Redstone version
Redstone Mercury-Redstone Launch Vehicle
The Mercury-Redstone was America's first crewed launch vehicle: six sub-orbital flights between November 1960 and July 1961, the last two carrying Alan Shepard and Gus Grissom. It was built on the stretched Jupiter-C first stage but used the operational Redstone's A-7 engine, with some eight hundred changes made to render it safe for a passenger.
- November 21, 1960
- First launch
- 347 kN
- Thrust
- No
- Reusable
History
Why the Redstone
NASA wanted the most seasoned booster in the American inventory for its sub-orbital flights, and the Redstone qualified: flying since 1953, with a long record of successful tests behind it. Thrust was the obstacle. A production missile could not push a Mercury capsule onto the intended ballistic trajectory, so the Jupiter-C first stage, with its lengthened tanks, was taken as the baseline. The engine came from the opposite direction: the Army was phasing out the Jupiter-C powerplant, so designers took the A-7 from the latest military Redstone instead.
Giving up Hydyne
The Jupiter-C burned Hydyne, more energetic than ethyl alcohol but considerably more toxic — an unacceptable hazard in a pad emergency with an astronaut aboard. The Mercury-Redstone went back to alcohol and water with liquid oxygen, which turned the long tanks from an improvement into a requirement. The longer burn that followed forced NASA to demand higher-grade graphite jet vanes and to add nitrogen and hydrogen peroxide capacity.
A rocket that knows how to abort
The decisive change was the automatic in-flight abort sensing system. It watched pitch, yaw and roll, chamber pressure and electrical power, and on any anomaly shut the engine down and fired the capsule's escape tower. Deliberately, it could not cut the engine during the first thirty seconds — only the Range Safety Officer could — so that a failing vehicle would not be dropped back onto the pad. The ST-80 inertial guidance set gave way to the simpler LEV-3 autopilot: less precise, but reliable through simplicity.
Six flights, two astronauts
The first attempt, on 21 November 1960, ended with the engine shutting down at the instant of lift-off after an electrical fault. An uncrewed success, the chimpanzee flight carrying Ham and a booster-development shot with a boilerplate capsule followed before the vehicle was judged fit for people. On 5 May 1961 it carried Alan Shepard, the first American in space, and on 21 July Gus Grissom. NASA had bought eight boosters; two never flew, because orbital Atlas missions had made further Redstone flights unnecessary.