Declaring success after Gordo Cooper's 20 orbit flight, and trying to keep up with the Soviet program, Project Mercury was brought to an abrupt end and Project Gemini was started.

While the Mercury capsules held one astronaut in a shoebox, the Gemini capsules held two. The Gemini Program -- begun only three years after the first human space flight had extremely ambitious goals.

Project Gemini's objectives were:

To subject two crewmembers and supporting equipment to long-duration flights, a requirement for projected later trips to the Moon or deeper space.

To effect rendezvous and docking with other orbiting vehicles, and to maneuver the docked vehicles in space, using the propulsion system of the target vehicle for such maneuvers.

To perfect methods of reentry and landing the spacecraft at a pre-selected land-landing point (ie, neither Russia nor China).

To gain additional information concerning the effects of weightlessness on crew members and to record the physiological reactions of crew members during long-duration flights.

To accomplish Extra Vehicular Activities (EVA) or space-walks outside the protection of the space craft.

The astronauts, now numbering 16, would have to train quickly and accomplish all of these tasks as all of them were required for a successful landing on the moon within, now 6 years.

Gemini was originally seen as a simple extrapolation of the Mercury program, and thus early on was called Mercury Mark II.

The actual program had little in common with Mercury and was in fact superior to even Apollo in some ways.

This was mainly a result of its late start date, which allowed it to benefit from much that had been learned during the early stages of the Apollo project (which, despite its later launch dates, was actually begun before Gemini!).

Its primary difference from Mercury was that the earlier spacecraft had all systems other than the reentry rockets situated within the capsule, to which access of nearly all was through the astronaut's hatchway, while Gemini had many power, propulsion, and life support systems in a detachable module like a huge bowl.

Many components in the capsule itself were reachable each through its own small access door.

The original intention was for Gemini to land on solid ground instead of at sea, using a paraglider rather than a parachute, and for the crew to be seated upright controlling the forward motion of the craft before its landing. To facilitate this, the parachute cord did not attach just to the nose of the craft; there was an additional attachment point for balance near the heat shield. This cord was covered by a strip of metal between the doors.

Early short-duration missions had their electrical power supplied by batteries; later endurance missions had the first fuel cells in manned spacecraft.

The "Gemini" designation comes from the fact that each spacecraft held two people, as "gemini" in Latin means "twins". Gemini is also the name of the third constellation of the Zodiac and its twin stars, Castor and Pollux.

Unlike Mercury, which could only change its orientation in space, the Gemini spacecraft could alter its orbit.

An unmanned Agena module was designed and launched for each Gemini flight to learn and test skills that would be needed to go to the moon. It was used for docking, tethering, EVAs and even used as a rocket to pull the Gemini spacecraft to high altitudes.
The unsung Agena is the header image in the Gemini sectiion of this site.

Gemini astronauts and vehicles were meant to dock with the Agena Target Vehicle (above), which had its own large rocket engine and was used to perform large orbital changes.

Gemini was the first American manned spacecraft to include an onboard computer, the Gemini Guidance Computer, to facilitate management and control of mission maneuvers.

It was also unlike other NASA craft in that it used ejection seats, in-flight radar and an artificial horizon - devices borrowed from the aviation industry. Using ejection seats to push astronauts to safety was first employed by the Soviet Union in the Vostok craft manned by cosmonaut Yuri Gagarin.

Gemini was designed by a Canadian, Jim Chamberlin, formerly the chief aerodynamicist on the Avro Arrow fighter interceptor program with Avro Canada. Chamberlin joined NASA along with 25 senior Avro engineers after cancellation of the Arrow program, and became head of the U.S. Space Task Group’s engineering division in charge of Gemini.

So Gemini was the first internationally built set of spacecrafts.

The main contractor was McDonnell, which had lost out on main contracts for the Apollo Project. McDonnell sought to extend the program by proposing a Gemini craft which could be used to fly a lunar orbitor mission and even achieve a manned lunar landing earlier and at less cost than Apollo, but these proposals were rejected.


