PRIME (Precision Recovery Including Maneuvering Entry) is the second part of the United States Air Force START project on lifting bodies, following ASSET. It involved the development and reentry testing of the SV-5D, also known as the X-23A, a 2-meter-long, 1-meter-wide subscale version of the lifting body configuration used in the X-24A manned aerodynamic test aircraft. Three missions were flown in 1966-67, each beginning with a launch by an Atlas booster from Vandenberg Air Force Base. Outside Earth's atmosphere, the SV-5D maneuvered using nitrogen-gas thrusters then reentered and descended to a controlled landing using an inertial guidance system and airplane-type flaps for pitch and roll control.