Guy Norris/LOS ANGELES
Development problems with the linear aerospike engine have forced Lockheed Martin to delay the first flight of the X-33 reusable launch vehicle (RLV) prototype by four months to December 1999. Longer range tests will now not be conducted until 2001.
Despite the delay, Lockheed Martin says it will still deliver the engineless airframe to the launch site at Edwards AFB, California, by the original July 1999 target date. The delay is expected to add around $36 million in extra costs, but Lockheed Martin, which is substantially over budget on the X-33, says Boeing's Rocketdyne division will meet the bill.
"It is not going to add cost to Lockheed Martin," says the company's X-33 programme manager, Jerry Rising. "The added cost is to Boeing's Rocketdyne effort and Lockheed Martin is not going to pick up that. We have a co-operative agreement, and every teammate has its task and a budget to meet that task."
The problems are related to the milling process used to form the copper alloy plates which line the "V"-shaped ramp of the aerospike rocket. The ramp is actually the rocket's nozzle which, in a conventional motor, is normally bell shaped. In the aerospike nozzle, the hot combustion gases expand on the outside surface, or ramp.
The engine problems are tied specifically to the development of a milling process which produces grooves in the plates, which are then braced together to provide cooling channels for liquid hydrogen. The remaining elements of the engine development are going well, says Rocketdyne, which conducted the first powerpack test with a successful 2.81s firing in October. Each of the two XRS-2200 engines on the X-33 will have a series of 20 combustion chambers, with 10 aligned along the forward end of each nozzle ramp. The prototype version will generate 206,400lb thrust (918kN) at sea level while the equivalent full-scale engine in a production RLV will be rated at 431,000lb.
"Hot fire" tests of a subscale linear aerospike engine mounted on the back of a Lockheed SR-71 have been tentatively scheduled to be carried out in December.
Source: Flight International