Deke Slayton, who had been made inactive as an astronaut because of a heart murmur was made head of the Astronaut Office had the main role in the choice of crews for the Gemini (and Apollo) programs.

This selection process, with the prospect of more ambitious missions that would follow with Apollo, became even more political than in the Mercury Program.

With Gemini it became a procedure that each flight had a primary crew and backup crew and that the backup crew would rotate to primary crew status three flights later.

Slayton also intended for first choice of mission commands to be given to the four remaining active astronauts of the Mercury Seven, Alan Shepard, Gus Grissom, Gordon Cooper and Wally Schirra.

John Glenn had retired from NASA in January 1964 shortly after President Kennedy was assassinated, and was elected as a Senator from Ohio - a position he held for more than 20 years.

In late 1963, Slayton selected Alan Shepard and Thomas Stafford for Gemini 3, James McDivitt and Ed White for Gemini 4, and Wally Schirra and John Young for Gemini 5 (the first Agena rendezvous mission).

Gemini 3 was backed up by Gus Grissom and Frank Borman, who were also slated for Gemini 6, the first long-duration mission.

Finally Pete Conrad and James Lovell were assigned as the backup for Gemini 4.

Delays in the production of the Agena Target Vehicle caused the first rearrangement of the crew rotation.

The Schirra and Young mission was bumped to Gemini 6 and they now were the backup crew for Shepard and Stafford.

Grissom and Borman now had their long-duration mission assigned to Gemini 5.

The second rearrangement occurred when Alan Shepard developed Meniere's disease, an inner ear problem.

Gus Grissom was moved to command Gemini 3.

Slayton felt that Young was a better personality match with Grissom and switched Stafford and Young.

Slayton tapped Gordon Cooper to command the long-duration Gemini 5. Again for reasons of compatibility he moved Pete Conrad from being the backup commander of Gemini 4 to be the pilot of Gemini 5, and Frank Borman to the backup command of Gemini 4.

Finally he assigned Neil Armstrong and Elliot See to be the backup crew for Gemini 5.

The third rearrangement of crew assignment occurred when Deke Slayton felt that Elliot See wasn't up to the physical demands of EVA on Gemini 8.

He reassigned Elliot See to be the prime commander of Gemini 9 and put Dave Scott as pilot of Gemini 8 and Charles Bassett as the pilot of Gemini 9.

The fourth and final rearrangement of the Gemini crew assignment occurred after the deaths of Elliot See and Charles Bassett in a plane crash in St. Louis.

The backup crew of Tom Stafford and Eugene Cernan was moved up to become the new prime crew of Gemini 9.

James Lovell and Edwin "Buzz" Aldrin were moved from being the backup crew of Gemini 10 to be the backup crew of Gemini 9.

This cleared the way through the crew rotation for Lovell and Aldrin to become the prime crew of Gemini 12. This rearrangement is what finally determined the makeup of the early Apollo crews and these events were decisive in determining who would be in position to first walk on the Moon.

In his autobiography Deke! Slayton relates that he would probably have replaced Aldrin with Eugene Cernan, the backup pilot for Gemini 12, if the second flight of the AMU had flown on Gemini 12.

The United States Air Force also had an interest in the system, and decided to use its own modification of the spacecraft as the crew vehicle for the Manned Orbital Laboratory - the first (planned) Space Station. To this end, one of the unmanned Gemini spacecraft was refurbished and flown again atop a mockup of the MOL, sent into space by a Titan III-M. This was the first time a spacecraft went into space twice.

The USAF also had the notion of adapting the Gemini spacecraft for military applications, such as crude observation of the ground (no specialized reconnaissance camera could be carried) and practicing making rendezvous with suspicious satellites. This project was called Blue Gemini.

The US Air Force did not like the fact that Gemini would have to be recovered by the US Navy, so they intended for Blue Gemini eventually to use the paraglider and land on three skids, something from the original design of Gemini.

At first some within NASA welcomed sharing of the cost with the USAF, but it was later agreed that NASA was better off operating Project Gemini by itself. The "Manned Orbital Laboratory" program was cancelled in 1968 and Blue Gemini too was cancelled without any use by military astronauts.