MICHAEL PHELAN / LONDON
Preparation of two-stage design under way in California as Scaled Composites works to win private rocket contest
Scaled Composites is preparing its challenge for the $10 million X-Prize private rocket competition. Its two-stage sub-orbital design comprises a conventional take-off and landing high-altitude aircraft, coupled with an air-launched, rocket-powered second stage and re-entry vehicle.
The first-stage vehicle, dubbed White Knight, is a turbojet-powered high-altitude research aircraft which Mojave, California-based Scaled Composites first flew in August last year. Powered by twin afterburning General Electric J85-GE-5 engines, the 28.4m (93ft)-span aircraft can seat three people and climb to over 53,000ft (16,100m), says the Burt Rutan-led company.
The three-seat SpaceShipOne rocket stage features the same cockpit and systems as the White Knight, including avionics, electrics and environmental control system. After release from the White Knight at 50,000ft, the craft is boosted to an altitude of 100km (62 miles).
SpaceShipOne uses a specially developed hybrid rocket motor that burns nitrous oxide (NO2) and hydroxy-terminated polybutadiene (HTPB), essentially rubber, for safety reasons. Rutan says the HTPB fuel and NO2 oxidiser can be stored safely without the special precautions required for solid rocket fuels or liquid hydrogen and oxygen tanks.
"Starting the motor requires introducing a significant source of heat into the fuel and then the oxidiser. It is a safe and simple alternative to its liquid and solid cousins," he says. Motors are being developed competitively by Environmental Aeroscience of Miami, Florida, and SpaceDev of San Diego, California, and the composite NO2 tank and case/throat/nozzle were developed at Scaled Composites.
Another unusual feature is the second stage's ability to convert to a stable, high-drag shape for atmospheric entry. This configuration allows a "hands-off" re-entry and "greatly reduces aerothermal loads", says Rutan. The cockpit is designed as a "shirt-sleeve" environment, and the vehicle is equipped with three flight-control systems - manual-subsonic, electric-supersonic and a cold-gas re-entry control system.
The SpaceShipOne is flown manually during the entire boost and re-entry phases, and Scaled Composites and FunTech of Orlando, Florida, have developed inertial navigation and GPS systems which provide the pilot with guidance during flight and approach, as well as vehicle health monitoring.
The X-Prize, launched in 1996, offers a cash reward to the first privately financed, built and launched spacecraft able to carry three people to an altitude of 100km, return them to Earth and repeat the flight within two weeks. The flights must be completed before 2005.
Source: Flight International
