Posted: Sun, Jul 8, 2018, 9:41 AM ET (1341 GMT)
A shuttle-era engine is undergoing a series of daily test firings to demonstrate its suitability for a DARPA spaceplane program. Aerojet Rocketdyne's AR-22, a lightly modified version of the Space Shuttle Main Engine, is being fired once a day over the course of 10 days, starting last week. Those tests are intended to show that the engine can be turned around for daily flights of Boeing's Phantom Express vehicle, being developed under DARPA's Experimental Spaceplane program. That program has a goal of performing 10 flights in 10 days of the reusable lower stage, which takes off vertically and glides to a runway landing. Phantom Express, equipped with an expendable upper stage, is intended to be able to place medium-class payloads into orbit at prices far lower than current expendable launch vehicles.

Related Links:

•  SpaceNews article
•  AP article