ltd. (SSTL) have led in qualifying state-of-the-art COTS technologies and capabilities - contributing to numerous low cost satellite missions. The focus of this paper is to answer if 1) modern smart-phone software is compatible for fast and low cost development as required by CubeSats, and 2) if the components utilised are robust to the space environment. The STRaND-1 smart-phone payload software explored in this paper is united using various open-source Linux tools and generic interfaces found in terrestrial systems. A major result from our developments is that many existing software and hardware processes are more than sufficient to provide autonomous and operational payload object-to-object and filebased management solutions. The paper will provide methodologies on the software chains and tools used for the STRaND-1 smartphone computing platform, the hardware built with space qualification results (thermal, thermal vacuum, and TID radiation), and how they can be implemented in future missions.
D Barnhart, Martin Sweeting (2014)Right-sizing Small Satellites, In: Proceedings of the 28th Annual AIAA/USU Conference on Small Satellites, 2014
Spacecraft standardization has been a topic of great debate within the space community. This paper intends to be a provocative thought piece asking one fundamental question: “is there a ‘right size’ for small satellites?” In order to answer this question, we propose three top-down design factors for the space systems engineering process: spacecraft utility, mission utility, and optimum cost. Spacecraft utility quantitatively measures the capability of a spacecraft, derived from its volume and power properties. Mission utility then measures the aggregate value of a constellation. Optimum cost, which is a function of spacecraft mass and quantity, can be determined by assessing the break-even point. Data from the small satellite community, including USAF Academy FalconSAT and Surrey Satellite Technology Ltd. (SSTL) missions, is presented in support of this discussion, constrained to systems with a mass less than 200 kg. These design factors inform the mission developer in determining the appropriate system architecture. Using these design factors, a notional standardized spacecraft configuration is presented, with a mass of 30 kg and 50 cm cubed volume that optimizes spacecraft utility, mission utility, and cost.
S Gao, M Brenchley, M Unwin, CI Underwood, K Clark, K Maynard, L Boland, MN Sweeting (2008)Antennas for small satellites, In: Loughborough Antennas and Propagation Conferencepp. 66-69
Small low-cost satellites, pioneered at Surrey, are revolutionizing space. This paper gives an overview of antenna technologies for applications in small satellites. First, an introduction to small satellites and their structure is presented. This is followed by a description of the technical challenges of antenna design for small satellites. Various antennas for small satellite applications are illustrated. A conclusion and future work at Surrey Space Centre (SSC) and Surrey Satellite Technology (SSTL) is presented in the end.
In this paper, a full methodology to deal with microvibration predictions onboard satellites is described. Two important aspects are tackled: 1) the characterization of the sources with a pragmatic procedure that allows integrating into the algorithm the full effect of the sources, including their dynamic coupling with the satellite structure; 2) the modeling of the transfer function source receivers with a technique named in this paper as the Craig-Bampton stochastic method, which allows prediction of a nominal response and variations due to structural uncertainties as accurate as full Monte Carlo simulations but at a fraction of the computational effort. The paper then includes a statistical study of the data from the structural dynamic testing of the five identical craft of the Rapid-Eye constellation to set the magnitude of the uncertainties that should be applied in the analysis. Finally, the computational procedure is applied to the new high-resolution satellite SSTL-300-S1 and the predictions compared with the experimental results retrieved during the physical microvibration testing of the satellite, which was carried out at the Surrey Satellite Technology Limited facilities in the United Kingdom.
