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 C, Evans HDR, Ryden K, 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
Underwood C, Pellegrino S, Lappas VJ, Bridges CP, 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
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 KA, Morris PA, Ford KA, Hands ADP, Dyer CS, Taylor B, Underwood CI, 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 CI, Pellegrino S, Lappas V, Bridges CP, Taylor BO, Chhaniyara S, Theodorou T, Shaw P, Arya M, Breckinridge J, Hogstrom K, Patterson K, Steeves J, Wilson L, Horri N (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-INST ELECTRICAL ELECTRONICS ENGINEERS INC
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 &
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 D, Underwood C, Barrioz V, Gwilliam R, Hall J, Baker M, Irvine S (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 D, Underwood C, Barrioz V, Gwilliam R, Hall J, Baker M, Irvine S (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.