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 XI6362 SPIE-INT SOC OPTICAL ENGINEERING
Shimizu T, Underwood C (2013) Super-capacitor energy storage for micro-satellites: Feasibility and potential mission applications, ACTA ASTRONAUTICA85pp. 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 & STRUCTURES84(5-6)pp. 340-350 PERGAMON-ELSEVIER SCIENCE LTD
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 Photovoltaics6(2)pp. 557-561
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 SCIENCE54(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.
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 SCIENCE36(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.
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 M51(4)pp. 40-56 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Modern small satellites (MSS) are revolutionizing the space industry. They can drastically reduce the mission cost, and can make access to space more affordable. The relationship between a modern small satellite and a "conventional" large satellite is similar to that between a modern compact laptop and a "conventional" work-station computer. This paper gives an overview of antenna technologies for applications in modern small satellites. First, an introduction to modern small satellites and their structures is presented. This is followed by a description of technical challenges in the antenna designs for modern small satellites, and the interactions between the antenna and modern small satellites. Specific antennas developed for modern small-satellite applications are then explained and discussed. The future development and a conclusion are presented.
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 LETTERS10pp. 987-990 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Zhao W, Underwood C (2014) Robust transition control of a Martian coaxial tiltrotor aerobot, ACTA ASTRONAUTICA99pp. 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 CONTRIBUTIONSpp. 101-109 SPRINGER
Taylor B, Underwood C, Evans HDR, Daly E, Ryden KA, Santin G (2008) Galileo GIOVE-A MEORAD Results and Analysis, IEEE TRANSACTIONS ON NUCLEAR SCIENCE55(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 OBSERVATIONpp. 311-320 SPRINGER-VERLAG BERLIN
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 2013pp. 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.
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-III134pp. 173-183 UNIVELT INC
Song H, Underwood C (2007) A Mars VTOL aerobot - Preliminary design, dynamics and control, 2007 IEEE AEROSPACE CONFERENCE, VOLS 1-9pp. 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 GENERATION9(5)pp. 420-423
INST ENGINEERING TECHNOLOGY-IET
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 SCIENCE56(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 XII6745pp. 74503-74503 SPIE-INT SOC OPTICAL ENGINEERING
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.
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.
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
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.
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.
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).
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.
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.
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.
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.
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
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.
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.
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.
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 20149
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 Satellitespp. 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.
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.
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)
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 Series163
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.
Underwood Craig, Viquerat Andrew, Schenk Mark, Taylor Ben, Massimiani Chiara, Duke Richard, Stewart Brian, Fellowes Simon, Bridges Chris, Aglietti Guglielmo, Sanders Berry, Masutti Davide, Denis Amandine (2019) InflateSail De-Orbit Flight Demonstration Results and Follow-On Drag-Sail Applications,Acta Astronautica - Proceedings of the 69th International Astronautical Congress (IAC)
International Astronautical Federation (IAF)
The InflateSail (QB50-UK06) CubeSat, designed and built at the Surrey Space Centre (SSC) for the Von Karman
Institute (VKI), Belgium, was one of the technology demonstrators for the European Commission?s QB50
programme. The 3.2 kg 3U CubeSat was equipped with a 1 metre long inflatable mast and a 10m2
sail. InflateSail's primary mission was to demonstrate the effectiveness of using a drag sail in Low Earth Orbit (LEO)
to dramatically increase the rate at which satellites lose altitude and re-enter the Earth's atmosphere and it was one of
31 satellites that were launched simultaneously on the PSLV (polar satellite launch vehicle) C-38 from Sriharikota,
India on 23rd June 2017 into a 505km, 97.44o
Shortly after safe deployment in orbit, InflateSail automatically activated its payload. Firstly, it inflated its metrelong
metal-polymer laminate tubular mast, and then activated a stepper motor to extend four lightweight bi-stable
rigid composite (BRC) booms from the end of the mast, so as to draw out the 3.1m x 3.1m square, 12mm thick
polyethylene naphthalate (PEN) drag-sail. As intended, the satellite immediately began to lose altitude, causing it to
re-enter the atmosphere just 72 days later ? thus successfully demonstrating for the first time the de-orbiting of a
spacecraft using European inflatable and drag-sail technologies.
