All the attention being paid to the Apollo program of 50 years ago is both understandable and justified. It was an amazing technical achievement, all the more amazing because it relied on ground-based computers that occupied rooms rather than desktops—or pockets—and on-board computers that seem laughably simple and underpowered today. But in hailing those achievements and the pioneering solo flights that preceded them, we often overlook the American program that perfected the techniques required to launch three men a quarter of a million miles away from Earth. The Gemini program bridged the gap between the first single-crewed Earth orbital flights of Mercury and the Apollo missions that would send 24 men to the moon and land 12 of them on its surface.
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The Gemini spacecraft was a two-person vehicle. Larger and heavier than the tiny Mercury capsule, it could stay in orbit longer and could actually change its orbital path. Because the planned means of putting men on the moon required perfecting the techniques of rendezvous—two vehicles meeting in space—and docking—physically connecting those vehicles—those needed to be practiced and perfected 150 miles from Earth before trying them in lunar orbit.
There were basically three mission profiles considered for the Apollo moon landing.
- Direct Ascent: A spacecraft would be launched from Earth directly to the moon’s surface and land all three astronauts there. Part of this structure would be left on the moon; and an ascent stage would then return directly to Earth.
- Earth Orbit Renzezvous (EOR): Multiple launches would put parts of a spacecraft into Earth orbit, where they would be assembled for a trip to the moon’s surface as in direct ascent, but from Earth orbit rather than from Earth’s surface.
- Lunar Orbit Rendezvous (LOR): A separate lunar landing craft traveled with a combined command and service module from Earth orbit to lunar orbit. Two men descended to the surface while one remained behind, and the two moon walkers later returned to the “mother ship” in lunar orbit. The landing craft was discarded and the three men returned to Earth after discarding the service module shortly before atmospheric re-entry.
Direct ascent would have required a massive rocket booster even more powerful than the Saturn V to lift all that hardware and send it all the way to the moon. Even so, it was the first option considered. Rendezvous and docking, never even yet attempted in the early 1960s, was considered too difficult and dangerous, especially in lunar orbit where there were no fallback options. But LOR had a champion in John Houbolt, a NASA engineer who relentlessly promoted his plan. It would allow the use of a single Saturn V—not yet built but doable with existing rocket technology—rather than a fleet of them or the development of an even larger booster.
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But rendezvous and docking would have to be something NASA saw as something that could be reliably carried out. They had to be. The safe return of moonwalkers to Earth would depend upon it. The military test pilots who were America’s first astronauts were, of necessity, superb pilots of aircraft. Maneuvering in the atmosphere and maneuvering in orbit have entirely different sets of rules, however. An early attempt by the crew of the Gemini 4 mission to rendezvous with the spent second stage of their booster rocket failed for this reason. The maneuvers are counter-intuitive.
It took Buzz Aldrin (yes, THAT Buzz Aldrin) to help train his fellow astronauts on just how to do this. His doctoral dissertation at M.I.T. was entitled Line-of-Sight Guidance Techniques for Manned Orbital Rendezvous, and he earned the half-mocking, half-admiring nickname from his space-faring colleagues of “Dr. Rendezvous.” He also helped perfect spacewalking techniques based on his experience with scuba diving. His suggestion to train underwater is now part of the training of all astronauts for working in microgravity.
The first rendezvous was actually between two Gemini spacecraft, Geminis 6 and 7.
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The first rendezvous and docking was accomplished by Neil Armstrong (yes, THAT Neil Armstrong) on the Gemini 8 mission. When some thrusters misfired and sent the spacecraft into a dangerous spin, Armstrong and his crewmate Dave Scott were out of contact with ground stations and just seconds away from blacking out. Armstrong’s cool resolution of the situation surely played a part in his selection as the commander of the Apollo 11 mission.
Gemini paved the way for the even more ambitious journeys that were to come with the Apollo program.
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