GRAHAM WARWICK / WASHINGTON DC
Mach 4 aircraft will use mass injection pre-compressor cooling system to boost thrust for climb out of atmosphere
Scaled Composites is working on a Mach 4 aircraft capable of leaving the atmosphere and launching a low-cost rocket. The Burt Rutan-led company is designing the aircraft for Space Launch, the company awarded a US Defense Advanced Research Projects Agency (DARPA) contract to demonstrate the Responsive Access Small Cargo Affordable Launch (RASCAL) system.
RASCAL will launch a 115kg (250lb) payload into a 500km sun-synchronous orbit, or 180kg into a 28.5°-inclined orbit, for $750,000, with a 24h mission turnaround time and a 1h scramble capability from any 1,500m (5,000ft) coastal runway, says programme manager Preston Carter. The system will also be able to release ballistic payloads.
A blend of reusable and expendable components will reduce cost. The reusable first stage is a manned aircraft powered by four Pratt & Whitney F100 afterburning engines with mass injection pre-compressor cooling (MIPCC). The Rutan-designed MIPCC-Powered Vehicle (MPV) is a 36,300kg gross-weight aircraft, 27.1m long with a 27.4m-span delta wing. A payload bay houses the 7,300kg Expendable Rocket Vehicle (ERV), which has a hybrid first stage, solid-propellant second stage, a head-end module housing avionics and thrusters, and the payload. The ERV is being designed by Space Launch and ATK.
Pre-compressor cooling was ground tested in the 1950s for high-altitude interceptors, but development was discontinued, says Preston. Injecting water and liquid oxygen into the inlet ducts to cool and densify the airflow will boost thrust from the unmodified engines by a factor of two or three, and give the MPV a thrust-to-weight ratio close to 2:1. "MIPCC lowers temperatures by hundreds of degrees at higher Mach numbers, and convinces an engine flying at Mach 3 and 100,000ft it is flying at M1.2 and 20,000ft," he says.
MIPCC will "hot rod" the F100s to power the MPV as it zoom climbs to Mach 4 and 120,000ft, where the engines will shut down and reaction controls take over. The ERV will be deployed at 190,000ft, and the MPV will coast up to 200,000ft before re-entering, restarting the engines and returning to land. The mainly composite airframe will use titanium and steel in high-temperature areas and be covered in an insulating ablative material, Preston says.
Phase 2, now under way, includes windtunnel, inlet, MIPCC engine and rocket ground testing. If RASCAL reaches Phase 3, flight testing would begin in 2005, with two orbital launches in 2006. The technology demonstrator would have a residual operational capability.
Source: Flight International
