Surrey Satellite Technology Ltd Research Articles

ANALYSIS OF NOVASAR-1 S-BAND DATA IN DEVELOPING AN ALTERNATIVE LAND COVER MAPPING

Abstract. The Advanced Science and Technology Institute of the Department of Science and Technology (DOST-ASTI), through its Synthetic Aperture Radar and Automatic Identification System (SARwAIS) Project, has gained access to S-Band SAR images acquired by the NovaSAR-1 satellite of UK’s Surrey Satellite Technology Ltd. (SSTL) To help maximize the utility of these images especially in the aspect of terrain-related applications, their viability as potential alternatives to datasets like optical satellite images and other SAR images in characterizing land cover types was evaluated. Statistical analyses on the backscatter values from the tri-polarization ScanSAR datasets using Multivariate Analysis of Variance (MANOVA) and its corresponding post-hoc tests showed that there is a significant difference on the mean backscatter values at 0.05 level of significance. Moreover, Tukey’s honestly significant difference (Tukey’s HSD) test determined which pairs contribute to the significant difference. Using the Random Forest algorithm resulted in an accuracy of 66.93% without further optimization and/or reduction in the number of land covers being classified. Despite the relatively unremarkable accuracy score, it still showed potential for data augmentation with optical satellites for land cover mapping and other terrain-related applications.

Active debris removal: A review and case study on LEOPARD Phase 0-A mission

The growing number of space debris is alarming as it threatens space-borne services. Hence, there is an increasing demand to remove space debris to ensure sustainability and protect valuable orbital assets. Over the past few years, the research community, agencies and industries have studied many passive and active debris removal methods. However, the current technology readiness for space debris removal is still low. This paper first presents a comparative study of various space debris removal technologies to address the knowledge gap and quantify the challenges. This paper reviews the current state-of-the-art space technologies relevant to Active Debris Removal (ADR) missions. Detailed trade-off analysis is then presented based on the Low Earth Orbit Pursuit for Active Removal of Debris (LEOPARD) Phase 0-A study; this study is part of the United Kingdom (UK) Space Agency’s Active Debris Removal programme. The ADR mission scenario considered in this paper comprises a chaser spacecraft equipped with recommended technologies to capture non-cooperative targets safely. The final capture technology for the LEOPARD mission consists of an active robotic manipulator and a passive net capture mechanism. An analysis of the coupled-body dynamics of the chaser spacecraft carrying the robot manipulator and the targeted debris is carried out in simulation using SimscapeTM. The chaser spacecraft comprises Airbus’s Versatile In-Space and Planetary Arm (VISPA) mounted on a base spacecraft from Surrey Satellite Technology Ltd. (SSTL); the targeted debris is SSTL’s Tactical Operational Satellite (TOPSAT). The simulation results show dynamic changes in the chaser robot and the target satellite while performing non-cooperative capture. The simulation study accounted for various operational scenarios where the target is stationary or in motion. Further, for different modes of operation, the worst-case end-effector capture force limits were determined using open-loop control to execute a safe capture. Overall, the results presented in the paper advance the current state-of-the-art of robotic ADR and offer a significant leap in designing close-range motion and force control for stabilising the coupled multi-body system during capture and post-capture phases. In summary, this paper pinpoints the technological gaps, identifies barriers to realising ADR missions and offers solutions to catalyse technology maturity for protecting the space ecosystem.

Ground and flight tests of AlSat-1B butane propulsion system

On September 26, 2016 Algerian Space Agency launched AlSat-1B, the second in a series of medium resolution earth observation satellites mission. AlSat-1B electro-thermal propulsion system follows the classic design principle that has been used on previous SSTL-100 missions. With a total dry weight of 5.17 kg, the system is filled with 2.35 L self-pressurized butane. The thruster assembly is designed to use 15 W (at 28 V) redundant heater elements, it is designed to have an average mission thrust of 50 mN. With a warm up time of 10 min, the temperature of the butane will be increased by over 250 °C. This is the equivalent of about 35% gain in specific impulse over ambient temperature butane. The spacecraft dry weigh at launch site was 107 kg, the propulsion system is designed to provide at least 19 m/s Delta-v to meet the spacecraft's mission requirement. To investigate the system readiness for flight, a series of performance tests have been completed at the Surrey Satellite Technology Ltd laboratories (United Kingdom), Satellite Development Centre (Algeria) and Satish Dhawan Space Centre rocket launch site (India), the results of these tests as well as initial flight test results are presented in this paper.

