CINCINNATI — A government-industry team announced July 10 they successfully completed a series of 10 test firings over 10 days of a shuttle-era engine intended for use on a reusable suborbital spaceplane.

In a teleconference with reporters, officials with Aerojet Rocketdyne, Boeing and the Defense Advanced Research Projects Agency said the series of static-fire tests of the AR-22 engine at NASA’s Stennis Space Center, which concluded July 6, demonstrated the rapid turnaround needed for the engine to power a suborbital spaceplane intended to demonstrate responsive launch capabilities.

“It was a significant go/no-go milestone for us in order for us to move forward with the program,” said Scott Wierzbanowski, program manager of DARPA’s Experimental Spaceplane program. “We shattered this idea that these types of engines can’t be used in a very operable and aircraft-like way.”

The goal of the test program was to perform 10 100-second firings of the AR-22, a variant of the Space Shuttle Main Engine, in 240 hours. The tenth and final test was completed with 68 minutes to spare, said Jeff Haynes, AR-22 program manager at Aerojet Rocketdyne.

The rapid turnaround — as little as 17 hours between some tests — created some challenges. The biggest, Haynes said, is dealing with the moisture generated within the engine during firings. “Trying to run the engine again without drying that out would lead to catastrophic events,” he said. Typically, drying the engine after a test takes about 17 hours, but the engine test team found ways to reduce that time to as little as six hours.

Engineers also streamlined the inspections between engine firings. “These were reduced inspections from what the shuttle program had accomplished,” he said, based on the experience from the shuttle program. The engine also had a new health management system that, in an additional test, diagnosed a simulated problem with the engine and resolved it without having to abort the firing.

Boeing selected the AR-22 for its Phantom Express reusable spaceplane, which won the DARPA Experimental Spaceplane contract last year. The original DARPA concept for the program calls for being able to do 10 flights in 10 days, flying at speeds up to Mach 10. Phantom Express would take off vertically and, after deploying an expendable upper stage, glide back to a runway landing.

“We are relying on Aerojet Rocketdyne’s AR-22 engine to make this possible, to provide the performance that we need to support the system,” said Steve Johnston, director of launch at Boeing Phantom Works. “The series of tests that we just completed last week was a huge milestone in terms of burning down risks.”

Johnston said that the tests reassured him the spaceplane could be turned around and launched again within 24 hours. He specifically mentioned the efforts to reduce the engine drying time between launches. “That was the single biggest step to meet the vehicle-level turnaround. So this gives us a lot of confidence,” he said.