Craig Underwood

Professor Craig Underwood


Head of the Planetary Environments Group

Academic and research departments

Surrey Space Centre.

Biography

Biography

Prof. Craig I. Underwood graduated from the University of York in 1982 with a B.Sc. in Physics with Computer Science. After gaining a Post Graduate Certificate in Education in 1983, he began a teaching career at Scarborough Sixth-Form College where he developed satellite activities.In January 1986, Craig joined the University of Surrey as a Research Fellow/Engineer developing space education programmes and working on the UoSAT series of spacecraft, where he was responsible for the generation and maintenance of software for the UoSAT Satellite Control Ground-Station, mission analysis, thermal design and radiation environment and effects analysis and mitigation. From 1990 he has been Surrey's Principal Investigator of Space Radiation Environment and Effects, completing his PhD in this area in 1996.

In 1993, Craig became a Lecturer in Spacecraft Engineering advancing to Senior Lecturer in 1999, Reader in April 2003, and full Professor in April 2012. Craig was Deputy Director of the Surrey Space Centre from 2007 to 2014 and he currently heads the Environments and Instrumentation Group developing the concepts, instruments and techniques to investigate the Earth and other planetary environments from space.

Craig is author or co-author of some 200 scientific papers and teaches or has taught undergraduate and postgraduate courses on Spacecraft Engineering, Communications Payload Engineering, Satellite Remote Sensing, Planetary Exploration and Astronomy at the University of Surrey.

Research interests

• Radiation Environment & Effects (Cosmic Rays, Van Allan Belts, Space Weather, Atmospheric Radiation)• Remote Sensing Instrumentation (UV-VIS-NIR multi- and hyper-spectral imaging, Thermal IR imaging, UV-VIS-NIR radiometry and SWIR atmospheric spectroscopy, low-power SAR Radar, GNSS Reflectometry)• Micro-Nano-Satellite Technologies (SNAP, PalmSat, AAReST, RDV and Docking Systems)• Planetary Exploration (Mars VTOL Aerobot, Ramon Spectroscopy)• Space Power Systems (Supercapcitors, Thin-Film Solar PV, RTGs, solar-thermal power)PhD Topics are available in any of these or related areas.

The Group's personnel and their research interests can be seen here.

Craig heads the Environments and Instrumentation Group within the Surrey Space Centre, which has the remit of developing the instruments, systems and data processing techniques needed to investigate the Earth and other planetary environments from space. A particular focus of the group is on the development of low-mass, low-volume and low-power “micro-instrumentation” suitable for use on micro/nano-satellite technology platforms. Current research activities include the analysis of the space and atmospheric radiation environments and their effects on commercial-off-the-shelf (COTS) avionic technologies; the development of miniaturised instrumentation for ionising-radiation detection, UV-VIS-NIR and thermal-IR satellite remote sensing; micro-satellite-based radar imaging; a Mars VTOL unpopulated micro-air-vehicle, and micro-nano-satellite technologies.

 

Radiation Environment & EffectsOver the past 25 years Craig has gained considerable expertise in understanding the space radiation environment and its effects in low, medium and high Earth orbit (out to 60,000 km). The deleterious effects of the ionising radiation environment is of particular concern when using COTS technologies in space, thus, particular emphasis has been given to a programme of monitoring “space weather” in terms of the high energy proton and heavy-ion cosmic-ray environment these spacecraft encounter, and to observing and analysing its effects - particularly with regard to single-event effects - upon the COTS devices on-board. The extended period of research has enabled a wide variety of conditions to be observed ranging across an entire solar cycle, and standard models to be verified or challenged. He was the first to show clearly the effect of the SAA trapped proton environment on COTS memories operating in LEO (UoSAT-2), and through his work with QinetiQ using the QinetiQ's CREDO (UoSAT-3) and his own CRE (KITSAT-1, PoSAT-1) instruments has shown the limitations of the AP8 and CREME models. He is now performing similar work for the MEO environment through the analysis of flight data from Surrey's CEDEX and QinetiQ's MERLIN payloads flown on GIOVE-A. It has recently delivered two miniaturised radiation monitors (MuREM, RM) for the UK's TechDemoSat-1 mission, launched in 2014. These payloads comprise solid-state (RadFET) dosimeters, ionizing dose-rate-diode detectors, and PIN-diode -based multi-channel analysers for measuring proton and heavy-ion LET spectra. The work has also been applied to the aerospace sector via the SPACERANE project.

Remote Sensing InstrumentationOptical: Craig has had a long-term interest in remote sensing instrumentation design: He developed stratospheric ozone monitoring UV radiometers for the FASAT-Alfa (1995) and FASAT-Bravo (1998) satellites, and an ultra-compact Earth-observation CMOS video camera for the Thai Paht (1998) satellite. He also provided the pre-flight optical and radiometric calibration of the tri-band (NIR, Red, Green) imaging sensors for the Disaster Monitoring Constellation (DMC) Satellites: AlSAT-1 (2002, UK-DMC (2003) and NigeriaSat (2003).With his PhD students, Craig has developed prototype designs for a micro-bolometer array-based thermal-IR imager (B. Olerich, 2005) and for a UV spectrometer for monitoring volcanic plumes (SO2) and ozone (J. Fernandez-Saldivar, 2008). He has a strong interest in the application of Spatial Heterodyne Spectroscopy (SHS) and, through PhD studies, has applied this technique to an ultra-compact Ramon spectrometer for the analysis of Martian rocks (T. Nathanial,2011) and to the SWIR detection and measurement of atmospheric CO2 (I. Ikpaya, 2013). He is also interested in compact hyperspecteral instruments for micro-sat and UAV application.

Radar: He has proposed a bistatic Synthetic Aperture Radar (SAR) imaging concept for micro-satellites (2000) and, through PhD programmes, has developed the concept of applying low-power CWFM bi-static and mono-static SAR to micro-sat platforms (~100-150kg) (O. Mitchell, 2001; T. Wanwiwake, 2011; N. Ahmed, 2012; A. Cai, 2013). He also worked on the airborne demonstrator for the NovaSAR S-Band SAR (2010).He has also supported PhD research into GNSS Reflectometry (P. Jales, 2013; E. Simons, 2014; J. Tye); Image Data Compression (P. Hou, 1999); Machine Vision for Pose and Relative Orbit estimation (A. Cropp, 2001); and working with the National Physical Laboratory is researching Vicarious Calibration/Validation of Remote Sensing Instruments and Radiometric Uncertainty modelling (A. Bialek, J. Gorrono).Micro-Nano-Satellite Technologies.

Craig began Surrey's nano-satellite activities in 1995, through setting and supervising a series of student projects aimed at developing a "soccer ball" sized spacecraft. As Chief Architect of the SNAP concept, he played a pioneering role in developing the UK's first operational nano-satellite, SNAP-1, Surrey's 6.5 kg nano-satellite, launched in June 2000, which carried out experiments in autonomous orbital manoeuvring and remote inspection of other spacecraft. For his work on SNAP, Craig and the Surrey Space Centre achieved the award of “Finalist” in the 2001 Flight International Awards in the Space and Missiles Category. He subsequently developed the PalmSat, ~1kg pico-satellite concept in 2000, designed to play a similar rôle, and he is currently the UK PI for the AAReST multiple-mirror space telescope demonstrator concept, working with CalTech/NASA-JPL, where he is also developing a novel electro-magnetic rendezvous and docking system. AAReST is designed to demonstrate the autonomous in-orbit construction of a space telescope using multiple-mirror elements, which can change shape to form a coherent optical surface. Craig has also worked on Super-Capacitor based power systems (T. Shimizu, 2013); Thin-film solar PV systems; data-handling and RF systems (V.Asenek, 1998; S. Maqbool, 2006).Planetary Exploration

Away from orbit, Craig is working on a vertical take-off and landing (VTOL) “flying wing” aerobot concept for the exploration of Mars (J. Fielding, 2004; H. Song, 2008; W. Zhao, 2013; N. Collins, current). He has also worked on studies for Lunar microsatellite missions, spaceborne radio astronomy, Mars sample returns and NEO investigations,

Teaching

Over the last 30 years, Craig has played a key role in developing and teaching Surrey's Spacecraft Engineering post-graduate, undergraduate and industrial-training courses. He was the recipient of the Department of Electrical and Electronic Engineering's Tony Jeans Inspirational Teaching Prize, 2013. Currently he teaches:

