Increasing the data volume returned from small satellites

Paper number

IAC-08.B4.6.B7

Author

Mr. Alex da Silva Curiel, Surrey Satellite Technology Ltd., United Kingdom

Year

2008

Abstract

Small satellites are typically highly limited in the amount of power that can be devoted to the payload. This becomes a severe limitation in small Earth Observation missions, where a large volume of data is generated, which must then be transmitted to the ground. Furthermore for operational missions, the spacecraft user would like to use the imaging instrument also in range of their groundstation to retrieve real-time or stored data. 
Traditionally, an isoflux antenna is used to counteract the change of free-space loss throughout an orbital pass to maintain a suitable link margin. However, when the satellite platform is highly agile, the isoflux antenna solution is no longer viable. A typical alternative is to use this problem has been solved by selecting an omni-directional downlink antenna to solve the complex pointing constraints, and increase the orbit average power of the satellite, so that the link margin can be maintained. But this requires higher Transmitter power to maintain a suitable link at low elevations from the groundstation, so increasing the orbit average power and driving This drives up the cost of the satellite.  and Solutions such as data compression or greater efficiencies in the communications system rarely provide the orders of magnitude of improvement demanded in new system designs.
In considering this dilemma SSTL studied how these constraints have been solved on larger spacecraft systems, and has developed a small satellite Antenna Pointing Mechanism (APM) for use on-board its highly agile satellites. This permits SSTL it to use steer a high gain downlink antenna to focus the available on-board energy in a tight beam on the groundstation, whilst leaving the spacecraft free to point a larger Earth Observation instrument. The system provides a greater than 10-fold improvement in the communications link, which can be used to increase the date rate, or reduce the amount of power required for downlinking. The cost of using the mechanism is more than offset by the savings that can be made, and has been carefully considered in the trade between mechanically and electrically steered antenna. The APM is complemented by a high capacity solid state data recorder, and high rate X-band Transmitter modulator, amplifier and antenna to provide a cost effective yet highly capable downlink chain. 
The paper will describe the APM design trades, its qualification, and the mission on which the first two units will be flown. The paper will also provide an overview of the complete downlink chain, and show how such a chain can provide a far superior solution in terms of mass, power and cost compared with a more traditional approach.

Abstract document

IAC-08.B4.6.B7.pdf

Manuscript document

IAC-08.B4.6.B7.pdf (🔒 authorized access only).

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