_Gemini 6_’s launch put it 1175 kilometers (730 miles) behind _Gemini 7_ in an orbit which varied from 161 to 272 kilometers (100 to 169 miles) in height. By flying in a lower altitude orbit, _Gemini 6_ astronauts Wally Schirra and Thomas Stafford circled the Earth at a higher velocity, slowing down as they moved to match speed with _Gemini 7_ at the higher orbit. Finally, Schirra jockeyed the _Gemini 6_ spacecraft to within 30 centimeters (1 foot) from _Gemini 7_. They stayed in formation for four revolutions while all four pilots practiced maneuvering. Then _Gemini 6_ broke off and reentered, splashing down on December 16, 1965. _Gemini 7_ went on to complete its 14-day mission which set a record for the longest U.S.-manned space flight which stood until the first Skylab mission. _Gemini 7_ splashed down on December 18. Prime contractor for Gemini was the McDonnell Aircraft Company. _Gemini 7_ is from the National Aeronautics and Space Administration. [Illustration: 84. The Gemini spacecraft.] Rendezvous and Recovery Section Ejection Seat Adapter Equipment Section Reaction Control System Section Cabin Retrograde Section F-1 Engine [Illustration: 85. Thrust chambers of the F-1 rocket engine on the manufacturing line.] Five F-1 engines powered the first stage of the Saturn 5 launch vehicle that launched the manned Apollo spacecraft to the Moon. These engines developed a total thrust of 3.5 million kilograms (7.6 million pounds). They burn liquid oxygen and a form of kerosene at a rate of 13,475 liters (3560 gallons) per second. The propellants are supplied to the thrust chambers by turbopumps driven by gas generators that use a fuel-rich mixture ratio of the same propellants used in the engine. The F-l was developed and produced by Rocketdyne, a division of Rockwell International, under the technical direction of the National Aeronautics and Space Administration, Marshall Space Flight Center, Huntsville. Alabama. The engine on exhibit is from the National Aeronautics and Space Administration. Function Cluster of five providing 3.4 million kg. (7.5 million lb.) of thrust for Saturn 5 first stage Thrust 690,000 kg. (1,522,000 lb.) Propellants Kerosene (fuel) and liquid oxygen (oxidizer) Length 5.8 m. (19 ft.) with nozzle extension Diameter 3.8 m. (12 ft., 4. in.) with nozzle extension [Illustration: 86. The first Apollo/Saturn 5 space vehicle on its way to the launch pad.] Lunar Roving Vehicle [Illustration: 87. The _Apollo 15_ Lunar Roving Vehicle was the first motor vehicle on the Moon.] The Lunar Roving Vehicle (LRV) is a spacecraft designed to carry two astronauts, their life-support systems, scientific equipment, and lunar samples on the airless, low-gravity surface of the Moon.