SSTL has been studying the application of its highly successful Low Earth Orbit micro and mini-satellites for lunar and planetary missions since 1996, through in-house funded design exercises and supported by ESA through Lunar and inner planet mission studies. Technical feasibility of a minisatellite lunar orbiter has been demonstrated. SSTL has since developed a range of improved subsystems and more advanced platforms, many of which have gained heritage in-orbit. These include the GMP-MiniSat platform with deployable solar arrays, accurate 3-axis stabilized attitude control, high resolution and wide field-of-view multispectral cameras and low cost bipropellant propulsion systems. Low cost launch options range from a Proton auxiliary payload launch direct to geostationary orbit, to prime passenger on a PSLV, to secondary payload alongside larger lunar missions. While SSTL is focused on low cost lunar orbiter development, it is jointly considering affordable means of conducting lunar landing, and ultimately sample return with the University of Surrey Space Centre. Lunar landing and sample return would demonstrate the applicability of low-cost small spacecraft technology to reduce the risk of high profile and barely affordable missions such as Mars Sample Return, by demonstrating key technologies, offering secondary science, and increased mission frequency to build enthusiastic public and political support. A parametric study for a lunar sample return mission from the south polar Aitken basin is highlighted, which has shown that a 15kg rover can in principle be landed on the lunar surface for a maximum surface stay of 150hours, subsequently returning a 200g sample to Earth, for a total launch mass from Earth orbit of less than 500kg, using a mixture of chemical and electric propulsion. This paper briefly considers the technology requirements and COTS technology availability for the separate mission stages, in order to establish how SSTL's low cost approach may be applicable to this challenging mission. This study is an ongoing area of research between SSTL and the University of Surrey Space centre.
M Sweeting, A O'Neill, J Remedios, B Golding, A Lewis, M Srokosz, H Bryden, A Lamb, H Balzter, G Smith, A Tewkesbury, JP Taylor, I Lisk, M Gibbs, H Langford, N Reynard, S Turner, T Wright, D Rosen, C Pilling, H Reeves, D Kerridge, S Loughlin, D MacDonald, A McKenzie,, R Ward, A Colenut, S Briggs, B Ryan, A Gillespie, A Lamb (2015)Observing the Earth – Expert views on environmental observation of the UK
The Royal Society
Observations of the physical and built environment are of critical importance to the UK, since the environment is directly tied to our national well-being, prosperity and security. Robust observing systems are vital for understanding, managing and forecasting environmental change. It is important that we capitalise on such observations to support decision making in Government with accurate and timely scientific evidence for the greatest public benefit.
Constella is a novel very quick response satellite platform that can be used in any Low Earth Orbit, It can be used as a single unit or as part of a constellation of spacecraft. It can be pre-manufactured to a large extent, and a selection of subsystems can be ready to select from, to provide last-minute configuration options for both the payload and platform. This satellite contains a number of innovations that have not been used in space before, and they will allow very quick response missions to take place. Only a very short time is required to decide on the mission and plan the satellite design, then assemble the final parts, and test and launch the satellite into orbit. The total time can be down to weeks or even days. Unlike most quick-response missions, where anything under one year is included, and where the satellite typically has to be completely ready and tested, waiting for quick call-up, the Constella can be tailored with interchangeable attitude sensors, propulsion units, communications equipment, payloads and more, just before launch, even right at the launch site if required. The platform produces almost the same amount electrical power, irrespective of orbital inclination or ascending node time, removing the need for solar panel design changes at the configuration stage.
This paper presents the results of a research project, which aims to investigate the suitability of advanced technologies to on-board computing. A generic single-chip computing platform for use on-board small spacecraft, which can be reconfigured remotely from the ground station, is proposed. The platform features a highly modular structure, such that it can be quickly and easily customised to produce specific-purpose controllers for data processing, communication and control of different spacecraft subsystems and payload blocks. Two schemes for on-board run-time partial reconfiguration are proposed, which will facilitate adding and updating of peripheral cores remotely (in space). The use of the Common Object Request Broker Architecture (CORBA) for remote reconfiguration of the computing platform over TCP/IP in LEO satellite constellations is detailed.
A control system is proposed for a low Earth orbit gravity gradient stabilised microsatellite using Z wheel. The microsatellite is 3-axis stabilized using a yaw reaction wheel, with dual redundant 3-axis magnetorquers. Two vector magnetometers and four dual sun sensors are carried in order to determine the full attitude. The attitude was estimated using an Euler angles (small libration version) on based extended Kalman filter (EKF). After the satellite has been detumbled and deploy the gravity gradient boom, in order to have the accurate Nadir pointing we will use the Z zero-bias mode controller. The Z momentum wheel will be damped by the magnetorquers. This paper describes the attitude determination and control system design of LEO microsatellite using Z reaction wheel for yaw phase mode control.