• Level 1 (FHEQ 4) Mathematics• Level 2 (FHEQ 5) Space Engineering and Mission Design• Level 3 (FHEQ 6) Space Systems Design• Level M (FHEQ 7) Spacecraft Systems Design• Level M (FHEQ 7) Launch Vehicles and Propulsion• Level M (FHEQ 7) Space Environment and Protection• Short Course: Spacecraft Systems Design

My publications

Publications

Fernandez-Saldivar JA, Underwood CI, Mackin S (2006) Low-cost microsatellite UV instrument suite for monitoring ozone and volcanic sulphur dioxide, REMOTE SENSING OF CLOUDS AND THE ATMOSPHERE XI 6362 SPIE-INT SOC OPTICAL ENGINEERING
Shimizu T, Underwood C (2013) Super-capacitor energy storage for micro-satellites: Feasibility and potential mission applications, ACTA ASTRONAUTICA 85 pp. 138-154 PERGAMON-ELSEVIER SCIENCE LTD
Crocombe AD, Wang R, Richardson G, Underwood CI (2006) Estimating the energy dissipated in a bolted spacecraft at resonance, COMPUTERS & STRUCTURES 84 (5-6) pp. 340-350 PERGAMON-ELSEVIER SCIENCE LTD
Taylor BO, Underwood CI, Vacanti G, Maddox E (2011) The Interplanetary Electron Model (IEM), IEEE Transactions on Nuclear Science 6 (58) pp. 2785-2792 IEEE
A new Interplanetary electron environment model based on statistical analyses of historical datasets is presented. The model reports generates confidence limits for solar electron fluences in a similar fashion to existing Solar proton models, as well as peak event fluxes and fluences. Electrons of Jovian origin are also modeled based on simplified diffusive transport equations to provide predicted fluxes for locations within the ecliptic plane.
Lamb DA, Irvine SJC, Clayton AJ, Kartopu G, Barrioz V, Hodgson SD, Baker MA, Grilli R, Hall J, Underwood CI, Kimber R (2016) Characterization of MOCVD Thin-Film CdTe Photovoltaics on Space-Qualified Cover Glass, IEEE Journal of Photovoltaics 6 (2) pp. 557-561 IEEE
This paper details the AM0 conversion efficiency of a metal-organic chemical vapor phase deposition thin-film cadmium telluride (CdTe) solar cell deposited onto a cerium-doped cover glass (100 ¼m). An AM0 best cell conversion efficiency of 12.4% (0.25-cm2 contact area) is reported. An AM0 mean efficiency of 12.1% over eight cells demonstrated good spatial uniformity. Excellent adhesion of the cell structure to the cover glass was observed with an adhesive strength of 38 MPa being measured before cohesive failure of the test adhesive. The device structure on cover glass was also subject to severe thermal shock cycling of +80 °C to -196 °C, showing no signs of delamination and no deterioration of the photovoltaic (PV) performance.
Taylor B, Underwood Craig, Evans HDR, Ryden Keith, Rodgers D, Daly EJ, Mandorlo G, Falcone M, Morris PA, Prieto RG (2007) Results from the Galileo giove - A radiation monitors and comparison with existing radiation belt models, IEEE TRANSACTIONS ON NUCLEAR SCIENCE 54 (4) pp. 1076-1081 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
The radiation monitors on board the Galileo Giove-A satellite, CEDEX and Merlin, and their data are presented. The instruments include energetic proton and ion detectors, an internal charging monitor, RADFETs and experimental dose-rate photodiodes. A comparison of the data with existing monitors and models is presented.
Saaj C, Underwood C, Noakes C, Park D, Moore T (2008) The science and technology behind Galileo - Europe's GPS, JBIS-JOURNAL OF THE BRITISH INTERPLANETARY SOCIETY 61 (3) pp. 91-97 BRITISH INTERPLANETARY SOC
Ryden Keith, Morris PA, Ford KA, Hands ADP, Dyer CS, Taylor B, Underwood Craig, Rodgers DJ, Mandorlo G, Gatti G, Evans HDR, Daly EJ (2008) Observations of Internal Charging Currents in Medium Earth Orbit, IEEE TRANSACTIONS ON PLASMA SCIENCE 36 (5) pp. 2473-2481 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Underwood Craig, Pellegrino Sergio, Lappas Vaios, Bridges Christopher, Taylor Benjamin, Chhaniyara Savan, Theodorou Theodoros, Shaw Peter, Arya Manan, Breckinridge James, Hogstrom Kristina, Patterson Keith D., Steeves John, Wilson Lee, Horri Nadjim (2013) Autonomous Assembly of a Reconfigurable Space Telescope (AAReST) ? A CubeSat/Microsatellite Based Technology Demonstrator, Proceedings of the 27th Annual AIAA/USU Conference on Small Satellites (SmallSat 2013) American Institute of Aeronautics and Astronautics (AIAA)
Future space telescopes with diameter over 20 m will require in-space assembly. High-precision formation flying has very high cost and may not be able to maintain stable alignment over long periods of time. We believe autonomous assembly is a key enabler for a lower cost approach to large space telescopes. To gain experience, and to provide risk reduction, we propose a demonstration mission to demonstrate all key aspects of autonomous assembly and reconfiguration of a space telescope based on multiple mirror elements. 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 ?9U? class nanosatellite core, which houses two fixed mirrors and a boom-deployed focal plane assembly. All three spacecraft will be launched as a single ~40kg microsatellite package.
Bridges CP, Kenyon S, Underwood CI, Sweeting MN (2011) STRaND: Surrey Training Research and Nanosatellite Demonstrator, Proceedings of the1st IAA Conference on University Satellite Missions and CubeSat Workshop International Academy of Astronautics
Gao S, Clark K, Unwin M, Zackrisson J, Shiroma WA, Akagi JM, Maynard K, Garner P, Boccia L, Amendola G, Massa G, Underwood C, Brenchley M, Pointer M, Sweeting MN (2009) Antennas for Modern Small Satellites, IEEE ANTENN PROPAG M 51 (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.
Bridges C, Kenyon S, Underwood C, Lappas V (2011) STRaND-1: The world's first smartphone nanosatellite, 2nd International Conference on Space Technology, ICST 2011
Space researchers at the University of Surrey and Surrey Satellite Technology Limited (SSTL) have developed 'STRaND-1', a satellite containing a smartphone payload that will be launched into orbit around the Earth later this year. STRaND-1 (Surrey Training, Research and Nanosatellite Demonstrator) is being developed by the Surrey team to demonstrate the advanced capabilities of a satellite built quickly using advanced commercial off-the-shelf components. The satellite will be launched into orbit around the Earth in 2011. The phone will run on Android's powerful open-source operating system. A powerful computer, built at the Surrey Space Centre, will test the vital statistics of the phone once in space. The computer will check which components of the phone are working normally and will relay images and messages back to Earth via a radio system. Once all the tests are complete, the plan is to switch off the micro computer and the smartphone will be used to operate parts of the satellite. The smartphone avionics suite is only one of the many technological advances packed into this 4kg satellite. To precisely point and manoeuvre, the satellite also incorporates advanced guidance, navigation and control systems. © 2011 IEEE.
Di Bari R, Brown T, Gao S, Notter M, Hall D, Underwood C (2011) Dual-Polarized Printed S-Band Radar Array Antenna for Spacecraft Applications, IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS 10 pp. 987-990 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Wang R, Crocombe AD, Richardson G, Underwood CI (2008) Energy dissipation in spacecraft structures incorporating bolted joints operating in macroslip, JOURNAL OF AEROSPACE ENGINEERING 21 (1) pp. 19-26 ASCE-AMER SOC CIVIL ENGINEERS
Zhao W, Underwood C (2014) Robust transition control of a Martian coaxial tiltrotor aerobot, ACTA ASTRONAUTICA 99 pp. 111-129 PERGAMON-ELSEVIER SCIENCE LTD
Fernandez-Saldivar JA, Underwood CI, Mackin S (2008) Comparison of atmospheric ozone measurements between NASA's Total Ozone Mapping Spectrometer (TOMS) and the FASAT-BRAVO Ozone Mapping Detector (OMAD), SMALL SATELLITES FOR EARTH OBSERVATION: SELECTED CONTRIBUTIONS pp. 101-109 SPRINGER
Wang R, Crocombe AD, Richardson G, Underwood CI (2008) Energy dissipation in spacecraft structures incorporating bolted joints with viscoelastic layers, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART G-JOURNAL OF AEROSPACE ENGINEERING 222 (G2) pp. 201-211 PROFESSIONAL ENGINEERING PUBLISHING LTD
Ryden KA, Hands ADP, Underwood CI, Rodgers DJ (2015) Internal Charging Measurements in Medium Earth Orbit Using the SURF Sensor: 2005-2014, IEEE TRANSACTIONS ON PLASMA SCIENCE 43 (9) pp. 3014-3020 IEEE
Taylor B, Underwood C, Evans HDR, Daly E, Ryden KA, Santin G (2008) Galileo GIOVE-A MEORAD Results and Analysis, IEEE TRANSACTIONS ON NUCLEAR SCIENCE 55 (6) pp. 3151-3157 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Ahmed N, Underwood CI (2010) Software Defined LFM CW SAR Receiver for Microsatellites, SMALL SATELLITE MISSIONS FOR EARTH OBSERVATION pp. 311-320 SPRINGER-VERLAG BERLIN
Di Bari R, Brown TWC, Gao S, Underwood C (2011) Dual-Polarized Printed S-Band Radar Array Antenna for Spacecraft Applications, IEEE Antennas and Wireless Propagation Letters 10 pp. 987-990 IEEE
A novel dual-polarized broadband antenna array for S-band is presented. This antenna is composed of 6 × 2 microstrip antenna elements with a hybrid feed-line network providing an isolation e 18.6 dB between the H- and V-ports. The operative bandwidth is from 3.15 to 3.25 GHz, and the peak measured gain is approximately 19 dBi. The array is suitable for spacecraft operation because of the selected materials, its low profile (~8 mm thickness), and light weight. It has potential applications in synthetic aperture radar (SAR), remote sensing, and wireless communications.
Cai A, Underwood C, Sweeting MN (2013) Height reduction using mutual coupling for the multimode horn phased array, 2013 7th European Conference on Antennas and Propagation, EuCAP 2013 pp. 3585-3589
A novel approach is presented that demonstrates the advantage of mutual coupling in reducing the height of the multimode horn. It is found that this method can reduce the height by an additional 0.4» for the 3»×3» horn aperture and produce a smaller active element volume for the same gain in isolation and above the 81% efficiency from 8.8 GHz to 10.2 GHz for the infinite array. The mode matching model (infinite array) and Ansoft HFSS simulator (3×3 finite array) are used to demonstrate this feasibility. © 2013 EurAAP.
Hands A, Ryden K, Underwood C, Rodgers D, Evans H (2015) A New Model of Outer Belt Electrons for Dielectric Internal Charging (MOBE-DIC), IEEE TRANSACTIONS ON NUCLEAR SCIENCE 62 (6) pp. 2767-2775 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Bridges CP, Taylor B, Horri N, Underwood CI, Kenyon S, Barrera-Ars J, Pryce L, Bird R (2013) STRaND-2: Visual Inspection, Proximity Operations &
Nanosatellite Docking,
The Surrey Training Research and Nanosatellite
Demonstrator (STRaND) programme has been success in identifying and creating a leading low-cost nanosatellite programme with advanced attitude and orbit control system (AOCS) and experimental computing platforms based on smart-phone technologies. The next demonstration capabilities, that provide a challenging mission to the existing STRaND platform, is to perform visual inspection, proximity operations and nanosatellite docking. Visual inspection is to be performed using a COTS LIDAR system to estimate range and pose under 100 m. Proximity operations are controlled using a comprehensive guidance, navigation and control (GNC) loop in a polar form of the Hills Clohessy Wiltshire (HCW) frame
including J2 perturbations. And finally, nanosatellite docking is performed at under 30 cm using a series of tuned magnetic coils. This paper will document the initial experiments and
calculations used to qualify LIDAR components, size the mission thrust and tank requirements, and air cushion table demonstrations of the docking mechanism.
Smail S, Underwood CI (2009) ELECTROMAGNETIC FLAT DOCKING SYSTEM FOR IN-ORBIT SELF-ASSEMBLY OF SMALL SPACECRAFT, SPACEFLIGHT MECHANICS 2009, VOL 134, PTS I-III 134 pp. 173-183 UNIVELT INC
Song H, Underwood C (2007) A Mars VTOL aerobot - Preliminary design, dynamics and control, 2007 IEEE AEROSPACE CONFERENCE, VOLS 1-9 pp. 204-217 IEEE
Lamb DA, Irvine SJC, Clayton AJ, Barrioz V, Kartopu G, Baker MA, Underwood CI, Grilli R, Kimber R, Hall J (2015) Lightweight and low-cost thin film photovoltaics for large area extra-terrestrial applications, IET RENEWABLE POWER GENERATION 9 (5) pp. 420-423 INST ENGINEERING TECHNOLOGY-IET
Maqsood, M, Gao S, Brown TWC, Unwin M, de vos Van Steenwijk R, Xu JD, Underwood CI (2014) Low-Cost Dual-Band Circularly Polarized
Switched-Beam Array for Global Navigation
Satellite System,
IEEE Transactions on Antennas and Propagation 62 (4) pp. 1-8
This paper presents the design and development of
a dual-band switched-beam microstrip array for Global Navigation Satellite System (GNSS) applications such as ocean reflectometry and remote sensing. In contrast to the traditional Butler matrix, a simple, low cost, broadband and low insertion loss beam switching feed network is proposed, designed and integrated with a dual band antenna array to achieve continuous beam coverage of ±25° around the boresight at the L1 (1.575 GHz) and L2 (1.227 GHz) bands. To reduce the cost, microstrip lines and PIN diode based switches are employed. The proposed switched beam network is then integrated with dual-band step-shorted annular ring (S-SAR) antenna elements in order to produce a fully integrated compact-sized switched beam array. Antenna simulation results show that the switched beam array achieves a maximum gain of 12 dBic at the L1 band and 10 dBic at the L2 band. In order to validate the concept, a scaled down prototype of the simulated design is fabricated and measured. The prototype operates at twice of the original design frequency i.e. 3.15 GHz and 2.454 GHz and the measured results confirm that the integrated array achieves beam switching and good performance at both bands.
Taylor B, Underwood CI, Ryden KA, Morris PA (2009) A GIOVE Derived Galileo Electron Spectrum and Comparison to Models, IEEE TRANSACTIONS ON NUCLEAR SCIENCE 56 (6) pp. 3423-3428 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Fernandez-Saldivar JA, Underwood CI, Mackin S (2007) Ozone depletion in the Austral spring from UV microsatellite instrument - art. no. 674503, REMOTE SENSING OF CLOUDS AND THE ATMOSPHERE XII 6745 pp. 74503-74503 SPIE-INT SOC OPTICAL ENGINEERING
Taylor B, Underwood C, Dyer A, Ashton C, Rason S, Browning J (2012) The micro radiation environment monitor (MuREM) and SSTL radiation monitor (SSTL RM) on TechDemoSat-1, IEEE Transactions on Nuclear Science 59 (4 PART 1) pp. 1060-1065
Two new miniaturized scientific radiation monitoring payloads are presented prior to their first flight on the TechDemoSat-1 Spacecraft. They are capable of monitoring the space radiation environment and its effects on radiation-sensitive devices. Micro radaion environment monitor (MuREM) and Surrey Satellite Technology radiation monitor (SSTL RM) carry RADFET dosimeters, dose-rate-sensitive photodiodes, and p-i-n diode particle detectors. SSTL RM is also connected to external RADFET sensors placed around the spacecraft, while MuREM carries a radiation effects payload consisting of COTS devices that will be monitored while exposed to the space radiation environment. © 2012 IEEE.
Taylor BO, Duke R, Stewart B, Massimiani C, Djamane F, Bridges CP, Aglietti GS, Lassakeur A, Amine Ouisb M, Cherif Ladouze M, Meftah K, Underwood CI, Chikouche A, Hamed D (2017) AlSat-Nano: Knowledge Transfer to Operational Partnership, 68th International Astronautical Congress Proceedings International Astronautical Federation
The AlSat-Nano mission is a joint endeavour by the UK and Algeria to build and operate a 3U CubeSat. The project was designed to provide training to Algerian students, making use of UK engineering and experience. The CubeSat was designed and built by the Surrey Space Centre (SSC) of the University of Surrey and hosts three UK payloads with operations run by the Algerian Space Agency (ASAL). The educational and CubeSat development were funded by the UK Space Agency (UKSA), whilst the UK payloads were self-funded. Launch and operations are funded by ASAL. This paper illustrates the development of the programme, the engineering of the satellite and the development of collaborative operations between the SSC and ASAL.
Lamb Dan A., Underwood Craig, Barrioz Vincent, Gwilliam Russell, Hall James, Baker Mark, Irvine Stuart J. C. (2017) Proton Irradiation of CdTe Thin Film Photovoltaics Deposited on Cerium-Doped Space Glass, Progress in Photovoltaics 25 (12) pp. 1059-1067 Wiley
Space photovoltaics is dominated by multi-junction (III-V) technology. However, emerging
applications will require solar arrays with; high specific power (kW/kg), flexibility in
stowage and deployment and a significantly lower cost than the current III-V technology
offers. This research demonstrates direct deposition of thin film CdTe onto the radiation-hard
cover glass that is normally laminated to any solar cell deployed in space. Four CdTe
samples, with 9 defined contact device areas of 0.25 cm2, were irradiated with protons of 0.5
MeV energy and varying fluences. At the lowest fluence, 1×1012 cm-2, the relative efficiency
of the solar cells was 95%. Increasing the proton fluence to 1×1013 cm-2 and then 1×1014 cm-2
decreased the solar cell efficiency to 82% and 4% respectively. At the fluence of 1×1013 cm-2,
carrier concentration was reduced by an order of magnitude. Solar Cell Capacitance
Simulator (SCAPS) modelling obtained a good fit from a reduction in shallow acceptor
concentration with no change in the deep trap defect concentration. The more highly
irradiated devices resulted in a buried junction characteristic of the external quantum
