The Gemini program is the middle child of human spaceflight; Mercury is the first and therefore well remembered and Apollo is the over-achieving younger sibling who gains fame and fortune. In the mix Gemini is often forgotten. David Harland's book helps to rescue the program from its obscurity. While it was initially conceived before Apollo got underway in 1961, after the commitment to the Moon landing Gemini morphed into a program to develop the skills necessary to reach the Moon. NASA closed most of the gap by experimenting and training on the ground, but some issues required experience in space. Three major areas immediately arose where this was the case. The first was the ability in space to locate, maneuver toward, and rendezvous and dock with another spacecraft. The second was closely related, the ability of astronauts to work outside a spacecraft. The third involved the collection of more sophisticated physiological data about the human response to extended spaceflight.
To gain experience in these areas before Apollo could be readied for flight, NASA devised Project Gemini. Hatched in the fall of 1961 by engineers at Robert Gilruth's Space Task Group in cooperation with McDonnell Aircraft Corp. technicians, builders of the Mercury spacecraft, Gemini started as a larger Mercury Mark II capsule but soon became a totally different proposition. It could accommodate two astronauts for extended flights of more than two weeks. It pioneered the use of fuel cells instead of batteries to power the ship, and incorporated a series of modifications to hardware. Its designers also toyed with the possibility of using a paraglider being developed at Langley Research Center for "dry" landings instead of a "splashdown" in water and recovery by the Navy. The whole system was to be powered by the newly developed Titan II launch vehicle, another modified ballistic missile developed for the Air Force. A central reason for this program was to perfect techniques for rendezvous and docking, so NASA appropriated from the military some Agena rocket upper stages and fitted them with docking adapters.
Problems with the Gemini program abounded from the start. The Titan II had longitudinal oscillations, called the pogo effect because it resembled the behavior of a child on a pogo stick. Overcoming this problem required engineering imagination and long hours of overtime to stabilize fuel flow and maintain vehicle control. The fuel cells leaked and had to be redesigned, and the Agena reconfiguration also suffered costly delays. NASA engineers never did get the paraglider to work properly, and eventually they dropped it from the program in favor of a parachute system like the one used for Mercury. All these difficulties shot an estimated $350 million program to over $1 billion. The overruns were successfully justified by the space agency, however, as necessities to meet the Apollo landing commitment.
By the end of 1963 most of the difficulties with Gemini had been resolved and the program was ready for flight. Following two unoccupied orbital test flights, the first operational mission took place on March 23, 1965. Mercury astronaut Gus Grissom commanded the mission, with John W. Young, a naval aviator chosen as an astronaut in 1962, accompanying him. The next mission, flown in June 1965, stayed aloft for four days, and astronaut Edward H. White II performed the first American extravehicular activity (EVA), or spacewalk. Eight more missions followed through November 1966. Despite problems great and small encountered on virtually all of them, the program achieved its goals. Additionally, as a technological learning program, Gemini had been a success, with 52 different experiments performed on the 10 missions. The bank of data acquired from Gemini helped bridge the gap between Mercury and what would be required to complete Apollo within the time constraints directed by the president.
This story is well-told in Harland's account. It is not an official history of the program, but concentrates on the story of the planning for and the execution of the 10 human Gemini missions. For the official history see "On the Shoulders of Titans: A History of Project Gemini" (NASA SP-4203, 1977), by Barton C. Hacker and James M. Grimwood. This is available on-line at [...]