SSTL is also engaged in the development of its own spacecraft-propulsion system. The company has recognised that the lack of an on-board propulsion system has prevented it from exploiting fully the potential of its micro/minisatellite fleet.
The company has certainly pioneered the use of small craft to conduct effective communications, Earth observation and science missions. With the introduction of the microsatellite for operational, customised missions, a cost-effective propulsion system for orbital manoeuvring, orbital maintenance and attitude control is regarded as essential.
These capabilities can be provided by several off-the-shelf propulsion systems, but these may not be appropriate for the small satellite mission in terms of size and cost, which is "prohibitive" for a small customer, says SSTL. The company decided to develop its own system - a restartable, hybrid 400N-thrust engine which runs on solid-polyethylene fuel and liquid hydrogen-peroxide oxidiser. This will be demonstrated on the UoSAT 12 flight.
SSTL - with the aid of Royal Ordnance - conducted the first firing of the motor just seven months after proof-of-concept-phase start-up and at a cost of less than $20,000. US Air Force interest has resulted in a small research contract. The success of these tests allowed the final design of the microsatellite to be completed.
SSTL is also developing and demonstrating another form of on-orbit propulsion, the water resistojet, for orbit stationkeeping and maintenance rather than orbital manoeuvring.
The resistojet is an electrothermal thruster where electrical energy is used to heat the working fluid directly. The hot gas is expanded through convergent/divergent nozzles to provide high exhaust velocities. The advantage over any other fluid of using water is its high density, low mass and inherent safety.
SSTL has developed and demonstrated a Mark 1 thruster and the 0.05N to 0.5N-thrust Mark 2 model will be flown aboard the UoSAT 12.
Source: Flight International