efficiency, indicating further deterioration of the acceptor doping. This is explained by
compensation from interstitial H+ formed by the proton absorption. An anneal of the 1×1014
cm-2 fluence devices gave an efficiency increase from 4% to 73% of the pre-irradiated levels,
indicating that the compensation was reversible. CdTe with its rapid recovery through
annealing, demonstrates a radiation hardness to protons that is far superior to conventional
multi-junction III-V solar cells.
Gorrono J, Banks A, Gascon F, Fox N, Underwood CI (2016) Novel techniques for the analysis of the TOA radiometric uncertainty, Proceedings of SPIE
In the framework of the European Copernicus programme, the European Space Agency (ESA) has launched the Sentinel-2 (S2) Earth Observation (EO) mission which provides optical high spatial -resolution imagery over land and coastal areas. As part of this mission, a tool (named S2-RUT, from Sentinel-2 Radiometric Uncertainty Tool) estimates the radiometric uncertainties associated to each pixel using as input the top-of-atmosphere (TOA) reflectance factor images provided by ESA. The initial version of the tool has been implemented ? code and user guide available1 ? and integrated as part of the Sentinel Toolbox. The tool required the study of several radiometric uncertainty sources as well as the calculation and validation of the combined standard uncertainty in order to estimate the TOA reflectance factor uncertainty per pixel. Here we describe the recent research in order to accommodate novel uncertainty contributions to the TOA reflectance uncertainty estimates in future versions of the tool. The two contributions that we explore are the radiometric impact of the spectral knowledge and the uncertainty propagation of the resampling associated to the orthorectification process. The former is produced by the uncertainty associated to the spectral calibration as well as the spectral variations across the instrument focal plane and the instrument degradation. The latter results of the focal plane image propagation into the provided orthoimage. The uncertainty propagation depends on the radiance levels on the pixel neighbourhood and the pixel correlation in the temporal and spatial dimensions. Special effort has been made studying non-stable scenarios and the comparison with different interpolation methods
Hands A, Lei F, Ryden KA, Dyer C, Underwood CI, Mertens C (2016) New Data and Modelling for Single Event Effects in the Stratospheric Radiation Environment, IEEE Transactions on Nuclear Science 64 (1) pp. 587-595 IEEE
The upper atmosphere is a transition region between the neutron-dominated aviation environment and satellite environment where primary protons and ions dominate. We report high altitude balloon measurements and model results characterising this radiation environment for single event effects (SEE) in avionics. Our data, from the RaySure solid-state radiation monitor, reveal markedly different altitude profiles for low linear energy transfer (LET) and high LET energy depositions. We use models to show that the difference is caused by the influence of primary cosmic ray particles, which induce counts in RaySure via both direct and indirect ionization. Using the new Model of Atmospheric Ionizing Radiation Effects (MAIRE), we use particle fluxes and LET spectra to calculate single event upset (SEU) rates as a function of altitude from ground level to the edge of space at 100 km altitude. The results have implications for a variety of applications including high altitude space tourism flights, UAVs and missions to the Martian surface.
Gorrono J, Banks A, Fox N, Underwood CI (2017) Radiometric inter-sensor cross-calibration uncertainty using a traceable high accuracy reference hyperspectral imager, ISPRS Journal of Photogrammetry and Remote Sensing 130 pp. 393-417 Elsevier
Optical earth observation (EO) satellite sensors generally suffer from drifts and biases relative to their pre-launch calibration, caused by launch and/or time in the space environment. This places a severe limitation on the fundamental reliability and accuracy that can be assigned to satellite derived information, and is particularly critical for long time base studies for climate change and enabling interoperability and Analysis Ready Data. The proposed TRUTHS (Traceable Radiometry Underpinning Terrestrial and Helio-Studies) mission is explicitly designed to address this issue through re-calibrating itself directly to a primary standard of the international system of units (SI) in-orbit and then through the extension of this SI-traceability to other sensors through in-flight cross-calibration using a selection of Committee on Earth Observation Satellites (CEOS) recommended test sites. Where the characteristics of the sensor under test allows, this will result in a significant improvement in accuracy. This paper describes a set of tools, algorithms and methodologies that have been developed and 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. In this study, Multi-Spectral Imager (MSI) of Sentinel-2 and Landsat-8 Operational Land Imager (OLI) is evaluated as an example, however the analysis is readily translatable to larger-footprint sensors such as Sentinel-3 Ocean and Land Colour Instrument (OLCI) and Visible Infrared Imaging Radiometer Suite (VIIRS). This study considers the criticality of the instrumental and observational characteristics on pixel level reflectance factors, within a defined spatial region of interest (ROI) within the target site. It quantifies the main uncertainty contributors in the spectral, spatial, and temporal domains. The resultant tool will support existing sensor-to-sensor cross-calibration activities carried out under the auspices of CEOS, and is also being used to inform the design specifications for TRUTHS.
Gorrono J, Fomferra N, Peters M, Gascon F, Underwood CI, Fox N, Kirches G, Brockmann C (2017) A Radiometric Uncertainty Tool for the Sentinel 2 Mission, Remote Sensing 9 (178) MDPI AG
In the framework of the European Copernicus programme, the European Space Agency (ESA) has launched the Sentinel-2 (S2) Earth Observation (EO) mission which provides optical high spatial resolution imagery over land and coastal areas. As part of this mission, a tool (named S2-RUT, from Sentinel-2 Radiometric Uncertainty Tool) has been developed. The tool estimates the radiometric uncertainty associated with each pixel in the top-of-atmosphere (TOA) reflectance factor images provided by ESA. This paper describes the design and development process of the initial version of the S2-RUT tool. The initial design step describes the S2 radiometric model where a set of uncertainty contributors are identified. Each of the uncertainty contributors is specified by reviewing the preand post-launch characterisation. The identified uncertainty contributors are combined following the guidelines in the ?Guide to Expression of Uncertainty in Measurement? (GUM) model and this combination model is further validated by comparing the results to a multivariate Monte Carlo Method (MCM). In addition, the correlation between the different uncertainty contributions and the impact of simplifications in the combination model have been studied. The software design of the tool prioritises an efficient strategy to read the TOA reflectance factor images, extract the auxiliary information from the metadata in the satellite products and the codification of the resulting uncertainty image. This initial version of the tool has been implemented and integrated as part of the Sentinels Application Platform (SNAP).
Ahmad G, Brown TWC, Underwood CI, Loh T (2017) An efficient algorithm for electrically large reflectarray antenna design automation, Proceedings of the 2017 International Workshop on Electromagnetics: Applications and Student Innovation Competition pp. 133-134 IEEE
Reflectarrays are becoming a potentially attractive replacement of parabolic reflectors for high gain requirements. A large reflectarray consists of thousands of elements. To predict their performance a simulation model is required which is very cumbersome to build manually due to a large number of elements. It takes exhaustive efforts, keen attention to details and significant amount of time to build such a simulation model. When several iterations of modelling are required it worsens the issue even further. We have presented here an algorithm as an automated solution to this problem by interfacing Matlab® with an electromagnetic simulation software. It is very generic, time efficient and makes the modelling easy with least intervention of the designer.
Ahmad G, Loh T, Brown TWC, Underwood CI (2017) On the Phase Selection of Millimeter Wave Quantized Reflectarrays, Proceedings of the 2017 International Applied Computational Electromagnetics Society Symposium IEEE
Microstrip printed reflectarrays are becoming a potential replacement of parabolic reflector and phased array antennas due to their simple design, low cost and ease of manufacture to attain high gain and wide angle beam pointing at millimeter waves (mm-waves). Significant challenges are faced while implementing continuous phase reflectarrays at mm-waves. However, discretizing the required reflection phase provides a practically implementable solution. This contribution addresses the selection of phase states and its scattering in a phase discretized mm-wave reflectarray. The performance of two 1.5 bit phase quantized reflectarrays having closely spaced geometrical features is analyzed at 60 GHz. This study provides a better understanding to achieve a wider bandwidth response in practically implementable mm-wave reflectarrays.
Ahmad G, Brown TWC, Underwood CI, Loh T (2017) How coarse is too coarse in electrically large reflectarray smart antennas?, Proceedings of the 2017 International Workshop on Electromagnetics: Applications and Student Innovation Competition pp. 135-137 IEEE
Millimeter wave (mm-wave) bands are becoming potentially attractive candidates for next generation communication systems. It is envisioned that high gain smart antennas will be one of the key enabling technologies for such systems. At mm-wave bands, where electrical size of an individual antenna becomes very small, the inclusion of a reconfigurable mechanism in the antenna becomes a great challenge due to real estate constraints. In these scenarios a designer has to decide on the number of bits in a phase shifter for antenna beam steering which will result in an optimum design. This contribution addresses the issue of phase quantization in mm-wave high gain reflectarray smart antennas to achieve an optimum performance. Implementing coarse phase quantization greatly reduces the complexity at mm-wave bands. A case study is presented to highlight the effects of coarse phase quantization using various numbers of bits.
Lamb DA, Underwood Craig, Barrioz V, Gwilliam Russell, Hall James, Baker Mark, Irvine SJC (2017) Proton irradiation of CdTe thin film photovoltaics deposited on
cerium?doped space glass,
Progress in Photovoltaics 25 (12) pp. 1059-1067 Wiley
Space photovoltaics is dominated by multi?junction (III?V) technology. However, emerging applications
will require solar arrays with high specific power (kW/kg), flexibility in stowage and
deployment, and a significantly lower cost than the current III?V technology offers. This research
demonstrates direct deposition of thin film CdTe onto the radiation?hard cover glass that is normally
laminated to any solar cell deployed in space. Four CdTe samples, with 9 defined contact
device areas of 0.25 cm2, were irradiated with protons of 0.5?MeV energy and varying fluences.
At the lowest fluence, 1 × 1012 cm?2, the relative efficiency of the solar cells was 95%. Increasing
the proton fluence to 1 × 1013 cm?2 and then 1 × 1014 cm?2 decreased the solar cell efficiency to
82% and 4%, respectively. At the fluence of 1 × 1013 cm?2, carrier concentration was reduced by
an order of magnitude. Solar Cell Capacitance Simulator (SCAPS) modelling obtained a good fit
from a reduction in shallow acceptor concentration with no change in the deep trap defect concentration.
The more highly irradiated devices resulted in a buried junction characteristic of the
external quantum efficiency, indicating further deterioration of the acceptor doping. This is
explained by compensation from interstitial H+ formed by the proton absorption. An anneal of
the 1 × 1014 cm?2 fluence devices gave an efficiency increase from 4% to 73% of the pre?irradiated
levels, indicating that the compensation was reversible. CdTe with its rapid recovery through
annealing demonstrates a radiation hardness to protons that is far superior to conventional multijunction
III?V solar cells.
Eckersley S, Saunders C, Lobb D, Johnston G, Baud T, Sweeting MN, Underwood CI, Bridges CP, Chen R (2017) Future Rendezvous and Docking Missions enabled by low-cost but safety compliant Guidance Navigation and Control (GNC) architectures, Proceedings of The 15th Reinventing Space Conference British Interplanetary Society
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
Ahmad G, Brown T, Underwood C, Loh T (2017) Millimetre Wave Reflectarray Antenna Unit Cell Measurements, LAPC 2017 Proceedings Institution of Engineering and Technology
Reflectarray antennas are a potential candidate solution to realize high gains at millimetre waves (mm-waves). A reflectarray contains a large number of spatially illuminated unit cells. The performance of a good reflectarray design is manifested by the behaviour of its comprising unit cells. An established technique to characterise a unit cell is by placing it inside a waveguide to achieve periodic boundary conditions. This usually requires custom waveguide products; making the tests difficult and expensive. Additionally, when the unit cells are reconfigurable as in a smart reflectarray it is hard to take the DC bias lines out of the waveguide without using custom made waveguide parts. This contribution address the issue of unit cell placement inside the waveguide and proposes simple unit cell structures to avoid custom made waveguide parts. The idea was verified by measuring a series of unit cells at mm-waves in various configurations and a practically acceptable agreement was found. The proposed structures greatly simplify the reconfigurable unit cell testing.
Ahmad G, Underwood C, Brown T, Loh T (2017) Role of Surface Waves in Improving the Reflection Properties of a Millimetre Wave Reflectarray Unit Cell, LAPC 2017 Proceedings The Institution of Engineering and Technology
A steady increasing trend towards millimetre waves (mm-waves) for next generation communication has initiated an intensive research in the field of mm-wave antenna technologies. Reflectarray antennas being one of the potential candidates offer significant advantages over parabolic and phased array antennas at mm-wave bands. In a well-designed reflectarray, the overall performance is mainly determined by its comprising unit cell(s). Most of the recent reflectarray designs are based on printed microstrip technology. It is well known that surface waves get generated in printed microstrip technology and contribute to loss in the radiated signal power in the intended direction. This paper analyses the effect of surface waves in the reflection properties of a printed microstrip millimetre wave reflectarray unit cell. The analytical results are compared with measured data at 32 GHz and an excellent agreement was observed. It was observed that surface waves, though generally considered to have malign effects in antennas, play a significant positive role in the reduction of reflection loss magnitude at unit cell level.
Ahmad Ghulam, Brown Tim W.C., Underwood Craig I., Loh Tian H. (2018) An investigation of millimeter wave reflectarrays for small satellite platforms, Acta Astronautica 151 pp. 475-486 Elsevier
This article reports two contributions related to reflectarray antenna design at millimeter waves (mm-waves). First, a closed form analytical formulation is provided for the prediction of reflection properties of square/rectangular mm-waves reflectarray unit cells based on various quality factors and the theory of waveguide coupled resonators. To ensure a high accuracy at mm-waves, the effects of fringing fields, surface waves, metal conductivity, and metal surface roughness are included in the analysis. This analysis program greatly facilitates the parametric studies of a unit cell's constituting parameters to converge on an optimum design solution. Secondly, the concept of phase quantization is proposed for a cost effective realization of mm-waves reflectarrays. The developed formulation in the first contribution was used to design two 3 bit phase quantized, single layer, 19 wavelength, passive reflectarrays at 60/GHz. The test results are compared with simulations and a very good agreement was observed. These findings are potentially useful for the realization of high gain antennas for mm-wave inter-satellite links in small satellite platforms.
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.
Next generation wireless communication systems are expected to support unprecedented extremely high data transfer rates. This objective requires wider bandwidths which are presently only available at the millimeter waves (mm-waves) spectrum (30-300 GHz). Due to stringent propagation impairments, mm-waves mainly rely on the line of sight communication links which require high gain and wide angle beamsteeering smart antennas to maintain their performance. Owing to the complexity and losses in array beamformers, the realization of a high gain wide angle electronic beamsteering antenna solution at mm-waves becomes a key challenge.