The InflateSail project was funded by two European Commission Framework Program Seven (FP7) projects:
DEPLOYTECH and QB50. DEPLOYTECH had eight European partners including DLR, Airbus France, RolaTube,
Cambridge University, and was assisted by NASA Marshall Space Flight Center. DEPLOYTECH?s objectives were
to advance the technological capabilities of three different space deployable technologies by qualifying their
concepts for space use. QB50 was a programme, led by VKI, for launching a network of 50 CubeSats built mainly by
university teams all over the world to perform first-class science in the largely unexplored lower thermosphere.
The boom/drag-sail technology developed by SSC will next be used on a third FP7 Project: RemoveDebris,
launched in 2018, which will demonstrate the capturing and de-orbiting of artificial space debris targets using a net
and harpoon system. This paper describes the results of the InflateSail mission, including the observed effects of
atmospheric density and solar activity on its trajectory and body dynamics. It also describes the application of the
technology to RemoveDebris and its potential as a commercial de-orbiting add-on package for future space missions.
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.
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
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.
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
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.
Most satellites, currently in use, don't incorporate any post mission disposal system and therefore will end up as debris once they reach the end of their life. Without any intervention, these objects could endanger future space missions, once their density is high enough. In this paper the authors propose a new concept for an uncontrolled removal system based on electro dynamical principles. Instead of long flexible tethers (which have proven problematic to deploy), we consider using relatively short (~150m-300m) rigid electro-dynamic booms. 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 (because the booms are rigid). A ground demonstrator is under development based around a 6U CubeSat structure. We also look at different techniques which could be used for electron emission into the surrounding plasma because currently this is what limits the generated currents in the proposed system. 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.
Space telescopes are our ?eyes in the sky? that enable unprecedented
astronomy missions and also permit Earth
observation integral to science and national security. On
account of the increased spatial resolution, spectral coverage,
and signal-to-noise ratio, there is a constant clamour
for larger aperture telescopes by the science and surveillance
communities. This paper addresses a 25 m modular
telescope operating in the visible wavelengths of the electromagnetic
spectrum; such a telescope located at geostationary
Earth orbit would permit 1 m spatial resolution of
a location on Earth. Specifically, it discusses the requirements
and architectural options for a robotic assembly
system, called Robotic Agent for Space Telescope Assembly
(RASTA). Aspects of a first-order design and initial
laboratory test-bed developments are also presented.
Earth Observation via satellite has been successfully used for several decades in many applications. Monitoring climate change is the most challenging one, as it requires highly accurate data to enable detection of small changes in naturally variable signals over different spatial and temporal scales. A measure used in metrology to assess the quality of the data is measurement uncertainty. However, to date, many satellite products still do not have uncertainties, the accuracy requirements are not defined precisely and even calibrations are performed without associated measurement uncertainty budgets. Thus is it often impossible to put an unbiased quality mark to the data that, by default, requires the highest levels of accuracy. This poses the risks of using poor quality data as the input to climate change models.
This research focuses on the \ground truth" measurement methodology called vicarious calibration. This is an independent post-launch satellite calibration technique based on a comparison of satellite readings with ground data and atmospheric modelling. Two test sites were selected as examples, land and ocean, to have uncertainty evaluated for their ground products following the Guide to the Expression of Uncertainty in Measurement (GUM) methodology.
A new radiometric calibration site, Gobabeb in the Namib Desert, was established for radiometric calibration of Top-of-Atmosphere (TOA) radiance/reflectance level 1 (L1) satellite products, and a campaign was conducted to measure the ground's reflectance. All instruments used during the initial characterisation were previously calibrated and characterised in optical laboratories. The in situ uncertainty budget was evaluated and validated by the comparison of the results to an alternative measurement source. The primary input of this research to the scientific community, apart from the new site, is a revised SI traceability chain for the ground reflectance field measurements. Hitherto, the reflectance reference standards used in situ had a calibration that did not match field illumination conditions. Although this problem was known, often it was not addressed or dealt with accurately. This study proposed a new field calibration value for the reflectance standard that combines direct and diffuse components weighted accordingly to the wavelength and atmospheric conditions during the measurement.
