Two unique engines designed to propel America's X-33 into high-speed, suborbital flight in 2003 have been mounted side by side in a Mississippi test stand for qualification firings, now slated for later this year.

The two linear aerospike engines mounted on a test stand at NASA's Stennis Space Center, Miss. The twin engines, built to power the X-33 rocket plane, will undergo test fires beginning later this year. Photo: NASA

At NASA's Stennis Space Center, Miss., tandem test firings of X-33's Linear Aerospike XRS-2200 engines will begin with short bursts and will eventually lead to full firings for durations needed to send the unpiloted vehicle from a launch pad in California to landings in either Utah or Montana.

X-33, being developed under a cooperative agreement between NASA and Lockheed Martin, is a half-scale prototype of a commercially developed and operated, reusable launch vehicle of the future, and is designed to demonstrate new, reusable single-stage-to-orbit technologies. One goal of the project is to provide safe, reliable and affordable access to space.

Fourteen single-engine test firings of an earlier version the unique Aerospike engine, developed by the Rocketdyne Propulsion and Power Unit of the Boeing Company, were successfully completed earlier this year.

Another view of the engines on test stand. Photo: NASA

The difference between the linear Aerospike engine and conventional rocket engines is the shape of the nozzle. Unlike conventional rocket engines that use a bell nozzle to constrict expanding gases, the Aerospike nozzle is V-shaped and called a ramp.

The hot gases are shot from chambers along the outside of the ramp's surface. This unusual design allows the engine to be more efficient and effective than today's rocket engines.

At least nine test firings of the twin flight engines are planned at Stennis before they are delivered to Lockheed Martin's X-33 assembly facility in Palmdale, Calif.

The X-33 Program is managed by NASA's Marshall Space Flight Center in Huntsville, Ala.