This research provides a potentially competing novel high gain electronic beamsteering antenna solution for mm-waves in the form of a phase quantized smart reflectarray consisting of high performance reconfigurable unit cells. Novel contributions of this research are: (a) Analysis of mm-wave reflectarray unit cells including the effects of fringing fields, surface waves, finite metal conductivity and metal surface roughness. (b) New measurement techniques for mm-wave reflectarray unit cells to ease the alignment, orientation, and DC biasing issues. (c) Characterization of PIN diodes at 10 GHz and 60 GHz for their ON/OFF state models extraction from measurements. (d) Design of three state implicit phase shifter reflectarray unit cell at 60 GHz, reduction in its DC bias lines, and an optimization technique to improve polarization purity of a multi-state reconfigurable unit cell. (e) A fast algorithm to prepare the electromagnetic simulation model of large reflectarrays. (f) Conception and measurement based validation of phase quantized reflecarrays and their performance matrix. (g) Conception and measurement based analytical solution of low DC power consuming smart reflectarrays.
The resulting solution is agile, simple to implement, do not necessarily require multiple RF chains, enables wide angle electronic beamsteering (+-78 degree), is scalable for any gain/frequency requirements, can be made foldable for smaller satellite platforms, is very reliable, and consumes low DC power. This smart reflectarray platform can implement any phase only synthesis technique for radiation pattern control including single/multiple pencil beams, contoured beams, and their scanning over wider angles. Findings of this research would potentially benefit next generation terrestrial/air/space communication systems and radars.

