TOPSAT: A HIGH PERFORMANCE SMALL SATELLITE FOR EARTH OBSERVATION

摘要

The UK's "TopSat" satellite was launched on 27th October 2005, and has since undertaken a remote sensing programme providing high resolution optical imagery for a wide range of applications. The TopSat programme has been used to demonstrate the ability to build and operate a low-cost optical small-satellite capable of generating timely high quality imagery. The system combines a responsive tasking process with a rapid down-linking capability - giving users the ability to receive near-real time imagery of commercial quality. The satellite, built by a QinetiQ-led consortium, of mass 108kg, produces panchromatic imagery (17×17km) with a spatial resolution of 2.8m, and multi-spectral imagery (12×18km) with 5.6m resolution. During routine operations, imagery is downloaded to QinetiQ's ground station at West Preugh in Scotland; however the system also operates with a mobile ground station called RAPIDS, consisting of a 2.7m receiving dish towed by a Land Rover. The spacecraft is operated from the Payload Operations Centre at Farnborough in the UK, often working in close communication with users to meet specialised requirements. Remarkably, the spacecraft (and operations) were developed, built and launched for under $25M, resulting in a world leading performance to cost ratio. TopSat has now exceeded its design mission lifetime and has built up a large archive of imagery from around the world for use in a wide range of applications including disaster monitoring, cartographic updates, civil and security operations planning. TopSat's leading performance-to-cost ratio and rapid end-to-end timeliness capability make it ideally suited to work within tight timescales; whether for disaster relief, news gathering or security applications. Typical image turnaround is a few days and the system has been used to demonstrate the tasking, imaging, down-linking and image processing of a scene within an hour. By virtue of its small size and low cost, TopSat has opened the way for affordable constellations capable of launch on a single small launch vehicle. A constellation provides greatly enhanced image responsiveness and thereby overcomes some of the fundamental limitations of space-based systems. The programme, originally funded by the British National Space Centre (BNSC) and the UK Ministry of Defence, has since become a commercial venture between the TopSat Consortium partners (QinetiQ, RAL, SSTL and Infoterra). This paper will discuss the Consortium's activities over the past year, focussing on demonstrations of the utility of responsive small imaging satellites through experiments in rapid end-to-end timeliness.