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The hydrogen-fueled PGA will produce 200,000 pounds of liftoff thrust. “When you try to do something like single stage to orbit, or in our case air launch, you really have to have hydrogen performance to make it happen,” Jeff Thornburg, Stratolaunch’s vice president of propulsion engineering, told Aviation Week.
Stratolaunch says that 85 percent of the manufacturing process will take advantage of additive-manufacturing techniques, also known as 3-D printing. That’s aimed at reducing the cost of engine production. “The propulsion team is currently in the process of manufacturing and testing prototype subscale and full-scale hardware,” Stratolaunch says. “The team has completed ignitor development, with injector testing currently underway. After this is completed, the team will perform a full-scale preburner test by the end of 2018.”
The engine is being designed to power the rockets and manned ferry that they also plan to build to be launched from the bottom of their giant airplane Roc.
It is clear now that they could not find anyone else willing to build these upper stages, and are now building them themselves. This means that SpaceX, with its Big Falcon Rocket, is now not the only company building a completely reusable system for gaining access to space.