Ian Sheppard/LONDON

NASA and Rocketdyne have completed the preliminary design and initial testing for the engine for Lockheed Martin's X-33 Venture Star half-scale technology-demonstrator launch vehicle, the first flight of which is scheduled for March 1999.

It is hoped that the $5 billion development of a full-scale re-usable launch vehicle will get the go-ahead by the end of the century, for it to be fully operational as a Shuttle replacement by 2005.

The XRS-2200 is a linear-aerospike engine, the full-scale version of which will be known as the RS-2200. The nozzle shape accounts for the "aerospike", as it is a truncated V-shaped ramp where the combustion gases expand on the outside of the V to allow the shape of the unconstrained plume to self-optimise, changing naturally with altitude. The result is a far more efficient "burn", and greatly reduced base drag compared with that of an equivalent vehicle using bell-shaped nozzles. The truncated base allows exhaust gases to add to the thrust, rather than being recirculated, as in the Space Shuttle's main engine, thus further increasing efficiency.

Initial tests successfully proved the operation of the combustion cells which will line the top of the ramp. The cells also allow the craft to be steered without gimballing the engine or using secondary thrusters.

Full testing of the 917kN (206,000lb)-thrust XRS-2200 engine is scheduled to begin early in 1998 at NASA's Stennis Space Center in Mississippi. Each full-scale Venture Star will have two engines rated at 1,807kN thrust at sea level.

It is believed that the Venture Star will be flight-tested from a high-altitude location, such as White Sands, New Mexico.

Source: Flight International