in april 1986 mcdonnell douglas, rockwell international, and general dynamics were awarded contracts (each no more than $35 m) to develop technology for a hypersonic air-breathing ssto vehicle/airframe. rocketdyne and pratt & whitney were each awarded contracts of $175 m to develop engines/propulsion. the airframe contractors would compete and two or three would be eliminated after a year. the plan was that 42 months later (end of 1989), contracts would be awarded to build the flight demonstrator vehicle.