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In 1961, when President John
F. Kennedy committed the United States to putting a man on the
moon by the end of the decade, America had only 15 minutes of
space experience with the Mercury capsule. In order to work up to
the spacecraft that would be needed to go to the moon, America
developed a new spacecraft, the two manned Gemini. It was named
Gemini after the constellation of the twins, because the Gemini
spacecraft supported two people. It was also the first spacecraft
able to change its orbit and to dock with other satellites, and
gave NASA experience in:
- Longer duration space flight
- Rendezvous and docking,
- Precise control of reentry, landing, ends in space flight
- Extra Vehicular Activity (EVAs), or "Spacewalking"
NASA needed Gemini to provide them with experience in this, because the Mercury capsule was far too simple. And so, on the seventeenth of December 1961, NASA announced their plan to develop a two manned spacecraft capable of safely spending fourteen days in space.
Before January 1962, the Gemini project was referred to as the Mercury mark 2. The craft was almost six meters long, composing of three sections. The sections included the reentry module, retrograde section, and the equipment module. Also, during some flights it was slightly bigger than normal, since it docked with several other satellites (the Agena targets).
Reentry
ModuleThe reentry module was based on the original Mercury capsule, but with many modifications. First, its size was increased to provide 50 percent more room. There were also two hatches, one for each astronaut, and they were designed to be opened and closed in space for the spacewalks. The astronauts sat side by side in ejection seats, and in front of them were two small oval windows with the controls placed in between them. Between the reentry module and the retrograde section was the heat shield.
The retrograde section was a gently tapering cylinder behind the reentry module. It housed eight thrusters for rendezvous and docking, and 4 solid field retro rockets for slowing the spacecraft down before reentry. The Equipment module was an extension of the retrograde section, and carried many of the support systems essential for the flight. It contained most of the electronics, maneuvering thrusters, power (either in the form of batteries, for short missions, or fuel cells, for longer missions), and fuel for the maneuvering thrusters. The equipment modules and did not have a cover, and so foil was placed over it to help control the temperature.
The launch vehicle that was used for the the Gemini program was a modified version of the Air Force Titan 2 ICBM. This liquid fueled, two stage rocket was 3 meters in diameter and 33.2 meters tall. Both stages were fueled by a mixture of unsymmetrical dimethylhydrazine and nitrogen tetroxide, which burns spontaneously on contact, and as a result requires no ignition system. The first stage had two engines while the second stage had only one engine, and steering was accomplished by tilting the engines to one side or another. In order to make the Titan 2 rocket safe, many systems had to either be added or improved. On top of the ejection seats in the Gemini capsule, the Titan 2 rocket added additional instrumentation, a malfunction detection system, and many extra electrical and hydraulic systems.
For the Gemini
project, NASA needed a target for docking and rendezvous
exercises. The target they selected was the Agena D rocket
because it had an excellent performance record for achieving
precise orbits, and it had excellent control and stabilization
abilities. It already had a good record for launching the Ranger
moon probes and the Mariner Venus and Mars probes. This rocket
was 1.5 meters in diameter, 7 meters long, and was developed by
the Air Force for as an upper stage for the Thor and Atlas
rockets. To adapt the Agena rocket for docking with the Gemini
spacecraft, a special collar was fitted to it. This collar
contained a hydraulic system to absorb the shock of connection,
latches to lock it in place, and motors to draw the spacecraft to
a locked position. Once the two ships have been hard docked, the
two spacecraft effectively became one. For example, the electric
connections between Gemini and Agena allowed the astronauts to
send commands to the Agena rocket. They could use Agena's main
engine to shift their orbit, a maneuver which was carried out
several times. Restarting Agena's engine could also be done from
ground control.
Besides docking, another important feature of Gemini was the fact that it could perform extra vehicular activity (EVAs), or spacewalks. Spacewalks were attempted on five separate missions. Half of these were unsuccessful, because the astronauts became overheated. The first spacewalk on Gemini 4, and the third on Gemini 10, the EVAs performed were successful. However, unsuccessful attempts on Gemini 9 and 11 forced NASA to deal with the problem of overheating. A strategy was developed to reduce overheating, by allowing the astronauts to take several frequent breaks inside the spacecraft. The plan worked as Edwin Aldrin proved by making three separate successful spacewalks aboard Gemini 12.
