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Forty-five years ago this month, the United States Air Force successfully flew and recovered the third and final Project PRIME Flight Test Vehicle (FTV-3).  PRIME stood for Precision Recovery Including Maneuvering Entry.  The ability to generate aerodynamic lift allows a reentry vehicle to maneuver along the endoatmospheric portion of its entry flight path.   The main goal of Project PRIME was to flight test a hypersonic, maneuvering lifting body vehicle designated as the USAF/Martin SV-5D.  Configured with 3-axis aerodynamic and reaction controls, the SV-5D weighed 892 lb and measured 6.7 ft, 4.0 ft and 2.8 ft in length, span and height, respectively.  Thermal protection was provided by a then-novel charring ablator material.  The SV-5D was an autonomous vehicle and thus had its own guidance, navigation and control system.  On Wednesday, 19 April 1967, PRIME FTV-3 was launched by an Atlas booster from Vandenberg Air Force Base, California.  The vehicle’s trajectory took it toward Kwajalein Missile Range (KMR) located 4,400 nm to the west in the Marshall Islands.  FTV-3 performed a variety of controlled maneuvers during entry in which a maximum crossrange of 710 nm was achieved.  The vehicle modulated crossrange by banking as much as 64 degrees while simultaneously pulling angles-of-attack as high as 57 degrees to achieve the required lift vector.  Indeed, this very same crossrange maneuvering strategy would be used by the Space Shuttle Orbiter a decade and a half later.  FTV-3 deployed a drogue parachute as it passed through Mach 2 at 100,000 feet. Main parachute deployment then occurred in the vicinity of 50,000 feet.  As the vehicle-parachute combination neared an altitude of 12,000 feet, the crew of a USAF/Lockheed JC-130B Hercules then executed the only successful aerial recovery of a PRIME flight test vehicle.  A planned fourth flight was cancelled due to the great success achieved in the preceding trio of PRIME flight tests.  As a final note, FTV-3 was subsequently returned to the contractor for post-flight inspection and testing.  Today, the recovered FTV-3 airframe is on public display at the United States Air Force Museum in Dayton, Ohio.

Posted in Aerospace, History

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