First In-Orbit Results from the UoSAT -12 Minisatellite

In 1995, having built and launched twelve 50-kg micro satellites, the Surrey Space Centre made a strategic decision to develop and demonstrate a larger low-cost satellite platform. This internally-funded project became the UoSAT-12 research and development minisatellite, a 325-kg satellite demonstrating key bus and payload technologies. On 21 April, a converted SS-18 Inter Continental Ballistic Missile (ICBM) placed Surrey\u27s UoSAT-12 minisatellite in a 650 km, 65° orbit. The in-orbit acquisition and check-out of the satellite have been successful. Engineers operating the satellite from Surrey\u27s mission control centre have received initial results from attitude control, remote sensing, Global Positioning System (GPS) orbit determination, L-to-S band communications and orbit station-keeping systems

Series of Satellite Encounters to Solve Autonomous Formation Assembly Problem

This paper addresses the problem of bringing two satellites on different orbital planes together and presents results of successful experiment done using two SSTL satellites: UoSat-2 and UoSat-12.A simple linearized Keplerian model with J2 dynamics included was used for initial approximation. A standard LQR controller is presented which by using the above model provides optimal along-track only firing strategy to bring the satellites within a few kilometres of each other. A high precision analytical propagation determines the exact geometry and time of closest approach. As the inclinations of the above two satellites differ by more than 30 degrees, the final step of bringing the two satellites into a stable formation was obviously left out, but radio receiver data from the fly-by are presented to validate the accuracy of the method. A nonlinear least squares filter was constructed to extract orbital elements from the radio data received, thus improving our knowledge of the relative orbits of the two satellites. We have brought the two satellites at closest 7.7 km, while other encounters happened at much larger distances. Clear radio signals were received when the satellites were even 150 km apart. For selected encounters for which we have good quality radio data, we were able to confirm that our prediction was 0.451 second accurate with respect timing and 2.29 km with respect closest approach distance (rms)

Microsatellite Constellation for Disaster Monitoring

Every year natural and manmade disasters cause devastation around the World through loss of life, widespread human suffering, and huge economic losses. Remote sensing satellites can contribute to mitigation of this devastation through early warning, event monitoring, and after-theevent studies. Unfortunately, present satellite remote sensing systems do not provide the high temporal resolution required for this activity. Additionally, the images they provide come at high cost per scene. The Surrey Space Centre at the University of Surrey has designed a constellation of remote sensing micro satellites that delivers 35 m ground resolution over a 600 km width scene in up to four spectral bands. Cost-benefit tradeoffs show that such images can fulfil many needs with the disaster monitoring community. However, spatial and spectral resolution are not the primary requirements for disaster monitoring; Disaster monitoring users demand high temporal resolution. Emerging manmade or natural disasters must be monitored on a daily basis if mitigation efforts are to be effective. Low-cost microsatellites applied in large constellations provide the only cost-effective solution to this design driver. This paper reports the details of Surrey\u27s Disaster Monitoring Constellation, describing the key subsystem technologies which deliver the desired price/performance ratio, and the overall system design which exploits the low unit cost of micro satellites to deliver a large constellation in affordable and useful increments