The work on the ocean site concentrated on the existing Boueé pour l?acquisition de Séries Optiques á Long Terme (BOUSSOLE) site that is permanently deployed in the Ligurian Sea and provides Bottom of Atmosphere (BOA) water leaving radiance/reflectance level 2 (L2) Ocean Colour System Vicarious Calibration (SVC). This site had a preliminary uncertainty estimated as one generic number for all spectral channels and environmental conditions. A new uncertainty budget was developed by a detailed evaluation of each identified uncertainty component and these were combined by applying the Monte Carlo Method (MCM). As a result, a dynamic uncertainty evaluation for each measurement and the spectral band was produced addressing real measurement conditions and their effects on the quality of the relevant in situ products.
Gorroño Javier, Hunt Samuel, Scanlon Tracy, Banks Andrew, Fox Nigel, Woolliams Emma, Underwood Craig, Gascon Ferran, Peters Marco, Fomferra Norman, Govaerts Yves, Lamquin Nicolas, Bruniquel Veronique (2018) Providing uncertainty estimates of the Sentinel-2 top-of-atmosphere measurements for radiometric validation activities,European Journal of Remote Sensing51(1)pp. 650-666
Taylor & Francis
As part of the Sentinel-2 mission, a Radiometric Uncertainty Tool (RUT) has been recently released to the community. This tool estimates the Sentinel-2 radiometric uncertainty associated with each pixel in the top-of-atmosphere (TOA) reflectance factor images provided by the European Space Agency (ESA). The use of such information enables users to assess the ?fitness for purpose? of the data to their specific application. The work described here summarises the efforts and results of integrating the RUT for radiometric validation activities
for the Sentinel-2 mission. Starting from the results provided by the RUT, the focus will be on providing a methodology to calculate the uncertainty associated with the mean TOA reflectance factor in a Region of Interest (ROI). Two different methods ? one simple method directly using the RUT and a more rigorous one based on Monte Carlo method (MCM) propagation ? are proposed and compared. These two methods focus on the effect of the spectral, spatial and temporal correlation of the errors in different ROI pixels and the impact of correlation on the uncertainty associated with the mean TOA reflectance factor. The study has also considered the impact of uncertainty contributions not included in the first version of the RUT.
Climate change is of increasing concern and efforts to mitigate its effects are targeted on reducing fossil CO2 emissions. Satellite observations play a key role in the understanding and management of the problem. Whilst detecting CO2 optically is relatively straight-forward, and has been achieved with small satellites, accurate quantitative mapping of CO2 requires very high precision (<1%) measurements of gas concentration. This is usually achieved through identifying CO2 by its spectral absorption bands at 1.56-1.62¼m and 1.92-2.06¼m wavelength by using high resolution spectrometers (e.g. 0.27cm-1 resolution at a signal-to-noise ratio (SNR) of >300:1). This normally requires high performance, large and complex instruments whose high cost, mass, volume, and power requirements preclude their use on small satellites. This paper presents the developmental stage of a single channel (1.6 ¼m) compact precision Spatial Heterodyne Atmospheric Carbon-Dioxide Spectrometer (SHACS), which utilises the Spatial Heterodyne Spectrometer (SHS) technique to form a robust, compact, no-moving-part Fourier Transform Spectrometer (FTS). This instrument achieves a high spectral resolution of 0.25cm-1 at a high SNR of >700:1 and can fit into a micro-satellite platform. With this performance, high quality measurements of atmospheric CO2 concentration with measurement precision of <4 ppm can be achieved.
Presented here is CHAFF (CubeSat Hyperspectral Application For Farming), a design concept for a CubeSat-based Hyperspectral Imager (CHSI) intended to supply high quality hyperspectral image data cubes to the agricultural community. CHAFF has been designed holistically as a system, considering all design and operational characteristics of a CHSI instrument and platform together: including the re-stricted payload mass and volume associated with CubeSats, the platform pointing stability/accuracy limitations, and the restricted downlink data budget. To this end, CHAFF will employ optically aided geometric co-registration methods, which will allow on-board construction of the hyperspectral data cube. This allows the use of powerful lossless data compression schemes to mitigate the downlink data budget limitations. In addition, a calibration methodology using a tuneable laser source at NPL, will be employed pre-flight to achieve rapid and accurate spectral and radiometric calibration, essential for the production of science-grade data sets from the proposed CubeSat constellations. A benchtop prototype has been constructed and a promising spectral resolution of 3nm at around 625nm has been achieved. In addition the auxiliary imager for the optically-aided geometric co-registration has been demonstrated.
