Titan II GLV

NASA gives the Gemini Launch Vehicle an overall length of 109 feet including the spacecraft, 33.22 metres, made up of 63 feet of first stage, 27 feet of second stage and 19 feet of Gemini. There is no escape tower in that number because there was no escape tower. Stage one produced about 430,000 pounds of thrust at liftoff, 1,912 kilonewtons, and NASA’s Historical Data Book rates the vehicle at 3,200 kilograms to a 185 kilometre orbit.

The reason NASA wanted it was chemistry. Titan II burned a hydrazine blend against nitrogen tetroxide, which are hypergolic: they ignite on contact, so the rocket needed no ignition system at all, and both propellants sit at ordinary temperatures, so there was no cryogenic handling. The lessons from Titan I plus that simplification took the relays, umbilicals, valves and regulators from 172 in the first version to 27.

The same chemistry redesigned the spacecraft. Hypergolic propellants react far less violently with each other than the cryogenics on Atlas, and by June 1961 the argument was whether a Titan II explosion would be mild enough to let a crew use ejection seats instead of an escape tower. Jim Chamberlin had an active distaste for escape towers and got his way. That is why Gemini crews sat on seats, and why this vehicle’s height has no tower in it while Mercury-Atlas and Saturn IB heights do.

The price was POGO. Titan II oscillated along its own length, and steady acceleration already pressed a crewman into his couch at about two and a half gravities. Bouncing at plus or minus another two and a half would have made it hard to read a display or reach a handle. The Air Force could live with that in a missile. NASA set a limit of plus or minus a quarter of a gravity, a tenfold reduction, and the eventual cure was plumbing: standpipes in the oxidiser lines and accumulators in the fuel lines, the same idea as the surge tanks in a hydroelectric plant. The first partial fix came from raising fuel tank pressure, and the official history is candid that nobody was quite sure why it worked.

Twelve launches, twelve successes, from Gemini 1 on 8 April 1964 to Gemini XII on 11 November 1966. Ten of them carried crews. The Gemini 6 pad shutdown, where the engines lit and then stopped with the vehicle still on the pad, was an abort rather than a launch and is not in the count. No American crewed launcher before or since has finished a programme unbeaten.