How NASA's Gemini Spacecraft Worked (Infographic)

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.