As the Defense Advanced Research Project Agency's Experimental Spaceplane program approaches its first subsystem-level critical design review next month, the program's propulsion provider last week completed a key testing demonstration, proving the engine can support the reusable spaceplane's anticipated fast-paced operational tempo. Aerojet Rocketdyne's AR-22 engine will power the spacecraft, which is being built by Boeing and is slated for first flight in 2021. The two companies and DARPA hosted a media briefing July 10, and Aerojet program manager Jeff...