In 1945 the U.S. Army Air Force awarded Consolidated-Vultee project MX-774, which was to lead to a long-range ballistic missile. The project included proving technologies using a test vehicle, the Hiroc (High-Altitude Rocket) . MX-774 was cancelled in June 1947, but Convair was allowed to complete and fly three test vehicles using available funds. A Reaction Motors XLR35-RM-1 four-chamber liquid-propellant rocket motor was fitted to the rocket's cylindrical body. Four fixed stabilizing fins provided stability. New technologies demonstrated gimballed rocket nozzles, a separable nose cone, and the balloon internal pressure stabilized flight structure. The missile's skin was very thin, and was inflated by internal pressure like a balloon. Three Hiroc's were flown in July to December 1948. None were entirely successful. However the know-how obtained in designing and building the missiles would be the starting point for the Atlas ICBM just a few years later.
Historical Essay © Andreas Parsch
Convair RTV-A-2 Hiroc
Among the various guided missile studies initiated by the U.S. Army Air Force in 1945 was Consolidated-Vultee's project MX-774, which was about supersonic surface-to-surface missiles. After the development contracts for cruise-type winged missiles went to Martin (MX-771, SSM-A-1-TM-61 Matador) and Northrop (MX-775, SSM-A-3-SM-62 Snark), Convair was awarded a contract to develop and test a ballistic research missile under project MX-774. The effort was named Hiroc (High-Altitude Rocket) and the vehicle received the designation RTV-A-2 in 1947. However, the program was formally cancelled in June 1947, but Convair was allowed to complete and fly three test vehicles using available funds.
The RTV-A-2 was powered by a Reaction Motors XLR35-RM-1 four-chamber liquid-fueled rocket motor, and had a cylindrical body with four fixed stabilizing fins. The Hiroc pioneered several new design techniques which would later be used in the SM-65-HGM-16 Atlas. It featured a gimballed rocket nozzle to steer the vehicle by thrust-vectoring instead of weight- and drag-increasing control fins, and had a separable nose cone for the payload. The most radical feature of the RTV-A-2 was its internal pressure stabilized flight structure. The missile's skin was very thin, and was inflated by internal pressure like a balloon. This significantly reduced the empty weight of the vehicle. However, it also made the missile rather fragile, because a single hole in the skin would lead to the collapse of the whole structure, just like a limp balloon. The RTV-A-2 used telemetry to transmit flight data to the ground, and the nose cone was designed to be recoverable by parachute.
The first RTV-A-2 flew in July 1948, followed by the other two rockets in September and December that year. All three flights were only partially successful (mainly because of engine failures), but helped a lot to validate the new design concepts.Specifications
Note: Data given by several sources show slight variations. Figures given below may therefore be inaccurate!
Data for RTV-A-2:
|Length||9.63 m (31 ft 7 in)|
|Finspan||2.08 m (6 ft 10 in)|
|Diameter||76 cm (30 in)|
|Weight||1860 kg (4100 lb)|
|Speed||3200 km-h (2000 mph)|
|Ceiling||> 65 km (40 miles)|
|Propulsion||Reaction Motors XLR35-RM-1 liquid-fueled rocket; 35.5 kN (8000 lb)|
 Jay Miller: "The X-Planes X-1 to X-45", Midland Publishing, 2001
 Frederick I. Ordway III, Ronald C. Wakeford: "International Missile and Spacecraft Guide", McGraw-Hill, 1960
Status: Cancelled 1947.