 The DOD reported that Transtage could support all defense needs, but could not meet NASA's scientific requirements, the IUS could support most defense needs and some science missions, while the Centaur could meet all needs of both the Air Force and NASA.Development began on both the Centaur and the IUS, and a second stage was added to the IUS design which could be used either as an apogee kick motor for inserting payloads directly into geostationary orbit or to increase the payload mass brought to escape velocity.Development of the Shuttle-Centaur was halted after the Challenger disaster, and the Interim Upper Stage became the Inertial Upper Stage.