Affordable Access To Space – Getting There

To realise the full potential of modern low cost mini-micro-nano-satellite missions, regular and affordable launch opportunities are required. It is simply not economic to launch satellites of 5-300kg on single dedicated launchers costing typically $10-20M per launch. Whilst there have been periodic \u27piggy-back\u27 launches of small satellites on US launchers, these have been infrequent and often experienced significant delays due the vagaries of the main (paying!) payload. In 1988, Arianespace provided a critical catalyst to the microsatellite community when it developed the ASAP platform on Ariane-4 providing, for the first time, a standard interface with affordable commercial launch contracts for small payloads up to 50kg. Some 20 small satellites have since been launched on the Ariane-4 ASAP ring, however as most of these microsatellite missions seek low Earth orbit (especially sun-synchronous) the number of prime missions into these orbit has declined since 1996 and with it the useful low cost launch opportunities for microsatellites. Whilst Ariane-5 has an enhanced capacity ASAP, it has yet to be widely used due to the infrequent launches, higher costs, and the unpopularity of the GTO orbit required by the majority of customers. China, Japan and India have also provided occasional launches for small payloads, but not yet on a regular basis. Fortunately, the growing interest and demand for microsatellites coincided with the emergence of regular, low cost launch opportunities from the former Soviet Union (FSU) - both as secondary \u27piggy-back\u27 missions or as multiple microsatellite payloads on converted military ICBMs. Indeed, the FSU now supplies the only affordable means of launching minisatellites (200-500kg) into LEO as dedicated missions on converted missiles as these larger \u27small satellites\u27 are often too big to be carried \u27piggy-back\u27. The entrepreneurial effort of leading FSU rocket & missile organisations has taken over providing launches for the small satellite community with an excellent track record. However, negotiating and completing a Launch Services Contract for a micro-minisatellite with any launcher organisation is a complex matter and risky territory for the unwary or inexperienced - who may fall prey to unexpected costs and delays. Whilst this warning should be heeded when dealing with European and US organisations, it is particularly relevant to negotiating launches from the FSU where there is a plethora of agencies and organisations providing a bewildering range of launch vehicles and options. Furthermore, the FSU has developed a very different technical and managerial philosophy towards launchers when compared with the West and this can be unnerving to \u27first-time buyers\u27. Organisations experienced in dealing in the FSU will encounter an excellent service - once the launch service agreement has been thoroughly and fiercely negotiated in every detail. Inexperienced buyers have encountered delays, lost opportunities, unexpected taxes, additional cost for services or facilities not originally specified, and frustration at the different procedures used in the FSU. Fortunately, all this can be avoided and the FSU is the current mainstay for launching small satellites quickly, affordably and reliably. SSTL has unique experience gathered over 22 years in handling launches for small satellites, ranging from a 6kg nanosatellite, 50-120kg microsatellites, and a 325kg minisatellite, using 7 different launchers from the USA, Russia, Ukraine, and Europe. This experience, and working closely with organisations in the FSU, has enabled SSTL to provide good value launches for its small satellite customers without delay and with an excellent launch success. The paper will describe the experience gained by Surrey, across the various launch providers, in successfully launching 21 small satellites - affordably, reliably and quickly. It will highlight the key factors that are necessary to ensure a \u27good experience\u27

One Year in Space: Results from PoSAT-1

PoSAT-1 was launched in September 1993, joining the UoSAT family of spacecraft already in orbit. Built by Surrey Satellite Technology Ltd. (SSTL) for a consortium of Portuguese industry, PoSAT-1 represents the latest generation of UoSAT microsatellites. This paper will briefly review the development and evolution of the UoSAT design. It will then summarize key functional parameters of PoSAT-1 including attitude determination and control, electrical power, data handling systems, thermal control and communications. PoSAT-1 contains a variety of experiments including CCD wide and narrow field Earth imaging cameras, a star field sensor, a GPS receiver, cosmic radiation and total radiation dose detectors, and a digital signal processing (DSP) experiment. Results from all these experiments will be highlighted. The paper concludes with future UoSAT/SSTL research and development efforts

Low Cost Propulsion Development for Small Satellites at the Surrey Space Centre

The Surrey Space Centre (SSC) has led the way in demonstrating the utility of microsatellite size spacecraft for research, humanitarian, commercial, and military applications. SSC recognises that cost effective propulsion technology for small spacecraft is an enabling technology for expanding the utility of these assets and has been actively researching this field since 1993. This paper provides an overview of propulsion research and development at the Surrey Space Centre. The paper will summarise SSC goals for small spacecraft propulsion technology and link them to areas of propulsion research past, present and future. A review of Surrey\u27s propulsion history to include hybrid, monopropellant, cold gas and resistojet technology is presented. Design and integration of SSC cold gas and resistojet technologies on flight spacecraft will also be covered with an emphasis on the SSC low cost approach to qualification, integration and operation of these systems. These topics will be followed by a discussion of areas that are currently being investigated for near term research, specifically, H202 long term storage, expulsion, catalysis, Green monopropellant and hybrid technology utilising both N20 and H202. One topic covered in detail is a novel alternative geometry hybrid rocket motor. This motor is currently under development to provide a low-cost, intrinsically-safe and easy to integrate orbital upper-stage for small spacecraft. A prototype motor has been constructed and test results are presented