Underwood Craig, Pellegrino S, Lappas VJ, Bridges Christopher, Baker J (2015) Using CubeSat/micro-satellite technology to demonstrate the Autonomous Assembly of a Reconfigurable Space Telescope (AAReST), Acta Astronautica 114 pp. 112-122 PERGAMON-ELSEVIER SCIENCE LTD
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 at 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 micro/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 spacecrafts will be launched as a single ~40 kg micro-satellite package. The spacecraft busses are based on heritage from Surrey's SNAP-1 and STRaND-1 missions (launched in 2000 and 2013 respectively), whilst the optics, imaging sensors and shape adjusting adaptive mirrors (with their associated adjustment mechanisms) are provided by CalTech/JPL. The spacecraft busses provide precise orbit and attitude control, with inter-satellite links and optical navigation to mediate the docking process. The docking system itself is based on the electromagnetic docking system being developed at the Surrey Space Centre (SSC), together with rendezvous sensing technology developed for STRaND-2. 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 two MirrorSat spacecraft undock and re-dock to the core spacecraft in a linear formation to represent a large (but sparse) aperture for high resolution imaging. The imaging of stars is the primary objective, but other celestial and terrestrial targets are being considered. Teams at CalTech and SSC are currently working on the mission planning and development of space hardware. The autonomous rendezvous and docking system is currently under test on a 2D air-bearing table at SSC, and the propulsion and precision attitude control system is currently in development. Launch is planned for 2016. This paper details the mission concept; technology involved and progress to date, focussing on the spacecraft buses.
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.
Lassakeur Abdelmadjid, Underwood Craig (2017) Precision Attitude Determination And Control System of CubeSats by On-Orbit Determination of the Dynamic Magnetic Moment, Proceedings of ESA GNC 2017 pp. 1-11 European Space Agency
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 in the case of CubeSats as, firstly, their small moments of inertia mean that even small disturbance torques, such as those due to a residual magnetic moment, have a significant effect. Secondly, there are hardware limitations in terms of power, weight and size, which make the task more challenging.
Recently, a research programme has been undertaken at Surrey Space Centre, to study the source of the residual magnetic moment in CubeSats, and to characterise 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 minimising 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. The dynamic nature of the disturbances requires an active mitigation strategy. We therefore propose a new technique using a network of magnetometers to dynamically characterize and then compensate the residual magnetic moment in real time. This paper reports on our findings to date.
Underwood Craig, Collins Nathan (2017) Design and Control of a Y-4 Tilt-Rotor VTOL Aerobot for Flight on Mars, Proceedings of the 68th International Astronautical Congress (IAC) International Astronautical Federation (IAF)

