X-33's innovative aerospike engine undergoes a similar firing test on February 3. Photo: NASA/SSC

The innovative aerospike engine that will power the X-33 Advanced Technology Demonstrator successfully completed its 11th of 14 scheduled single-engine hot-fire tests March 22 at NASA's Stennis Space Center, Miss. The test -- the longest duration test to date -- ran for a planned 220 seconds.

The 220-second duration simulates the longest predicted engine burn time the X-33 will experience on a flight test. The test also marked the first successful demonstration of a 30 percent per second throttling rate from the 100 percent to 72 percent engine power levels.

A cold helium flow test also was conducted during the March 22 test. All test objectives appear to have been met, pending final data review. Post-test inspections are in workunder way.

The previous engine test -- test No. 10 -- was had been scheduled for 220 seconds but it it was shut down prematurely at 75.44 seconds due to missing a when a fuel pump discharge pressure qualification limit on fuel pump discharge pressurewas missed in new mixture ratio control software. The software was adjusted for the March 22 test, and a preliminary review of data indicates the new mixture ratio control software is working well.

All nine tests prior to the shortened test, and test No. 11, achieved their full planned durations. All three of tThe final three single-engine aerospike tests scheduled at NASA Stennis are planned to be 250-seconds in duration. The next test is schedule for April 3 and would mark a turn-around between tests of just eight business days.

The XRS-2200 engine was developed and assembled by Boeing Rocketdyne Propulsion & Power, Canoga Park, Calif. The engine will power the X-33, a half-scale, sub-orbital technology demonstrator of Lockheed Martin's proposed, commercial reusable launch vehicle called VentureStarTM.

The X-33 is being developed in partnership with NASA and Lockheed Martin Aeronautics Company, Palmdale, Calif. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the X-33 program for NASA.