In order to test the Gemini spacecraft before manned missions, both Gemini 1 and 2 were used for unmanned flight tests. Gemini 1 was used to confirm the compatibility of the Titan 2 launch vehicle and the Gemini spacecraft. No attempt was made to separate Gemini and the Titan 2, and both reentered shortly after reaching space. Gemini 2 was also a sub orbital test, where it climbed to 160 kilometers, and tested the reentry system. Both of these tests were successful.
The
first manned mission came on Gemini 3, which was commanded by
Virgil Grissom. Having previously flown on Mercury, Grissom
became the first man to fly into space twice. Copiloted by John
Young, the five hour mission marked the first time a manned
spacecraft shifted orbit. This spectacular mission also marked
the first of a series of successful missions that puts the USA
bed in the space race to the moon.
James McDivitt piloted Gemini 4, which lasted four days. It lasted so long that it was three times longer than the last Mercury mission. This mission set a new endurance record for the Americans, but was broken shortly after by Gemini 5.
Gemini 5 lasted twice as long as Gemini 4, with Gordon Cooper as pilot and Charles Conrad as copilot. This was such a long time for then, it gave the Americans the space flight endurance record for the first time in history. This flight also tested the fuel cells for the first time, which gave them some problems resulting in a shortage of power. At first, the problems threatened to terminate the flight, but they were eventually resolved. Another major task to be done by Gemini 5 was a simulation of the equipment developed for the Agena target vehicle. This was done by releasing a special radar evaluation pod from Gemini, but much of this experiment was canceled to to a shortage of power from the fuel cells.
Gemini
6 was originally planned to attempt a rendezvous with an Agena
rocket, but the Agena failed to reach orbit. Because no other
Agena was available, it was decided that Gemini 6 would wait and
use Gemini 7 as a target. Although the first launch attempt
failed when the main engines of the Titan 2 rocket shut down
seconds after ignition, the second launch attempt was successful
three days later. Once in orbit, Gemini maneuvered to rendezvous
with the already orbiting Gemini 7. Several times during the
flight, Gemini 6 and 7 came within two meters of each other.
Gemini 7 was the longest flight of the Gemini program, and held the space endurance record for the next five years. Frank Borman piloted it, and James Lovell was the copilot. Its objectives included studying the biological effects of long term space flight (the astronauts suffered no ill effects from the long term exposure to weightlessness) and attempting to rendezvous with Gemini 6. For the long flight, special lightweight spacesuit were worn with the understanding that only one crew member could have his spacesuit off at a time. The rendezvous with Gemini 6 went successfully, and for the 20 hours they met, the two crews waved in each other through the windows.
The Gemini 8 spacecraft was the first spacecraft to successfully dock in space. It was piloted by Neil Armstrong, and copiloted by David Scott. After successfully talking with the Agena target for 20 minutes, the two craft began to tumble violently and pilot Neil Armstrong was unable to regain control. An emergency reentry and landing was made after only ten hours in space, but the Agena target remained in orbit.
Gemini 9 was also unsuccessful in its plan to dock with an Agena target. This was because the original Agena target fell back into the Atlantic before ever reaching orbit. Although a quickly assembled replacement did reach orbit, its nose shroud (the covering on the very top of the rocket) was not separated and no docking could take place. Despite this failure, a record breaking two hour EVAs was made.
Gemini 10 and 11 had the first complete successes with docking with the Agena target. Gemini 10, piloted by John young and copiloted by Michael Collins, used the Agena rocket to shift orbit to the Agena left by Gemini 8. Gemini 11, with Charles Conrad as pilot and Richard Gordon copiloting, used the Agena engine instead to gain a record altitude of 1369 kilometers.
Gemini 12, piloted by James Lovell and copiloted by Edwin Aldrin, also successfully docked with the Agena. However, the Agena's main engines failed and no major maneuvers could take place. The mission's major success was that it solved the problem of overheating during EVAs, and three separate EVAs were made by copilot Edwin Aldrin. Gemini 12 was also the last of the Gemini series to be flown.
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