PGA preburner hot-fire test
The preburner for Stratolaunch’s PGA rocket engine blazes during a hot-fire test. (Stratolaunch via Twitter)

Chalk up another milestone for Stratolaunch Systems’ rocket engine development effort: The Seattle-based space company founded by late Microsoft co-founder Paul Allen says it ramped up the preburner for its PGA rocket engine to full power this week during hot-fire tests.

Stratolaunch’s 3D-printed preburner, a key component that typically begins a rocket engine’s combustion process, had its first hot firing less than a month ago at NASA’s Stennis Space Center in Mississippi. And just a year ago, the hardware was merely a twinkle in the eye of Stratolaunch’s engineers.

“Per public records, this is the fastest preburner development in U.S. history,” Hanna Steplewska Kubiak, Stratolaunch’s vice president of business development,  tweeted.

Friday’s progress report suggests that Stratolaunch is moving along quickly with development of the PGA, which takes its name from Paul G. Allen’s initials. (The same initials are emblazoned on a patch that football players on the Allen-owned Seattle Seahawks have been wearing on their uniforms since Allen’s death in October.)

The firing shown in Stratolaunch’s video clip lasted 19.6 seconds, and the duration of the burn is likely to be increased as the tests continue. Other components will have to be tested as well, eventually leading to full-scale hot-fire tests of the complete rocket engine.

When completed, the hydrogen-oxygen engine should produce 200,000 pounds of liftoff thrust for a wide range of launch vehicles that Stratolaunch is developing in-house. The first in-house rocket, known as the Medium Launch Vehicle or MLV, is due to fly in 2022.

Stratolaunch is also working on the world’s largest airplane at its facility at California’s Mojave Air and Space Port. Flight tests of the twin-fuselage, 385-foot-wingspan plane are expected to begin soon, with the aim of using it as a platform for air-launched rockets by as soon as 2020. The first launches would make use of Northrop Grumman’s Pegasus XL rockets rather than the PGA-powered MLV.

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