Towards Deep Simulations of LEO Satellite Links Based-on Saratoga

Satellites, in low earth orbit, are increasingly deployed in last years. They are used as well various space missions and mostly in remote sensing missions. Despite this growing interest and the large number of deployed satellites, each space mission has its own requirements according the purposed activities. Engineers are called-upon to develop new codes, algorithms, and to bring changes to the manufacturer’s technology. Initially, the new developed features are implemented on test-beds for the assessment purposes, however, emulation platforms are expensive and their implementation time consuming. Simulation models give the first try out and overcome some issues by giving an agility for a wide range of experimentations in short time, while having a lower cost. In this context, we present a contribution on the widely used simulator by scientific researcher community NS-2. The contribution consists to model the wireless communications between satellites and ground stations based-on SSTL (Surrey Satellite Technology Ltd) technology. We present the setting-up of additional physical layer modules required to model the radio links in space missions and antenna features; we describe, in addition, the developed module to model the Saratoga transfer protocol as an application layer. Evaluation of the developed modules on NS-2 is performed by simulations and comparisons to the referenced simulator in space industry STK and the realistic data collected from the operational mission Alsat-1B.

Stability Evaluation of the SDRE Technique based on Java in a CubeSat Attitude and Orbit Control Subsystem

In 2013, the STRaND (University of Surrey and Surrey Satellite Technology Ltd) and the PhoneSat (NASA) programs attracted the attention of the aerospace community applying commercial off-the-shelf smartphones in CubeSats. Both programs deployed CubeSats using smartphones based on Google's Android, in which application development is mainly based on Java programming language. Some of these CubeSats had actuators, e.g., STRaND-1 had three reaction wheels mounted in an orthogonal configuration to provide three-axis control, whereas PhoneSat 2.0 beta had magnetorquers to de-tumble the spacecraft. Taking into account a CubeSat that runs Android operating system (based on a smartphone), it is natural to evaluate the attitude and orbit control subsystem (AOCS) based on Java. Elsewhere, we shown State-Dependent Riccati Equation (SDRE) is a feasible non-linear control technique that can be applied in such CubeSats using Java. Moreover, we shown, through simulation using a Monte Carlo perturbation model, SDRE provides better performance than the PID controller, a linear control technique. In this paper, we tackle the next fundamental problem: stability. We evaluate stability from two perspectives: (1) parametric uncertainty of the inertia tensor and (2) a Monte Carlo perturbation model based on a uniform attitude probability distribution. Through the combination of these two perspectives, we grasp the stability properties of SDRE in a broader sense. In order to handle the uncertainty appropriately, we combine SDRE with H∞. The Nanosatellite Constellation for Environmental Data Collection (CONASAT), a CubeSat from the Brazilian National Institute for Space Research (INPE), provided the nominal parameters for the simulations. The initial results of the simulations shown that the SDRE controller is stable to ± 20% uncertainty in the inertia tensor for attitudes uniformly distributed and angular velocity up to 0.15 radians/second.

EARTH OBSERVATION APPLICATIONS FOR GOAL 14: IMPROVING MARITIME DOMAIN AWARENESS USING SYNTHETIC APERTURE RADAR IMAGING WITH AUTOMATIC IDENTIFICATION SYSTEM IN THE PHILIPPINES

Abstract. The Philippines has acquired access to the NovaSAR-1 satellite developed by Surrey Satellite Technology, Ltd. (SSTL) for the implementation of its project Synthetic Aperture Radar (SAR) and Automatic Identification System (AIS) for Innovative Terrestrial Monitoring and Maritime Surveillance, which will provide simultaneous S-band SAR imaging with AIS data for applications targeted on improving maritime domain awareness. The country has inherent challenges in this field due to its archipelagic nature, with earth observation seen as a potential solution as it provides an immediate and wide coverage over designated priority areas. This contributes toward achieving Sustainable Development Goal 14: Life Below Water by providing objective information in support of data-driven decision and policymaking, closing knowledge gaps in monitoring Philippine waters.

