Delegates were welcomed by Graham Davison, the Manager of Space Department to the Whittle theatre at DERA's new Cody building. He expressed his delight at the enthusiastic response from both the Royal Aeronautical Society (RAeS) and the British Interplanetary Society (BIS) to the initiative to hold the symposium which came at a most suitable time. In recent years, the UK has played a significant role in the development of small satellite missions. As a result, satellites of less than 100 kg mass were now performing useful operational missions in addition to flight demonstrations to bring new technologies to the market place. NASA and ESA are investing increasingly in small satellite programmes because they recognise the value for money in low-cost, short timescale missions. DERA's aim was to collaborate with industry to help realise these benefits.
During the first session, entitled the technology needed by small satellites, four presenters reviewed the factors which can make small satellites competitive and some of the emerging techniques which were being exploited. Keith Clark, senior engineer at Surrey Satellites Technology Limited (SSTL), described how his company was exploiting its experience of 16 micro-satellite programmes (25 kg to 100 kg), of which 12 are in orbit and four due to be launched next year, to build a mini-satellite in the 250 to 500 kg range. Costs could be kept to a minimum by using many of the electronics and communications features developed for micro-satellites while accommodating payloads of up to 150 kg. The spacecraft would be capable of low earth orbit (LEO) or interplanetary missions and the moon was a possible objective. Mike Slim from AEA Technology then described how the development of the lithium ion (LION) battery offered further cost-effective benefits both to small and large satellites. At half the mass and volume of Nickel Cadmium or other alternatives, the high charge efficiency of the batteries is very attractive. Extensive flight qualification of a design for the DERA space technology research vehicle (STRV) programme had shown the batteries to be robust, have high longevity and be suitable for use in LEO and geostationary orbit (GEO). The next objective was to develop a larger battery for large communications satellites as part of a national programme.
Henry Halvajian, from the Aerospace Corporation in Los Angeles, provided a fascinating insight into the application of laser etching techniques, developed in the micro-electronics industry, to fabrication nano-satellite systems. Nano satellites are of less than 5 Kg mass and are expected to be developed for deployment from a ‘mother’ satellite for short duration inspection or data gathering missions during the flight of the mother. They offer a very cost effective means to monitor sudden changes in environmental conditions, to deploy as an ‘antenna’ or to view spacecraft in orbit remotely. Constructed on silicon wafers, both electronic and mechanical features are etched by computer controlled lasers in the same way that micro-chips are manufactured. Finally Kim Ward from Space Innovations Limited (SIL) described how small satellites were beginning to perform the same functions as their larger equivalents. SIL have used their experience in building small spacecraft sub-systems to develop a LEG approach to small satellite and ground segment construction. He also explained that SIL designs were based on flexible interfaces which enabled their sub assemblies either to fit together or to be easily adapted to interface with other units. Currently his company was working with the European Space Agency on the PROBA programme (described later) and researching potential small satellite applications for the Department of Trade and Industry.
After lunch and a tour of the DERA space test and Ion Propulsion Development facilities, Mr Roberto Aceti, Head of in-orbit technology demonstration at the European Space Agency Technical Centre (ESTEC), chaired the final session, the ‘use of small satellites for proving new technology. He started by outlining ESA's commitment to small satellite programmes and illustrated this commitment with the Smart One and PROBA missions. Smart One is an interplanetary mission for the year 2000 which will demonstrate, among other new technologies, electric propulsion advanced power systems and novel control techniques. The ESA project for on board autonomy (PROBA) is a LEO mission designed to demonstrate a wide range of technical developments for improving satellite autonomy. Although only a micro-satellite, PROBA will have tri-axis stabilisation, an operational payload and a smart onboard processing system capable of managing the spacecraft and its payload independently of ground control for sustained periods. One of the key developments is the onboard Sparc processor whose application is being developed with SIL. The successful demonstration of this 32 bit processor with gigabits of onboard memory lend a completely new dimension to the concept of an "intelligent spacecraft".
Dr Gordon Keyte from DERA explained the technological developments which offer the opportunity to put high resolution, all-weather radar surveillance capabilities onto satellites of less than 1000 Kg. This capability is currently only to be found on large satellites, such as the 8 ton ENVISAT, with 30 metre long antennas. By careful choice of altitude, frequency and antenna design and the use of ‘spotlight’ techniques, intelligent satellites could provide excellent quality data over smaller areas than their ‘big brothers. The key to exploiting these possibilities lay in tailoring the design of the spacecraft to a particular operation and not to try to make it a "jack of all trades". Also from DERA, Steve Foley explained how his department had pioneered the application of the international standards for packet telecommand and telemetry and successfully demonstrated it on the first STRV mission. Following this success, DERA had developed a secure application of the standard, despite the lack of provision for security in the original design. The secure version is to be demonstrated on the next STRV mission and has potentially wide application in many future programmes. He also explained how the Internet based Space Communications Protocol Standards (SCPS) had been prototyped in combination with the packet T&T to provide high efficiency transparent Internet type communication between space and terrestrial users.
Finally, Commander Richard Blott described DERA's STRV programme and gave some examples of how successful flight demonstration can help the rapid introduction of new technologies into mainstream programmes. The first mission, STRV 1 a&b, were launched in 1994 and have completed over 3 years in orbit during which time one spacecraft onboard computer was reprogrammed to receive and send secure e-mail. Further development of secure versions of this technique on the follow-on mission, STRV 1 c&d, offers potentially dramatic enhancements to the exploitation of space by greater flexibility of access at much reduced cost. Other examples included reductions in the cost of payload electronics by the demonstration of the robustness of terrestrial components in the space environment and the use of terrestrial technology to make smarter satellites and reduce the size and cost of remote sensing instruments. Richard Bavin, DERA Resource Manager for Space Technology, thanked the presenters for a range of interesting topics and expressed the views of many in the audience by acknowledging the very positive note of symposium.