Surrey Space Centre has been working on an autonomous fixed-wing all-electric vertical take-off and landing (VTOL) aerobot for the exploration of Mars for several years. The current design is a novel ?Y-4? configured tilt-rotor, comprising two large fixed co-axial lift rotors embedded in a blended wing/body, with a pair of smaller tractor tilt-rotors mounted just forward of the wing. Thus, there are 4 rotors configured in a ?Y? shape.
During take-off and landing, all four rotors operate in the vertical direction, with the bulk of the lifting force being provided by the thrust of the co-axial lift rotors. During transition to horizontal flight, the pair of tilt-rotors rotate to the horizontal position and the co-axial rotors are slowed as the wings begin to provide aerodynamic lift. Once sufficient speed has been built up, these rotors are stopped, and a set of clam-shell doors close to enclose them to provide a smooth lifting surface over the body. Thus, in forward flight, only the pair of tractor tilt-rotors operate, thereby considerably reducing the electrical power demands of the aircraft compared to, for example, a conventional quad-copter or helicopter design.
The baseline mission of the aerobot is to investigate the Isidis Planitia region on Mars over a month long period using optical sensors during flight and a surface science package when landed. During flight operations the aerobot will take off and land vertically, transitioning to and from horizontal flight. The flight time is around an hour, with the flights taking place close to local noon to maximize the power production of the wing/body mounted solar cells.

A nonlinear six degree of freedom (6DoF) dynamic model incorporating aerodynamic models of the aerobot?s body and rotors has been developed to model the vertical, transition, and horizontal phases of flight. A nonlinear State-Dependent Riccati Equation (SDRE) controller has been developed for each of these flight phases. The nonlinear dynamic model was transformed into a pseudo-linear form based on the states and implemented in the SDRE controller. During transition flight the aerobot is over actuated and the weighted least squares (WLS) method is used for allocation of control effectors. Simulations of the aerobot flying in different configurations were performed to verify the performance of the SDRE controllers, including hover, transition, horizontal flight, altitude changes, and landing scenarios. Results from the simulations show the SDRE controller is a viable option for controlling this novel Martian Aerobot.

Underwood Craig, Cherniakov Mike, Antoniou Michael, Gashinova Marina, Stove Andrew, Hristov Stanislav, Atkinson George, Kuschel Heiner, Wojaczek Philipp, Cristallini Diego (2017) PASSAT: Passive Imaging Radar Constellation for Near-Persistent Earth Observation, Proceedings of the 68th International Astronautical Congress (IAC) International Astronautical Federation (IAF)
Persistent monitoring of large areas using spaceborne Synthetic Aperture Radar (SAR) is a challenging problem for various defence and civil applications. Despite the fact that spaceborne SAR from low Earth orbit (LEO) is a well-developed technology, in practice it cannot provide persistent monitoring of any particular geographical region, as any single satellite has a rather long revisit time. Geostationary Earth Orbit (GEO) SAR missions have been proposed, but here there are major engineering issues due the severe path loss across the distances involved. Indeed, path loss is even more severe in radar systems than it is in radio communications. To provide persistent (or near persistent) monitoring from LEO, a very large number of satellites (~100) would be required to detect short-lived events. However, even though such a solution may be technically possible, a satellite constellation development of this scale may not be economically viable. The PASSAT project was proposed and undertaken by the University of Birmingham, under the sponsorship of the UK Defence Science and Technology Laboratory, to analyse the concept of a fully passive (receive only) spaceborne SAR system based on a constellation of microsatellites. By making use of terrestrial transmitters (we propose to use ground-based broadcasting systems, i.e. DVB-T, DAB, FM radio and similar as transmitters of opportunity), the problem of having to carry a high power pulsed radar transmitter on a microsatellite is eliminated. Instead, the satellite only need carry a suitable receiver, antenna and signal storage facility. It is expected that such a system will: (i) provide imaging of a monitored area with a potentially achievable resolution of 2-3 m in either direction; (ii) cover mainly populated parts of the Earth and, partly, littoral waters; (iii) its costs will be orders of magnitude less in comparison to an equivalent active spaceborne SAR constellation. In addition we may expect more information-rich images, as we are dealing with a multi-static, multi-frequency (VHF/UHF) system which effectively has no equivalent at present. In this paper, the emphasis is on the PASSAT concept, the space segment investigation and the experimental results of passive SAR imaging with DVB-T transmissions undertaken at the University of Birmingham using a local DVB-T transmitter.
Underwood Craig, Lamb D, Irvine S, Dyer Alexander, Duke Richard, Stewart Brian, Taylor Benjamin, Massimiani C, Fellowes S, Baker M (2017) Development and Testing of New Thin-Film Solar Cell (TFSC) Technology: Flight Results from the AlSAT-1N TFSC Payload, Proceedings of the 68th International Astronautical Congress (IAC) International Astronautical Federation (IAF)
The increasing power demands of spacecraft payloads, and the future prospect of space based solar photovoltaic (PV) power stations, mean that there is an emerging requirement for large area solar arrays that will provide far greater power (kWpeak) than is currently available. To be practical, such arrays will need to use solar cells which have a much higher specific power (i.e. power per unit mass) and a much lower cost per watt than current space-rated solar PV technologies. To this end, the Centre for Solar Energy Research (CSER) at Swansea University, the Surrey Space Centre (SSC) and the Department for Mechanical Sciences at the University of Surrey, have been working on a new solar cell technology, based on thin film cadmium telluride (CdTe), deposited directly onto ultra-thin space qualified cover glass. This offers a potentially high specific power, low-cost technology with the added benefit of allowing a high degree of solar array flexibility for improved stowage volume and novel deployment strategies. Cells based on this innovative solar cell architecture have been manufactured and tested under a three year UK Engineering and Physical Science Research Council (EPSRC) funded project, with the result that highly efficient (for their class) cells were produced, which passed mechanical, thermal and ionising radiation tests with great success. Whilst this work was in progress, an opportunity to fly test cells on the joint Algerian Space Agency ? UK Space Agency AlSat-1N Technology Demonstration CubeSat arose, and a successful bid was made to fly a payload capable of characterising the cells in orbit, via an automatic Current-Voltage (I-V) measurement circuit. The resulting Thin Film Solar Cell (TFSC) payload, comprising four test cells, was integrated onto AlSat-1N at Surrey, and launched from India into a 661 km × 700 km, 98.20° Sun Synchronous orbit on 26th September 2016. This paper describes the new cell technology, the pre-flight ground testing, the flight payload, and the first flight results of thin film CdTe solar cells flying on an international 3U CubeSat technology demonstrator.
Keywords: (Thin-Film Solar Cells, CubeSat, Technology Demonstration)
Cornogolub Alexandru, Underwood Craig, Voigt Philipp (2017) Design of a Rigid Boom Electro Dynamic/ Drag-Sail (RBEDDS) Hybrid Deorbiting System, Proceedings of the 68th International Astronautical Congress (IAC) International Astronautical Federation (IAF)