Persistent monitoring of large areas using spaceborne Synthetic Aperture Radar (SAR) is a challenging problem for various defence and civil applications. 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 CubeSats. By making use of terrestrial transmitters (e.g. Digital Video Broadcasting ? Terrestrial (DVB-T) or similar transmitters of opportunity), the problem of having to carry a high power pulsed radar transmitter on the satellite is eliminated. Instead, the satellite only need carry a suitable receiver, antenna and signal storage facility. It is expected that such a system would provide imaging of populated areas with a potential resolution of ~2-3 m. In this paper, we describe progress towards the design of such a system, including the results of a series of ground-based and airborne trials which make use of DVB-T transmissions from the Sutton Coldfield transmitter. In the processed images, roads, wind turbines, electricity pylons, hedgerows and trees are all clearly identified.
The InflateSail (QB50-UK06) CubeSat, designed and built at the Surrey Space Centre (SSC) for the Von Karman Institute (VKI), Belgium, was a technology demonstrator built under the European Commission?s QB50 programme. The 3.2 kilogram 3U CubeSat was equipped with a 1 metre long inflatable mast and a 10m2 deployable drag sail and was one of 31 satellites that were launched simultaneously on the PSLV (polar satellite launch vehicle) C-38 from Sriharikota, India on 23rd June 2017 into a 505km, 97.44o Sun-synchronous orbit. Shortly after insertion into orbit, InflateSail automatically activated its drag-sail payload, and, as planned, began to lose altitude, causing it to re-enter the atmosphere just 72 days later ? successfully demonstrating for the first time the de-orbiting of a spacecraft using European inflatable and drag-sail technologies. This paper discusses the dynamics we observed during the descent, including the sensitivity of the craft to atmospheric density changes. The InflateSail project was funded by two European Commission Framework Program Seven (FP7) projects: DEPLOYTECH and QB50. QB50 was a programme, led by VKI, for launching a network of 50 CubeSats built mainly by university teams all over the world to perform first-class science in the largely unexplored lower thermosphere.
Curiel Alex da Silva, Whittaker Phil, Bird Rachel, Haslehurst Andrew, Nejadi Pejman, Victoria Irwin, Cawthorne Andrew, Underwood Craig, Sweeting Martin (2019) Synthetic Aperture Radar on a Nanosatellite - is it Possible?,Proceedings of the 12th IAA Symposium on Small Satellites for Earth Observation
International Academy of Astronautics (IAA)
The implementation of a viable Synthetic Aperture Radar (SAR) mission using small satellites
faces significant technological and financial challenges, and this paper evaluates how small such a spacecraft
could be made whilst still fulfilling a useful mission. SAR offers a range of complementary capabilities
alongside other Earth Observation systems with various unique features, but developing such spacecraft
has traditionally been expensive and technologically challenging. It is only in the most recent years
that small satellite SAR missions have been implemented and operated, and this paper examines the state
of the art and the challenges. Furthermore the opportunities of how small SAR satellites can help realise
new Earth Observation capabilities not available on existing traditional SAR satellites are described using
examples of missions under development or reference design missions.
Nanjangud Angadh, Underwood Craig I., Bridges Christopher P., Saaj Chakravarthini M., Eckersley Steve, Sweeting Martin, Biancod Paolo (2019) Towards Robotic On-Orbit Assembly of Large Space Telescopes: Mission Architectures, Concepts, and Analyses,Proceedings of the International Astronautical Congress, IACpp. 1-25
International Astronautical Federation
Over the next two decades, unprecedented astronomy missions could be enabled by space telescopes larger than the
James Webb Space Telescope. Commercially, large aperture space-based imaging systems will enable a new generation
of Earth Observation missions for both science and surveillance programs. However, launching and operating
such large telescopes in the extreme space environment poses practical challenges. One of the key design challenges
is that very large mirrors (i.e. apertures larger than 3m) cannot be monolithically manufactured and, instead, a segmented
design must be utilized to achieve primary mirror sizes of up to 100m. Even if such large primary mirrors
could be made, it is impossible to stow them in the fairings of current and planned launch vehicles, e.g., SpaceX?s
Starship reportedly has a 9m fairing diameter. Though deployment of a segmented telescope via a folded-wing design
(as done with the James Webb Space Telescope) is one approach to overcoming this volumetric challenge, it is considered
unfeasible for large apertures such as the 25m telescope considered in this study. Parallel studies conducted
by NASA indicate that robotic on-orbit assembly (OOA) of these observatories offers the possibility, surprisingly,
of reduced cost and risk for smaller telescopes rather than deploying them from single launch vehicles but this is
not proven. Thus, OOA of large aperture astronomical and Earth Observation telescopes is of particular interest to
various space agencies and commercial entities. In a new partnership with Surrey Satellite Technology Limited and
Airbus Defence and Space, the Surrey Space Centre is developing the capability for autonomous robotic OOA of large
aperture segmented telescopes. This paper presents the concept of operation and mission analysis for OOA of a 25m
aperture telescope operating in the visible waveband of the electromagnetic spectrum; telescopes of this size will be
of much value as it would permit 1m spatial resolution of a location on Earth from geostationary orbit. Further, the
conceptual evaluation of robotically assembling 2m and 5m telescopes will be addressed; these missions are envisaged
as essential technology demonstration precursors to the 25m imaging system.