Topology Optimization for Additive Manufacturing as an Enabler for Light Weight Flight Hardware

Three case studies utilizing topology optimization and Additive Manufacturing for the development of space flight hardware are described. The Additive Manufacturing (AM) modality that was used in this work is powder bed laser based fusion. The case studies correspond to the redesign and manufacture of two heritage parts for a Surrey Satellite Technology LTD (SSTL) Technology Demonstrator Space Mission that are currently functioning in orbit (case studies 1 and 2), and a system of five components for the SpaceIL’s lunar launch vehicle planned for launch in the near future (case study 3). In each case, the nominal or heritage part has undergone topology optimization, incorporating the AM manufacturing constraints that include: minimization of support structures, ability to remove unsintered powder, and minimization of heat transfer jumps that will cause artifact warpage. To this end the topology optimization exercise must be coupled to the Additive Manufacturing build direction, and steps are incorporated to integrate the AM constraints. After design verification by successfully passing a Finite Element Analysis routine, the components have been fabricated and the AM artifacts and in-process testing coupons have undergone verification and qualification testing in order to deliver structural components that are suitable for their respective missions.

Satellite expertise overhead

The UK space industry is booming. No sooner did Guildford-based Surrey Satellite Technology Ltd unveil its new 3,700 m2 satellite clean-room facility, than the European Commission chose the company to assemble the next batch of eight Galileo satellite navigation payloads adding to the 14 that it is already building.

Experience with Delay‐Tolerant Networking from orbit

AbstractWe describe the first use from space of the Bundle Protocol for Delay‐Tolerant Networking (DTN) and lessons learned from experiments made and experience gained with this protocol. The Disaster Monitoring Constellation (DMC), constructed by Surrey Satellite Technology Ltd (SSTL), is a multiple‐satellite Earth‐imaging low‐Earth‐orbit sensor network in which recorded image swaths are stored onboard each satellite and later downloaded from the satellite payloads to a ground station. Store‐and‐forward of images with capture and later download gives each satellite the characteristics of a node in a disruption‐tolerant network. Originally developed for the ‘Interplanetary Internet,’ DTNs are now under investigation in an Internet Research Task Force (IRTF) DTN research group (RG), which has developed a ‘bundle’ architecture and protocol. The DMC is technically advanced in its adoption of the Internet Protocol (IP) for its imaging payloads and for satellite command and control, based around reuse of commercial networking and link protocols. These satellites' use of IP has enabled earlier experiments with the Cisco router in Low Earth Orbit (CLEO) onboard the constellation's UK‐DMC satellite. Earth images are downloaded from the satellites using a custom IP‐based high‐speed transfer protocol developed by SSTL, Saratoga, which tolerates unusual link environments. Saratoga has been documented in the Internet Engineering Task Force (IETF) for wider adoption. We experiment with the use of DTNRG bundle concepts onboard the UK‐DMC satellite, by examining how Saratoga can be used as a DTN ‘convergence layer’ to carry the DTNRG Bundle Protocol, so that sensor images can be delivered to ground stations and beyond as bundles. Our practical experience with the first successful use of the DTNRG Bundle Protocol in a space environment gives us insights into the design of the Bundle Protocol and enables us to identify issues that must be addressed before wider deployment of the Bundle Protocol. Published in 2010 by John Wiley & Sons, Ltd.