The measured and projected growth of space debris makes it clear that technology for the removal of spacecraft at the end-of-life is an absolute necessity if we are to prevent the Kessler syndrome of catastrophic collisional cascading.

Electro-dynamic tethers (EDTs) have been proposed as an effective means of deorbiting spacecraft ? particularly from low Earth orbit (LEO). Such systems rely on the Lorentz force developed by a long conductive tether cutting through the Earth?s magnetic field due to the host spacecraft?s orbital motion. The electro-motive force generated drives a current through the tether, which is returned through the local space plasma by some form of active or passive plasma-contacting electrode. This removes (or adds) energy from the spacecraft?s motion, causing it to lose (or gain) altitude. As such, EDTs have the advantage of been self-powered, and propellantless, however, to be effective, the tethers typically have to be several km long, and be very thin to save mass. They are therefore flexible and derive their stability through the gravity gradient effect. This leads to such systems being most effective in low-Earth equatorial orbits, and unfortunately, much less effective in near polar orbits (e.g. Sun-synchronous orbit) or for orbits beyond LEO.

To this end, we have developed a novel concept for an uncontrolled removal system based on electro dynamical principles. Instead of a long flexible tether (which have proven problematic to deploy), we propose the use of long (~150m-300m) rigid electro-dynamic booms in a ?bar? or ?cross? formation, actively powered, and coated with an electron emissive material. The main advantage of such a structure is that, for satellites in polar orbits, it leads to a larger Lorentz force. Also, the deployment is more reliable and the attitude control is greatly simplified (compared to the use of a flexible tether). To complete the circuit, electrons will be passively collected by a conductive deployable ?sail?, which will also act as a drag sail at low altitudes. A ground demonstrator is under development based around a 6U CubeSat structure, which could form the basis for a later in-orbit demonstrator.
This work is conducted as a part of the European Commission funded Horizon-2020 TeSeR (Technology for Self-Removal) project, which aims to demonstrate the feasibility of a scalable post mission removal system which should be able to be connected to different satellites via a standard interface.

