WASHINGTON — NASA wrapped up a series of three linear aerospike engine tests with a 90-second tandem firing of a pair of engines the evening of Aug. 6 at Stennis Space Center near Bay St. Louis, Miss.

The experimental linear aerospike engines were built by Boeing’s Rocketdyne Power and Propulsion division for the X-33 resuable launch vehicle prototype program, which NASA cancelled in March.

The engine tests, which were focused on the performance of the engines’ electromechanical actuators, were funded under NASA’s Space Launch Initiative, a $4.8 billion reusable launch vehicle technology development effort. Both engines were fired as a single propulsion unit during all three tests.

Stennis spokesman Paul Foerman said the third and final test commenced at 7:58 p.m. local time. Originally the engines were to burn for 100 seconds, but NASA technicians determined that a 90-second test was all that was necessary to achieve test objectives.

"There were no anomalies," Foerman said. "It looks like it was a good test."

What happens next with the linear aerospike engines, along with the rest of the X-33 flight hardware, is still not clear. The U.S. Air Force has expressed an interest in taking over the orphaned program, but has made no formal commitment to do so.

NASA spokesman James Cast said the U.S. space agency continues to discuss the X-33 program’s future with the Air Force, but has made no additional financial commitment to the program.

Meanwhile, NASA and Lockheed Martin — the agency’s partner in the X-33 endeavor — continue to negotiate the financial terms of the $1.3 billion program’s cancellation.