How NASA's Gemini Spacecraft Worked (Infographic)
Paving the way for Apollo's missions to the moon, the Gemini program provided much-needed experience for astronauts in space.
Credit: By Karl Tate, Infographics Artist
To follow the successful series of Mercury flights, NASA planned the Gemini spacecraft for the mid-1960s. Gemini’s goals were to test astronauts on long-duration Earth orbit flights; to practice orbital rendezvous and docking, which was a requirement for moon landing missions; and to practice re-entry and landing. 
Of the 18.5-foot (5.61 meters) Gemini spacecraft, only the conical re-entry module would return to Earth. The 90-cubic-foot (2.55 cubic meters) pressure vessel would be home for two astronauts for up to 14 days.
Like Mercury, the Gemini capsule would be launched atop a missile designed to lob nuclear bombs across the planet. The military Titan II missile became operational in 1963, and was capable of carrying one Mk/B53 nuclear warhead of 9 megatons of explosive power.
The modified Titan II launched 12 Gemini spacecraft between 1964 and 1967.
Gemini astronauts were alotted 2,500 calories per day. Most of the food was dehydrated, with 99 percent of the water removed to save weight. Gemini 3 was the first mission where astronauts were given solid food.  On Mercury flights, puréed food was supplied in foil tubes. To prepare the Gemini food, astronauts would inject cold water into the packets. Hot meals would not be available until the Apollo missions.
To prepare for Apollo flights to the moon, astronauts practiced matching orbit and speed with another spacecraft, a process called rendezvous. An unmanned rocket, the Agena, was launched as a target for several Gemini flights. Gemini 8, piloted by Neil Armstrong and Dave Scott, nearly ended in disaster when a malfunction during docking caused their Gemini to spin out of control.
When the Gemini 6 mission was called off due to failure of the Agena target vehicle, a joint mission with Gemini 7 was held instead. Frank Borman and Jim Lovell, conducting a 14-day endurance mission aboard Gemini 7, were briefly visited by Walter Schirra and Thomas Stafford in Gemini 6.
Five astronauts conducted a total of nine spacewalks during the Gemini program. The first was Ed White’s 20-minute walk on Gemini 4, coming three months after Alexei Leonov’s historic first-ever spacewalk in March 1965.
Buzz Aldrin held the record for most spacewalks on a Gemini flight, with a total of three spacewalks  spread over 5.5 hours on Gemini 12.
To aid with spacewalking, Ed White carried a compressed-gas gun. This provided only 20 seconds or so of thrust. An elaborate jetpack, called the Maneuvering Unit, was carried on Gemini 9 but not tried because astronaut Gene Cernan’s overexertion caused him to terminate the spacewalk early. Similar jetpacks were finally tested in space in the 1980s.
Although NASA only meant for the Gemini spacecraft to be used until the bigger and more capable Apollo was ready to fly, aerospace manufacturer McDonnell saw a brighter future for Gemini.
Proposed missions included Geminis adapted to work with the Air Force’s MOLAB manned surveillance station. Military Geminis were nicknamed “Blue Gemini.” MOLAB and Blue Gemini never flew.
As a backup or supplement to Apollo moon missions, a Gemini beefed up to handle lunar orbit flights was designed. Unfortunately for McDonnell, NASA chose instead to focus all its efforts on readying the Apollo spacecraft for moon-landing missions.

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