Underwood Craig, Viquerat A, Taylor Benjamin, Massimiani Chiara, Duke Richard, Fellowes S, Schenk M, Stewart Brian, Bridges C P, Masutti D, Denis A (2018) The InflateSail CubeSat Mission ? The First European Demonstration of Drag-Sail De-Orbiting, AAS Advances in the Astronautical Sciences Series 163 Univelt, Inc., USA
The InflateSail (QB50-UK06) CubeSat, designed and built at the Surrey Space Centre (SSC) at the University of Surrey, UK, for the Von Karman Institute (VKI), Belgium ? was one of the technology demonstrators for the QB50 pro-gramme. The 3.2 kilogram 3U CubeSat was equipped with a 1 metre long inflat-able boom and a 10m2 deployable drag 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 simultane-ously on the PSLV (polar satellite launch vehicle) C-38 from Sriharikota, India on 23rd June 2017 into a 505km, 97.44o Sun-synchronous orbit (SSO). Shortly after orbital insertion, InflateSail booted-up, and, once safely clear of the other satellites on the launch, it automatically activated its payload ? firstly, deploying a 1 metre long inflatable boom comprising a metal-polymer laminate tube, using a cool gas generator (CGG) to provide the inflation gas, and secondly, using a brushless DC motor at the end of the boom to extend four lightweight bistable rigid composite (BRC) booms to draw out the 3.1m x 3.1m square, 12 micron thick polymer drag-sail. As intended, the satellite immediately began to lose alti-tude, and re-entered the atmosphere just 72 days later ? thus demonstrating for the first time the de-orbiting of a spacecraft using European inflatable and drag-sail technologies. The boom/drag-sail technology developed by SSC will next be used on the RemoveDebris mission, due for launch in 2018, which will demon-strate the capturing and de-orbiting of artificial space debris targets using a net and harpoon system.
Lassakeur Abdelmadjid, Underwood Craig, Taylor Benjamin (2018) Enhanced Attitude Stability and Control for CubeSats by Real-Time On-Orbit Determination of Their Dynamic Magnetic Moment, 69th International Astronautical Congress International Astronautical Congress
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 in the case of CubeSats, mainly because their small moment of inertia means that even small disturbance torques, such as those due to a residual magnetic moment, have a significant effect. In addition, hardware limitations in terms of power, weight and size, 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 analysis indicates this is often due to un-modelled magnetic moments mainly caused by the current flowing in the spacecraft. Some CubeSats also carry permanent magnets. However, by contrast, the other typical attitude disturbance sources for spacecraft (gravity gradient, aerodynamic, and solar radiation pressure torques) decreases significantly when the satellites become small. Recently, a research programme has been undertaken at Surrey Space Centre at the University of Surrey, to study the source of the residual magnetic field in CubeSats, and to characterise 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 minimising current-loop areas, and minimising the use of permeable materials, these disturbances can still be an issue when a high degree of stability is required. The dynamic nature of the disturbances requires an active mitigation strategy. We therefore propose a new technique using a network of magnetometers to dynamically characterize and then compensate the calculated residual magnetic moment ? in flight and in real time. This can be done by implementing a network of eight miniature 3-axis magnetometers on the spacecraft, with an additional one mounted on a deployable boom. These are used to determine the strength and the centre of the magnetic dipole of the spacecraft dynamically. The information will be used by the Attitude Determination and Control System (ADCS) control loops to compensate the measured residual magnetic moment. This technique will contribute to achieving more precise pointing, agility and stability of CubeSats. A hardware prototype using eight HMC1053 3-axis magnetometers monitored and controlled via a Raspberry Pi, was developed and successfully tested with the engineering model of the Alsat-1N CubeSat in a Helmholtz Coil arrangement at the Surrey Space Centre. This demonstrated the real-time dynamic measurement aspect of the technique proposed in this paper. This paper reports on our findings to date.
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 (2018) InflateSail De-Orbit Flight Demonstration Results and Follow-On Drag-Sail Applications, 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
deployable drag
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
Sun-synchronous orbit.
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.
Lassakeur Abdelmadjid, Underwood Craig, Taylor Benjamin (2018) Enhanced Attitude Stability and Control for CubeSats by Real-Time On-Orbit Determination of Their Dynamic Magnetic Moment, Proceedings of the 69th International Astronautical Congress (IAC) International Astronautical Federation (IAF)
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 in the case of CubeSats,
mainly because their small moment of inertia means that even small disturbance torques, such as those due to a
residual magnetic moment, have a significant effect. In addition, hardware limitations in terms of power, weight and
size, 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 analysis indicates this is often due to un-modelled
magnetic moments mainly caused by the current flowing in the spacecraft. Some CubeSats also carry permanent
magnets. However, by contrast, the other typical attitude disturbance sources for spacecraft (gravity gradient,
aerodynamic, and solar radiation pressure torques) decreases significantly when the satellites become small.
Recently, a research programme has been undertaken at Surrey Space Centre at the University of Surrey, to study the
source of the residual magnetic field in CubeSats, and to characterise 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 minimising current-loop areas, and minimising the use of permeable materials, these
disturbances can still be an issue when a high degree of stability is required. The dynamic nature of the disturbances
requires an active mitigation strategy. We therefore propose a new technique using a network of magnetometers to
dynamically characterize and then compensate the calculated residual magnetic moment ? in flight and in real time.
This can be done by implementing a network of eight miniature 3-axis magnetometers on the spacecraft, with an
additional one mounted on a deployable boom. These are used to determine the strength and the centre of the
magnetic dipole of the spacecraft dynamically. The information will be used by the Attitude Determination and
Control System (ADCS) control loops to compensate the measured residual magnetic moment. This technique will
contribute to achieving more precise pointing, agility and stability of CubeSats. A hardware prototype using eight
HMC1053 3-axis magnetometers monitored and controlled via a Raspberry Pi, was developed and successfully
tested with the engineering model of the Alsat-1N CubeSat in a Helmholtz Coil arrangement at the Surrey Space
Centre. This demonstrated the real-time dynamic measurement aspect of the technique proposed in this paper. This
paper reports on our findings to date.
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, Atkinson George, Sayin Alp, Cherniakov Mike, Antoniou Michail, Dyer Alex (2018) PASSAT: Passive Bi-Static Radar Imaging Constellation ? Airborne Trials and In-Orbit Demonstrator Design, Proceedings of the 69th International Astronautical Congress (IAC) International Astronautical Federation (IAF)
Persistent monitoring of large areas using spaceborne Synthetic Aperture Radar (SAR) is a challenging problem for
various defence and civil applications. Despite the fact that spaceborne SAR from low Earth orbit (LEO) is a welldeveloped
technology, in practice it cannot provide persistent monitoring of any particular geographical region, as
any single satellite has a rather long revisit time. Geostationary Earth Orbit (GEO) SAR missions have been
proposed, but here there are major engineering issues due the severe path loss across the distances involved. Indeed,
path loss is even more severe in radar systems than it is in radio communications. To provide persistent (or near
persistent) monitoring from LEO, a very large number of satellites (~100) would be required to detect short-lived
events. However, even though such a solution may be technically possible, a satellite constellation development of
this scale may not be economically viable. The PASSAT project was proposed and undertaken by the University of
Birmingham, under the sponsorship of the UK Defence Science and Technology Laboratory, to analyse the concept
of a fully passive (receive only) spaceborne SAR system based on a constellation of microsatellites. By making use
of terrestrial transmitters (we propose to use ground-based broadcasting systems, i.e. DVB-T, DAB, FM radio and
similar as transmitters of opportunity), the problem of having to carry a high power pulsed radar transmitter on a
microsatellite is eliminated. Instead, the satellite only need carry a suitable receiver, antenna and signal storage
facility. It is expected that such a system will: (i) provide imaging of a monitored area with a potentially achievable
resolution of 2-3 m in either direction; (ii) cover mainly populated parts of the Earth and, partly, littoral waters; (iii)
its costs will be orders of magnitude less in comparison to an equivalent active spaceborne SAR constellation. In
addition we may expect more information-rich images, as we are dealing with a multi-static, multi-frequency
(VHF/UHF) system which effectively has no equivalent at present.
In this paper, we report the results of a series of ground-based and airborne trials of the system, around Birmingham,
Coventry and Bruntingthorpe Airfield, which make use of DVB-T transmissions from the Sutton Coldfield
transmitter at ranges up to 46km. In the processed images, roads, wind turbines, hedgerows and trees are all clearly
identified. We also discuss a proposed spaceborne demonstrator, based on a 12U CubeSat platform with a deployable
high-gain UHF helical antenna
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
sensors.
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.
Atkinson George, Sayin Alp, Stove Andrew, Underwood Craig, Cherniakov Mikhail, Antoniou Michael (2018) Passive SAR Satellite System (PASSAT): airborne demonstrator and first results, IET Radar, Sonar & Navigation Institution of Engineering and Technology
This paper presents the development and execution of an airborne experimental campaign as part of the continuing investigation of a passive Synthetic Aperture Radar using digital television broadcasting stations as illuminators of opportunity, and micro-/nano-satellite receivers in Low Earth Orbit. For the flight experiments, a hardware demonstrator was developed that utilised two receiving antennas, allowing both cross-correlation and auto-correlation range compression schemes, and was mounted to an airborne platform to image stationary rural areas up to 50 km from the transmitter. This paper presents the first image results of these experiments as well as initial analysis of image formation aspects including, range compression scheme and effects on the image quality of the signal to noise on the reference channel.
Voigt Philipp, Vogt Cornelius, Schubert Ralf, Stokes Hedley, Underwood Craig, Cornogolub Alexandru, Macdonald Malcolm, Kerr Emma, Smith Lesley Jane, Förstner Roger, Wander Alexandra, Konstantinidis Kostas, Valli Monica, Brilli Simone, Lips Tobias, León Pérez Laura, Ghizoni Leonardo, Kristensen Anders, Dalsgaard Nielsen Jens Frederik, McInnes Colin, Bensoussan Denis (2018) TeSeR ? Technology for Self-Removal ? Status of a Horizon 2020 project to ensure the Post-Mission-Disposal of any future spacecraft, Proceedings of the 69th International Astronautical Congress (IAC) International Astronautical Federation (IAF)
One major source of new space debris are spacecraft (S/C) that are not removed from orbit after the end of their
operational lifetime. Many regulations (e.g. ISO 24113) require the removal of S/C at the end of operation - known
as Post-Mission-Disposal (PMD) - with a compliance rate of 90% to ensure that S/C do not become a new source of
space debris. An analysis performed by ESA shows that the success rate of PMD in 2013 was in the range of about
50%-60%.
The goal of TeSeR (Technology for Self-Removal) is to take the first step towards the development of a costefficient,
but highly reliable PMD module. This PMD module is to be attached to the S/C on ground and it shall
ensure the PMD of the S/C at the end of the operational lifetime. This PMD module shall be scalable and flexible,
thus, enabling the PMD of any future S/C in an Earth orbit. Ultimately, the gap between the required 90% PMD
success rate and the current success rate can be closed.
The technological enhancements and developments required for successful PMD are addressed and analysed in
TeSeR. The project?s primary aims are
· to develop, manufacture and test an on-ground prototype of the PMD module,
· to develop three different removal subsystems (solid propulsion, electro-dynamical systems and
deployable structures) for easy plug-in/plug-out implementation to the PMD module.
This is the first step to demonstrate the main aspects of such a PMD module and the required main technologies.
The technical activities are supported by non-technical tasks, e.g. investigation of legal issues relating to a PMD
module, execution of a market study and consideration of this technology as a leverage to advance ISO norms. This
double tracked approach ensures that the technological developments are embedded into the needs of the space
community right from the start.
Up to now the prototypes of the three removal subsystems have been developed, manufactured and tested with a
common interface for implementation into the PMD module prototype. The PMD module prototype will be
manufactured until summer 2018. Afterwards the removal subsystems will be integrated via the same interface.
Airbus is the coordinator (and potential launch customer) of TeSeR. The project is conducted together with 10
notable institutes and companies from all across Europe with experts who have been working in the space debris
issue for many years.
Cannon Paul, Angling Matthew, Barclay Les, Curry Charles, Dyer Clive, Edwards Robert, Greene Graham, Hapgood Michael, Horne Richard, Jackson David, Mitchell Cathryn, Owen John, Richards Andrew, Rogers Christopher, Ryden Keith, Saunders Simon, Sweeting Martin, Tanner Rick, Thomson Alan, Underwood Craig (2013) Extreme space weather: impacts on engineered systems and infrastructure, In: Space Weather - full report Royal Academy of Engineering
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.