A Nanosatellite to Demonstrate GPS Oceanography Reflectometry

This paper describes a proposal for a rapid, low cost, nanosatellite mission to demonstrate the concept of GPS ocean reflectometry and to investigate the feasibility of determining sea state for a future operational space-based storm warning systems. The aims of this mission are to prove the general feasibility of GPS ocean reflectometry, to demonstrate sea state determination and to enable the development of a practical GPS ocean reflectometry payload for future missions. The payloads on the satellite consist of a 24 channel C/A code SGR-10 space GPS receiver and a solid state data recorder. The GPS receiver has one standard RHCP zenith antenna, and one high gain LHCP nadir antenna for receiving the reflected signals. A dual approach is taken to measurement gathering. Initially, bursts of directly sampled IF data are stored and downloaded to permit processing of the data on the ground. Later in the mission, the GPS receiver software may be modified to permit the processing of signals on-board the satellite. The nanosatellite is based on SSTL’s SNAP design and has a projected total mass of around 12 kilograms; orbit average power of approximately 4.8 watts; 3-axis attitude control to 1-2 degrees; VHF uplink, S-band downlink at 500 kbps, and OBC based on the StrongARM SA1100. Using the SNAP design enables a fast manufacture at low cost: estimated at 9 months and around 2 million Euros, including launch. The proposed mission makes use of the Surrey Space Centre Mission Control ground-station in Guildford (UK) for control and data gathering. Surrey Satellite Technology Ltd (SSTL) is a world leader in both nanosatellite and GPS technology for small satellites. SSTL’s highly successful SNAP-1 nanosatellite launched in June 2000 demonstrated the potential of such small spacecraft, and this proposal involves the first ever use of a nanosatellite for a commercial application (GANDER) in collaboration with SOS Ltd (UK) a company specialising in oceanography from space

A Novel Method for Achieving SAR Imaging with a Pair of Micro-Satellites by Means of a Bi-Static Configuration

There is increasing interest in the potential capabilities and applications of micro -satellites in the field of Earth-observation (EO). Passive optical imaging is now well established on such platforms, however, an active imaging payload - a synthetic aperture radar (SAR) - would appear to be insupportable, due to its size, complexity and high -power requirements. A major driver of these requirements is that traditional SAR systems use backscatter - which is necessarily weak from most terrain types. If the forward scattered energy could be gathered, then the transmit-power requirements could drop significantly. We therefore propose a novel method by which two micro-satellites fly in formation to accomplish a SAR mission bi-statically. The transmitting satellite will be the “master”, with the receiver satellite “slaved” off it by means of a synchronization signal. The satellites image a swath of 30 km, at a ground resolution of 30 m from 700 km altitude. Our constellation geometry can image anywhere in a pre-selected latitude band, and requires minimal orbit-control resources. The viewing configuration resolves the left-right ambiguity that occurs in near nadir pointing bi-static radar. Applications to a polar ice-monitoring mission are discussed, although with minor changes any location on Earth can be viewed

Specifics of Small Satellite Propulsion: Part 1

Small satellite propulsion is a subject of unique constraints and requirements. Based on University of Surrey experience in small satellite building and operation, these features are listed and explained. Available volume is often identified as the most severe constraint for a small satellite with power and cost being the other two major constraints. Mass is often only of secondary importance for small satellites. Propulsion dry mass fraction for a spacecraft grows upon the system scaling-down. For small spacecraft propulsion fraction can easily exceed 85%. In such a case, a combination of independent systems for multifunctional propulsion mission scenarios would aggravate the situation. Moreover, specific impulse is not a factor reflecting small satellite propulsion system performance since spacecraft velocity change is also a function of propulsion dry mass fraction. New conceptual and design solutions are suggested for small satellite propulsion with respect to its specific constraints and requirements. Features of future advanced, low-cost propulsion system for small satellite are described

Right-sizing Small Satellites

Spacecraft standardization has been a topic of great debate within the space community. This paper intends to be a provocative thought piece asking one fundamental question: “is there a ‘right size’ for small satellites?” In order to answer this question, we propose three top-down design factors for the space systems engineering process: spacecraft utility, mission utility, and optimum cost. Spacecraft utility quantitatively measures the capability of a spacecraft, derived from its volume and power properties. Mission utility then measures the aggregate value of a constellation. Optimum cost, which is a function of spacecraft mass and quantity, can be determined by assessing the break-even point. Data from the small satellite community, including USAF Academy FalconSAT and Surrey Satellite Technology Ltd. (SSTL) missions, is presented in support of this discussion, constrained to systems with a mass less than 200 kg. These design factors inform the mission developer in determining the appropriate system architecture. Using these design factors, a notional standardized spacecraft configuration is presented, with a mass of 30 kg and 50 cm cubed volume that optimizes spacecraft utility, mission utility, and cost