MX-774

MX-774
Type	Prototype Intercontinental Ballistic Missile
Place of origin	United States
Production history
Designer	Consolidated-Vultee
Designed	1946
No. built	3
Specifications
Weight	1,205 pounds (547 kg) empty, 4,090 pounds (1,860 kg) full,
Length	31.5 feet (9.6 m)
Width	6 feet 10 inches (2.08 m)
Diameter	30 inches (760 mm)
Engine	Four XLR35-RM-1 engines 2,000 pounds-force (8,900 N) each
Propellant	Alcohol fuel
Operational range	8,000 miles (13,000 km)

The RTV-A-2 Hiroc (High-altitude Rocket) was the United States' first attempt at an intercontinental ballistic missile (ICBM). The project was cancelled in 1947 and only three were tested but several features of the rocket had a lasting effect. Gimballed engines were used for guidance and propulsion, internal gas pressure was used to support the frame and the nose cap was separable, which were also used on Atlas missiles.

The Hiroc missiles were 31.5 feet (9.6 m) long, had a finspan of 6 feet 10 inches (2.08 m), a diameter of 30 inches (760 mm) an empty weight of 1,205 pounds (547 kg) and a gross liftoff weight (GLOW) of 4,090 pounds (1,860 kg), to reach 8,000 miles (13,000 km) with a 500 pounds (230 kg) payload. The missiles propulsion system consisted of four XLR35-RM-1 engines, built by Reaction Motors Inc., which produced 2,000 pounds-force (8,900 N) each and could independently swivel up to ten degrees either direction. The Hiroc missiles did not have separate tanks for its fuel and oxidizer, which were instead in one tank separated by a bulkhead. The frame of the rocket was supported by the pressure of the gas inside the tank, which would be either propellants when used, or inert gasses when stored. Gas pressure support reduced the empty weight but made the missiles very fragile and dependent on being pressurized continuously. The nose cone, which contains the ordnance was separated from the rocket, which made the rocket lighter as only the nose cone and its ordinance had to be able to survive re-entry, rather than the rocket. The Hiroc had a specific impulse of 210 s at sea level. The unique design of the Hiroc missiles would go on to inspire the Atlas rockets.

In April 1946, Convair received a 1.9 million dollar contract from the US Government to build and test ten MX-774 Hirocs. Funding was cancelled in June 1947 but Convair used the remaining contract funding to launch three of the rockets, which were renamed RTV-A-2 Hiroc. The tests took place at White Sands Proving Ground. The three tests took place on 13 July 1947, 27 September, and 2 December. These tests validated the concept of using gimballed engines for propulsion and guidance.