CubeSats are being increasingly specified for demanding Earth observation and astronomical applications where precise pointing, agility, and stability are critical requirements. Such precision is difficult to achieve in the case of CubeSats, mainly because of their small moment of inertia, means that even small disturbance torques, such as those due to a residual magnetic moment, have a significant effect on the attitude of spacecraft. In addition, hardware limitations make the task more challenging.
The effect of magnetic disturbances has shown itself by the problem of high tumbling rates observed on several CubeSat missions, post-flight analyses indicate that this is often due to un-modelled magnetic moments, mainly caused by the current flowing in the spacecraft, and the fact that CubeSats are often not designed with magnetic cleanliness in mind. However, by contrast, the other typical attitude disturbance sources for spacecraft (gravity gradient, aerodynamic, and solar radiation pressure torques) decrease significantly when the satellites become small.
We investigated in this research the source of the residual magnetic field in CubeSats and the effect of the resulting disturbance on the attitude of the spacecraft. It has been found that, although the disturbances may be minimised by good engineering practice, in terms of reducing the use of permeable materials and minimising current-loop areas, these disturbances can still be an issue when a high degree of stability is required. We, therefore, proposed a new technique using a network of magnetometers to characterise and then compensate the residual magnetic moment on the ground and in flight. A hardware prototype has been developed and successfully tested with the engineering model of the boom payload of Alsat-1N CubeSat, magnetic air coils, and permanent magnets in a Helmholtz coils arrangement by implementing a network of eight miniature 3-axis magnetometers. These are used to determine the strength, the centre, and the direction of the dipole of the magnetic source.
Gao Yang, Kruzelecky Roman, Murzionak Piotr, Lavoie Jonathan, Sinclair Ian, Schinn Gregory, Underwood Craig, Bridges Chris, Armellin Roberto, Lucca Fabris Andrea, Cloutis Edward, Leijtens Johan, Walker Roger, Vennekens Johan Lunar ?Volatile and Mineralogy Mapping Orbiter (VMMO)? Mission,Proceedings of the 70th International Astronautical Conference (IAC 2019)
International Astronautical Federation (IAF)
Human spaceflight to/on/from the Moon will benefit from exploitation of various in-situ resources such as water volatile and mineral. Evidence for water ice in Permanently Shadowed Regions (PSRs) on the Moon is both direct and indirect, and derives from multiple past missions including Lunar Prospector, Chandrayaan-1 and LCROSS. Recent lunar CubeSats missions proposed through the Space Launch Systems (SLS) such as Lunar Flashlight, LunaH-Map and Lunar Ice-Cube, will help improve our understanding of the spatial distribution of water ice in those lunar cold traps. However, the spatial resolution of the observations from these SLS missions is on the order of one to many kilometres. In other words, they can miss smaller (sub-km) surficial deposits or near-surface deposits of water ice. Given that future lunar landers or rovers destined for PSRs will likely have limited mobility (but improved landing precision), there is a need to improve the spatial accuracy of maps of water ice in PSRs. The VMMO (Volatiles and Mineralogy Mapping Orbiter) is a semiautonomous, low-cost 12U lunar Cubesat being developed by a multi-national team funded through European Space Agency (ESA) for mapping lunar volatiles and mineralogy at relatively high spatial resolutions. It has a potential launch in 2023 as part of the ESA/SSTL lunar communications pathfinder orbiter mission. This paper presents the work carried out so far on VMMO concept design and development including objectives, profile, operations and spacecraft payload and bus.