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AR-22 rocket engine firing
Aerojet Rocketdyne’s AR-22 rocket engine fires during a test at NASA’s Stennis Space Center in Mississippi. (NASA / DARPA Photo)

A rocket engine built from spare space shuttle parts — and the team behind the engine — passed a grueling 10-day, 10-firing test that sets the stage for Boeing’s Phantom Express military space plane.

“We scored a perfect 10 last week,” Jeff Haynes, Aerojet Rocketdyne’s program manager for the AR-22 engine, told reporters today during a teleconference.

The hydrogen-fueled AR-22 is largely based on the RS-25 engine that was used on the space shuttle and will be used on NASA’s heavy-lift Space Launch System. “We’ve upgraded the ‘brain’ for this derivative mission,” using an advanced controller, Haynes said.

Aerojet, Boeing and the Pentagon’s Defense Advanced Research Projects Agency, or DARPA, set up the 240-hour test between June 26 and July 6 to see whether the AR-22 could be turned around rapidly enough for a 100-second, full-throttle firing every day. The bottom line? It can.

“We had 68 minutes to spare when we finished the last test,” Haynes said.

Along the way, the team had to deal with two direct lightning strikes that damaged the test facility at NASA’s Stennis Space Center in Mississippi. Engineers also had to work out a procedure to get rid of the moisture that gathered in the engine during firings.

“Trying to run the engine again without drying that out would lead to catastrophic events,” Haynes said.

At first, the procedure took about 17 hours, but they eventually got the time down to as little as six hours. During the shuttle program, a similar process took days to accomplish, Haynes said.

Thanks to the successful test, the Phantom Express program — also known as the Experimental Spaceplane or XS-1 — is on track for an initial demonstration flight in 2021, said Steve Johnston, director of launch at Boeing Phantom Works.

Scott Wierzbanowski, DARPA’s program manager for the Experimental Spaceplane, said the two-stage launch system is being designed for 10 liftoffs in 10 days. After each launch, the reusable first-stage booster would glide to an airplane-like landing.

Phantom Express should be capable of delivering 3,000 pounds of payload to low Earth orbit at a cost of less than $5 million a flight. Those performance levels represent a “sweet spot” for military as well as commercial applications, Wierzbanowski said.

Boeing’s Johnston said the specifications for the Phantom Express plane are going through critical design review, leading up to the start of assembly in mid-2019.

“A lot of our design philosophies and design guidelines are actually derived from the commercial airplane business,” he said. “The materials system that we’re using is actually the materials system that was originally developed for application on the all-composite 787.”

The liquid-oxygen tank already has been fabricated at Boeing’s Advanced Developmental Composite Facility in the Seattle area. “It went really well. … We have some additional outfitting to do to that tank,” Johnston said.

The design of the plane’s upper stage is still in flux, and the launch site for the first demonstration flight in 2021 has not yet been selected. That initial suborbital flight will test only the first-stage booster, Johnston said.

DARPA is providing up to $146 million for the project, with Boeing and Aerojet kicking in an additional unspecified amount for development.

AR-22 rocket engine inspection
Technicians inspect the AR-22 rocket engine after a hot-fire test. (Aerojet Rocketdyne Photo)

Haynes said the lessons learned from the 10-day engine test could be applied not only to the Phantom Express, but also to Aerojet’s work on the RS-25 engines for the Space Launch System. For example, the SLS could benefit from a sensor-based performance-monitoring system that was tested on the AR-22, known as the Advanced Anomaly Command and Control Center, or AC3.

“We actually tricked the engine to thinking it was experiencing a red-line condition, which under the shuttle program would have been an immediate shutdown of the engine,” Haynes said. “We allowed our software to throttle down the engine automatically, assess the situation and then do a stepwise recovery of the thrust profile in a matter of seconds.”

Aerojet is pioneering a new generation of engineering for Phantom Express and the Space Launch System — with the aid of a new generation of engineers, Haynes said.

“We have experienced engineers that really cut their teeth on the shuttle program,” he said. “And we have a large amount of new engineers now that are able to be mentored and trained through the process of this highly aggressive program that we just did through the last two weeks.”

Phantom Express XS-1 space plane
An artist’s conception shows Boeing’s Phantom Express XS-1 space plane in flight. (Boeing Illustration)

Phantom Express by the numbers:

Length: 100 feet

Wingspan: 62 feet

Weight at liftoff, fully fueled: 240,000 pounds

AR-22 engine liftoff thrust: More than 375,000 pounds

AR-22 propellants: Liquid hydrogen, liquid oxygen

Maximum speed: Mach 10 (7,600 mph)

Sources: Boeing, Aerojet Rocketdyne

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