An overview of small satellites in remote sensing*

This article gives a global overview of some aspects of small satellite developments since the launch of Sputnik‐1 50 years ago. These developments are offering new opportunities for remote sensing. *. Based on a paper presented at the International Workshop on Earth Observation Small Satellites for Remote Sensing Applications, Kuala Lumpur, Malaysia, 20–23 November 2007. The earliest satellites were small but, as time went on, the satellites that were flown were developed to serve several different projects and they became larger and more expensive and took a long time to design, build and be launched. One of the extreme examples was Envisat. For these large satellites compromises often had to be made between different objectives and different instruments. A failure of the whole system meant the death of many different projects. The future is likely to see more small satellites, each of which is dedicated to a particular mission objective and carries a single instrument. Through this approach more and more countries around the world are becoming involved in Earth observation from space, not just in using the data from the major established systems but also in constructing their own systems. There were some small, low‐cost satellites in the early days, but they were overlooked or considered toys by the space community. The first microsatellites were built by enthusiasts of the amateur radio community and launched in the early 1960s. The invention/introduction of the microprocessor in the 1970s represented a quantum jump for the onboard capabilities of a spacecraft. This technology introduction represented a prime catalyst in the development of microsatellites since it enabled small physical structures in support of sophisticated data handling applications. The engineering of microsatellites, which emerged in the early 1980s, took a radical change of approach from the custom design of traditional spacecraft, namely a design‐to‐capability scheme to achieve cost reductions by focusing on available, and existing technologies using a general purpose bus and ‘off‐the‐shelf’ components and instruments. The new approach of small satellite design was pioneered by Surrey Satellite Technology Ltd (SSTL) of Surrey University, UK. SSTL's lead has now been followed by various companies and space agencies throughout the world. A key feature of this work is the development of microsatellite technology transfer programmes, providing partnerships and on‐the‐job training of engineers and scientists of foreign national organizations in cooperative programmes – in particular to those who were not in a position to start or afford their own space projects – to participate in the development of their own microsatellites. In addition to discussing these developments, this article also covers small satellite classification, small satellite initiatives in the USA, small satellite development in the rest of the world, some aspects of the technology and applications of small satellites, and small satellites developed by universities, particularly the CubeSats programme. Today, small satellites are changing the economics of space. These spacecraft embrace cutting edge Commercial Off‐The‐Shelf (COTS) technology, permitting novel and less‐expensive ways to perform meaningful observation missions, although there are various technical challenges. There are several synthetic aperture radar (SAR) and hyperspectral imaging missions on small satellites in operation and in planning.

Lunar science with affordable small spacecraft technologies: MoonLITE and Moonraker

Returning to the Moon has been advocated by a large number of international planetary scientists in order to answer several key scientific questions. The UK also has an active lunar science community keen to support (robotic) lunar exploration missions. However, for several years these interests have been eclipsed by the drive to Mars. Recently there is a renewed global interest in the Moon demonstrated by the Vision for Space Exploration in the USA, the evolving Global Exploration Partnership, and new lunar missions from Europe, Japan, China, India and the USA. The ESA Aurora programme may also broaden its focus to embrace the Moon as well as Mars—realizing that the risks associated with many of the major technical challenges that are faced by Mars missions could be reduced by relatively inexpensive and timely lunar technology tests. Surrey Satellite Technology Ltd. (SSTL) and Surrey Space Centre (SSC) have been preparing a ‘smallsat’ approach [ Sweeting, M.N., Underwood, C.I., 2003. Small-satellite engineering and applications. In: Fortescue, P., Stark, J., Swinerd, G., (Eds.), Spacecraft Systems Engineering, third edition. Wiley, New York, pp. 581–612] to achieving a low-cost lunar mission for more than a decade—including various activities, such as the earlier LunarSat study funded by ESA and a current hardware contribution to the Chandrayaan-1 mission. With the recent successes in GIOVE-A, TOPSAT and BEIJING-1, 1 1 Recent Earth satellite missions built and launched by SSTL. alongside participation in Aurora and Chandrayaan-1, Surrey have developed capabilities for providing affordable engineering solutions to space exploration. Recently, SSTL/SSC was funded by the UK Particle Physics and Astronomy Research Council (PPARC) (now subsumed into the UK Science and Technology Facilities Council) to undertake a study on low-cost lunar mission concepts that could address key scientific questions. This paper presents some major results from this study [Phipps and Gao, 2006. Lunar mission options study. UK Particle Physics and Astronomy Research Council Report Reference No. 118537, pp. 1–104] and provides preliminary definitions of two mission proposals.

Which way to the Moon?

A PPARC-led delegation comprising David Parker (BNSC/PPARC Director of Science), Prof. Sir Martin Sweeting (Surrey Satellite Technology Ltd), Ian Crawford (Birkbeck College) and Andrew Ball (Open University) attended the NASA Strategy Workshop in Washington DC, from 25 - 28 April 2006 (http:// www. aiaa. org/ events/ expwkshp). NASA initiated the workshop as a first step in its activities during 2006 to define a strategy for lunar exploration, building on the for Space Exploration announced in 2004 ( http:// www. nasa.gov/ mission_ pages/ exploration/ main/ and http:// exploration. nasa. gov/). Given the backdrop of the Vision framework, the goal was to bring together the reasons we ( meaning humanity) are going back to the Moon and we want to do there. For many, the answers to these questions have been clear, albeit diverse, for a long time, being articulated and updated in various forms over the years (e.g. ESA 1992, 2003; Spudis 1996, 2001; Crawford 2004a, b; Stern 2005). The answers to the why and what questions reflect a wide variety of scientific, technological, commercial and societal motivations.

