Blue Origin said Sunday that it lost a set of powerpack hardware for its BE-4 engine during a ground test mishap, dealing at least a minor setback to the development of a powerful U.S.-made propulsion system that United Launch Alliance says is the leading candidate to power the first stage of its next-generation Vulcan rocket.

NASA’s four Magnetospheric Multiscale mission spacecraft were encapsulated Feb. 23 in the United Launch Alliance Atlas 5 rocket’s nose cone at the commercial Astrotech processing campus in Titusville. Delivery of the payload to the Atlas 5 assembly building for mating occurred on Friday, Feb. 27.

U.S. Air Force officials signed off Monday on a plan for SpaceX and United Launch Alliance, rivals in the launch services market, to fire off Falcon 9 and Atlas 5 rockets from neighboring launch pads at Cape Canaveral on Tuesday evening and Thursday morning.