Martin X-23
From the placard:
The PRIME (Precision Recovery Including Maneuvering Entry) project ws
the second part of the START (Spacecraft Technology and Advanced
Reentry Test) program. It had the dual objective of testing advances
in space hardware and further exploring the development of manned and
unmanned lifting body vehicles. Four XV-5D [ed. note: also known
as the X-23] vehicles were built by the Martin Company to fulfill
the objectives of the PRIME program. Outside earth's atmosphere the
SV-5D was maneuvered by the release of high pressure nitrogen through
jet thrusters. When the craft re-entered the atmosphere its control
system automatically swithced to airplane-type flaps for pitch and
roll control.
On a typical flight, the unmanned XV-5D was launched by an Atlas
booster from Vandenburg AFB, California. At the high point in its
flight path, the Atlas pitched downward while its rocket continued
accelerating it to speeds nearly as great as those of the spacecraft
re-entering the earth's atmosphere. The lifting body's inertial
guidance system directed it to a preselected recover point. Three
PRIME test flights were made, the first on December 21, 1966, and the
last on April 19, 1967. A scheduled fourth flight was cancelled due to
the successes of the previous tests.