A new dimension of space mission architectures is emerging where hundreds to thousands of very small satellites will collectively perform missions in a distributed fashion. To support this architecture, high volume production of femto-scale satellites at low cost is required. This paper reviews current and emerging distributed space systems. A conceptual design of SpaceChip, which is a monolithic "satellite-on-a-chip" based on commercial CMOS technology is detailed. Assessment of the SpaceChip design is given and its use in future distributed space missions is discussed. Copyright © 2006 by ASME.
This paper describes a new high performance cost effective Earth Observation Platform, the SSTL-300 and associated optical sensor suite, offering a 7-year mission lifetime with a very high operational availability, for a mission cost an order of magnitude less than commercial high resolution Earth observation spacecraft. The paper will detail the SSTL-300 main payload, a very high-resolution imager with panchromatic multispectral channels. The paper will also outline an additional payload, the Medium Resolution Imager (MRI), which offers the widest swath of any comparable Earth Observation spacecraft. Earth images can be geolocated with high accuracy without the need for ground control points. Simultaneous high- and medium-resolution imaging is possible, coupled with either on-board lossless data compression for store-and-forward operations or near real-time imaging & down-linking for a range of targets close to the ground station. The SSTL-300 offers a range of imaging modes, including: strip mapping, fast response scene capture and stereo imaging offering swath widths up to 60km at high-resolution. Details of the nominal (sun-synchronous) orbit for the SSTL-300 will be provided stressing the balance between single spacecraft and constellation (multiple cooperating spacecraft) performance. The latter requires an accurate and reliable, yet low cost propulsion system which SSTL has developed, but is commonly featured on low cost small spacecraft.
Earth orbiting satellites come in a wide range of shapes and sizes to meet a diverse variety of uses and applications. Large satellites with masses over 1000kg support high resolution remote sensing of the Earth, high bandwidth communications services and world-class scientific studies but take lengthy developments and are costly to build and launch. The advent of commercially available, high-volume and hence low cost microelectronics has enabled a different approach through miniaturisation. This results in physically far smaller satellites that dramatically reduces timescales and costs and that are able to provide operational and commercially viable services. This paper charts the evolution and rise of small satellites from being an early curiosity with limited utility through to the present where small satellites are a key element of modern space capabilities.
P Davies, A Phipps, M Taylor, ADS Curiel, A Baker, Y Gao, M Sweeting, D Parker, IA Crawford, AJ Ball, L Wilson (2007)Uk lunar science missions: Moonlite & moonraker, In: 2007 3RD INTERNATIONAL CONFERENCE ON RECENT ADVANCES IN SPACE TECHNOLOGIES, VOLS 1 AND 2pp. 774-779
In the past several years, a plethora of spacecraft control techniques have been developed that address the challenging attitude tracking, stabilization and disturbance rejection requirements of these missions. One major aspect that has been typically missing in the research area of attitude control development is the experimental validation of the theoretical results. Experimental testing is necessary before control laws can be incorporated in the future generation of spacecraft. Based on this fact, we thought on the implementation of a software design COMSAT 1.0 that has the ability to overcome these difficulties. It includes all the attitude control phases, from the launcher separation i.e., initial attitude acquisition until the accurate nadir attitude pointing. This software uses micro satellites i.e., small satellites as testing models in orbit. We have chosen Alsat-1 the first Algerian micro satellite as a test model. © Medwell Journals, 2007.
Future Mars exploration missions will have increasingly ambitious goals compared to current rover and lander missions. There will be a need for extremely long distance traverses over shorter periods of time. This will allow more varied and complex scientific tasks to be performed and increase the overall value of the missions. The missions may also include a sample return component, where items collected on the surface will be returned to a cache in order to be returned to Earth, for further study. In order to make these missions feasible, future rover platforms will require increased levels of autonomy, allowing them to operate without heavy reliance on a terrestrial ground station. Being able to autonomously localise the rover is an important element in increasing the rover's capability to independently explore. This thesis develops a Planetary Monocular Simultaneous Localisation And Mapping (PM-SLAM) system aimed specifically at a planetary exploration context. The system uses a novel modular feature detection and tracking algorithm called hybrid-saliency in order to achieve robust tracking, while maintaining low computational complexity in the SLAM filter. The hybrid saliency technique uses a combination of cognitive inspired saliency features with point-based feature descriptors as input to the SLAM filter. The system was tested on simulated datasets generated using the Planetary, Asteroid and Natural scene Generation Utility (PANGU) as well as two real world datasets which closely approximated images from a planetary environment. The system was shown to provide a higher accuracy of localisation estimate than a state-of-the-art VO system tested on the same data set. In order to be able to localise the rover absolutely, further techniques are investigated which attempt to determine the rover's position in orbital maps. Orbiter Mask Matching uses point-based features detected by the rover to associate descriptors with large features extracted from orbital imagery and stored in the rover memory prior the mission launch. A proof of concept is evaluated using a PANGU simulated boulder field.