GPS/GNSS reflectometry nanosatellite demonstration mission

Loss of life, injury and huge economic losses are incurred annually due to irregular and insufficient sea–state information. Figures indicate that, each year, the marine insurance industry pays out over $2 billion in claims for weather–related accidents, while bad weather causes one ship of over 500 t to sink somewhere on the globe every week. Accurate knowledge of local ocean conditions is therefore crucial in providing forecasts and early warnings of severe weather conditions. Space–borne systems, particularly satellites, provide the ideal platform for global monitoring of sea conditions via altimetric measurements. As an alternative to active altimetry, another concept is passively receiving reflected signals from the Global Positioning System (GPS) and other Global Navigation Satellite System (GNSS) satellites. This concept was first developed by Dr Manuel Martin–Neira at ESA–ESTEC. ESA9s Passive Reflectometry and Interferometry System makes use of GPS/GNSS signals from satellites and their reflection off the ocean surface to derive oceanic properties such as surface height, significant wave height, wind speed and wind direction. Surrey Satellite Technology Ltd are proposing a nanosatellite demonstration mission to ascertain the feasibility of the GPS ocean reflectometry concept.

Cost effective propulsion systems for small satellites using butane propellant

This paper will describe the work performed at the Surrey Space Centre to produce cost effective propulsion systems for small spacecraft with relatively low deltaV (ΔV) requirements. Traditionally, cold gas nitrogen systems have been used for this type of application, however they have high storage volume requirements. This can be a problem on small spacecraft, which are typically volume limited. An alternative solution is to use liquefied gases, which store as liquids, hence have reasonable density levels, and can be used in a cold gas thruster. At the Surrey Space Centre, butane has been selected as the propellant of choice. Although it has slightly lower specific impulse performance than nitrogen, it has a significantly higher storage density and it stores at a very low pressure, hence no regulation system is required. On 28 th June 2000 Surrey Satellite Technology Ltd (SSTL) launched it first nanosatellite SNAP-1. This 6.5kg spacecraft was equipped with a small cold gas propulsion system utilising 32.6 grams of butane propellant. During the propulsion system operation phase the spacecraft's semi major axis was raised by nearly 4 kilometers using the propulsion system. The design of the propulsion system will be described and the low cost features highlighted. Telemetry data will be used to describe the propulsion operations and an overall mission specific impulse will be derived. SSTL are currently under contract to build three Earth observation spacecraft for a Disaster Monitoring Constellation (DMC). Each spacecraft will weigh approx 100 kg and have a ΔV requirement of 10 m/sec. A butane system has been designed and manufactured to meet the requirements of these spacecraft. The system is based very much on the flight heritage of the SNAP-1 system, with the addition of greater propellant storage capacity. The lessons learnt from the SNAP-1 operation will be reviewed and the resulting design improvements on the DMC propulsion systems will be detailed.

