Mercury-Redstone

The payload to low Earth orbit is zero, and that is not a gap in the record. Mercury-Redstone was never an orbital vehicle. NASA rates it at 1,814 kilograms to an altitude of 189 kilometres on a ballistic path, which is exactly what Project Mercury needed before it trusted anyone to an Atlas. The height of 25.3 metres is the full stack with the Mercury capsule and its escape tower; Marshall’s own project report gives 83.38 feet, and the booster alone is 17.8 metres. Thrust is 78,000 pounds at sea level from a single Rocketdyne A-7, 347 kilonewtons.

What makes this vehicle interesting is everything that was taken out of it. The Jupiter-C it descended from could stage; that capability was deleted. The Jupiter-C burned Hydyne, which is more energetic; Mercury-Redstone reverted to alcohol, which is weaker and less toxic, and kept the elongated tanks so it could burn for twenty seconds longer to compensate. The sophisticated ST-80 autopilot was pulled out and the older LEV-3 inertial system put back. Every one of those is a step backwards in performance and a step forwards in the chance of the passenger surviving.

One footnote worth correcting: NASA’s own Historical Data Book lists the propellant as LOX and RP-1. It was not. Marshall’s project report on the vehicle is explicit that the propellants were ethyl alcohol and liquid oxygen.

Six flew and five succeeded. MR-1 cut off prematurely in November 1960. MR-2 carried the chimpanzee Ham in January 1961 and overshot because the engine ran hot. On 5 May 1961 MR-3 took Alan Shepard 116.5 statute miles up and 303 miles downrange in fifteen minutes, the first American in space, three weeks after Gagarin had already orbited. MR-4 flew Gus Grissom on 21 July 1961 and was a launch vehicle success even though the hatch blew and Liberty Bell 7 sank. Then it was done, in eight months.