9. Gemini revealed a two-part spacecraft with only the capsule returning to earth
The Gemini orbiting vehicle was a two-part spacecraft which consisted of an adapter module and a re-entry module. The re-entry module was the capsule, considerably larger than Mercury, and in an improvement over Mercury used all solid-state electronics, modularized for ease of replacement. The booster system consisted of rocket engines which used fuel that spontaneously combusted when combined with an oxidizer, providing a more stable lift vehicle, and a less dangerous one for the astronauts. Because the risk of rocket explosion was lower and the size of such an explosion was smaller, Gemini was equipped with ejection seats, rather than an aborted rocket to pull the capsule away from the booster.
To the general public, Gemini’s ten missions were a rousing success, including America’s first spacewalk and television transmissions from space, but underneath the glamor presented by NASA there were problems, several of which could have resulted in fatal accidents had the crews and ground support not have come up with innovative ways of dealing with them. Gemini had only two test flights of unmanned spacecraft before beginning manned flights in 1965, using the Titan II rocket for the booster on all of them. The Titan II was the primary rocket used by the US Air Force for its ICBM program at the time, and it took considerable testing and modification before it was approved for use in manned flights.