Second generation disaster-monitoring microsatellite platform

Earth Observation satellites have traditionally been expensive to develop and launch and, as a consequence, have been targeted to cover the diverse needs of a large user community. Many niche applications in remote sensing are not exploited to their full potential or operating on a profitable basis and, as a result, space-based Earth Observation has not yet made a similar impact into our everyday lives when compared with satellite communications. Small satellite technology however has come of age and Earth observation instrument technology has advanced to levels permitting high quality sensors to be flown on small inexpensive satellite platforms. Many examples of such missions have returned increasingly sophisticated imagery and have been well documented. As well as offering in-orbit ‘shutter control’ to small groups and specialist organisations, these satellites can be individually tailored to specific applications with custom sensors, filters, swath width, and Ground Sampling Distance. Surrey Satellite Technology Ltd. (SSTL) has been at the forefront of developing innovative Earth Observation missions for the past decade, using small satellites covering a mass range of 5kg to 300kg. Recent missions have demonstrated remote inspection, high quality multispectral imaging at Ground Sampling Distances (GSD) of 30m and panchromatic imaging at a GSD of 10m. Currently a disaster-monitoring network of five microsatellites is under construction by SSTL within an international partnership to capitalise on these small satellite capabilities. It will offer a system with a temporal resolution of daily global coverage providing rapid multi-spectral imagery of wide-swath 30m GSD to the disaster relief community. In order to expand the capabilities of such a network, Surrey is now developing a follow-on network based on a second-generation spacecraft platform, and a small satellite platform has been developed specifically to meet generic small satellite Earth Observation applications as part of a constellation. It allows the visible-band imaging network under development to be expanded to serve more advanced applications within disaster monitoring with sensors such as IR, ocean colour, hyperspectral, high resolution imagery, and even Synthetic Aperture Radar.

The Topsat satellite

This paper discusses the Topsat satellite, currently being built by a partnership between DERA Space, Rutherford Appleton Laboratory, Surrey Satellite Technology Ltd and InfoTerra Ltd (Formerly NRSC). Topsat will have the capability to provide imagery at 25m panchromatic and 5m colour resolution, direct to the user at a mobile ground station, from a 125kg microsatellite in low Earth orbit. Its low‐cost philosophy includes wide use of commercial off‐the‐shelf components and the goal of a one‐year mission life.

Surrey Satellite Technology Ltd scores UK first

Surrey Satellite Technology Ltd scores UK first

UoSAT-12 minisatellite for high performance earth observation at low cost

Surrey Satellite Technology Ltd (SSTL) at the University of Surrey (UK) has pioneered cost-effective satellite engineering techniques for smaller, faster and cheaper satellites to provide affordable access to space. SSTL has designed, built, launched and operated a series of twelve 50 kg microsatellites in low Earth orbit which carry a wide range of satellite communications, space science, remote sensing and in-orbit technology demonstration payloads—for both civil and military applications. Eight of SSTL’s microsatellites have carried CCD Earth imaging cameras, coupled with powerful onboard processing computers which have demonstrated the capability of this new generation of low-cost, rapid-response, modern small satellites. SSTL has recently developed an advanced 250 kg minisatellite platform to meet the needs of future low-cost Earth observation and remote sensing applications. With enhanced payload mass and volume, attitude stability and communications capabilities, this new platform will support more sophisticated payloads than the minimalist microsatellites. The experimental UoSAT-12 mission, to be launched into LEO in 1997, will carry high resolution and multispectral remote sensing payloads to demonstrate imaging not currently practicable on existing microsatellites. This paper reviews the design and characteristics of the UoSAT-12 imaging payloads which include multispectral cameras providing 40 m ground resolution with an 80 km swath width, and a panchromatic imaging instrument providing 10 m resolution. The trade-off between linear pushbroom sensors and area CCD cameras, and the role of on-board processing for automatic image processing is presented. These techniques enable small, low-cost minisatellites to approach the performance of conventional Earth observation satellites—but at a fraction of the cost. This pioneering work by Surrey on advanced microsatellites and minisatellites has resulted in imaging missions that can respond rapidly to customer requirements, which are affordable to a far wider community of individual commercial or governmental organizations, and which provide emerging space nations with an independent Earth observation capability.

Earth observation using low cost micro/minisatellites

Surrey Satellite Technology Ltd (SSTL) at the University of Surrey (UK) has pioneered cost-effective satellite engineering techniques for smaller, faster, cheaper satellites to provide affordable access to space. SSTL has designed, built, launched and operated a series of twelve 50kg microsatellites in low Earth orbit which carry a wide range of satellite communications, space science, remote sensing and in-orbit technology demonstration payloads — for both civil and military applications. Each of these has been built and launched for around US$3M. This paper reviews SSTL's remote sensing capabilities and presents image results from the microsatellite cameras in low Earth in orbit. The latest microsatellites (TMSAT & FASat-Bravo) under construction at SSTL and due for launch in mid-1997 will provide 3-band multispectral imaging with 80-metre resolution; autonomous on-board image analysis, processing and compression prior to transmission direct to ground-based users employing small portable terminals.