Detecting the health condition in vegetation is an important activity for many applications. Economically, most important is the prediction of crop yields and precision farming to reduce fertiliser use and increase yields worldwide. Monitoring natural forest resources and reserves is a growing interest with current changes in the earth’s climate. However this is not a simple task and normally requires aerial and field measurements that are limited and expensive. Continuous satellite coverage using small satellites in a DMC-like (Disaster Monitoring Constellation) configuration could provide a cost-effective answer to this problem combined with an improved low-cost hyperspectral instrument designed specifically for this task. Monitoring vegetation conditions using a satellite-borne remote sensing instrument presents some unique challenges. The “red-edge” is defined as the abrupt reflectance change caused by the combined effects of chlorophyll absorption and leaf internal scattering inside the 680 and 750 nm band. The shift of the point of maximum slope, called the red edge position (REP), has been correlated to the chlorophyll content of green vegetation in laboratory and field measurements. Furthermore the concept is controversial, as a majority consensus agree on the existence of a relationship between the chlorophyll content and the REP value. However, many scientists still do not see a significant improvement comparing to other traditional vegetation indices. [18, 23, 26] The fundamental basis for this research has been the evaluation of the “red-edge” effect as a suitable means for improving the detection and monitoring of vegetation parameters using a satellite-borne remote-sensing instrument. The feasibility of this approach was assessed by the development of a laboratory experiment to acquire spectral data from leaves and canopies in different health conditions. Then a computational radiometric analysis (included the acquisition modelling by several sensors) was conducted to simulate the passage through the atmosphere and be able to evaluate the impact over the signals. It was then possible to compare the results with previous research works and show that the solution could provide some benefit under a single canopy scenario for a range of applications. Key words: Hyperspectral, REP, red-edge, small satellites Email: email@example.com WWW: http://www.eps.surrey.ac.uk/
Spin-stabilised control was a pioneer spacecraft control method before a three-axis stabilised control was widely used. Spin-stabilised spacecraft, or spinner, uses this simple but robust method in controlling or manoeuvring the body in the microgravity environment. Surrey Space Centre (SSC) is currently spearheading the research in this area for a prolate shape spinner as a result of its involvement in the Moon Lightweight Interior and Telecoms Experiment (LITE) surface penetrator mission development funded by Astrium. The penetrator is a missile-shaped spacecraft used for delivering required mission equipment to the subsurface of the intended planet or celestial body. It is spin-stabilised after release from the orbiter before it is slewed to achieve a desired angle while free falling to the surface. The work described in the thesis is the ongoing development of the slew control algorithms by SSC as mentioned above. State-of-the-art algorithms have been developed, namely the Half-Cone (HC) derived family and pulse-train family. These algorithms have been proven theoretically, but implementation in a real-time mission is yet to be done, except for the Rhumb Line slew control. In particular, this thesis addresses the issue of the asymmetric shape of the developed prolate spacecraft where, in theory, it has been assumed as perfectly symmetric. Three new algorithms based on the HC-derived family that consider this asymmetric factor are discussed. The significant improvement made by these novel algorithms is the mass reduction of the final residual nutation in an average of one tenth of the current algorithm. Further analysis is done to these new algorithms in terms of accuracy, energy efficiency, slew time, the effect of thruster response time and gravity. The performance of these new algorithms in controlling an extreme asymmetric case is described first before it is applied to a common prolate-shaped spacecraft. An attempt to develop a testbed is also discussed within the work.