It’s probably one of the least known space race anniversaries, but this month marks the 50th anniversary of NASA’s selection of lunar orbit rendezvous for the Apollo Program. This one decision shaped the way the whole program looked.

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We’re all used to seeing pictures from the Apollo Program with astronauts standing in front of spidery lunar modules; the small craft took two men to the surface while a third waited in orbit. It’s a mission mode called “lunar orbit rendezvous,” and it was never NASA’s first choice when it considered how to get men to the moon.

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Scientists were thinking about putting men on the moon, and wondering how best to get them there, long before Kennedy’s famous 1961 speech to Congress. After Sputnik’s 1957 launch, it quickly became obvious to engineers at NASA’s (then the National Advisory Committee for Aeronautics) Langley Research Center that politics and not grand visions of exploration would dictate the nation’s future in space.

From that standpoint, the obvious next step in space wasn’t the most logical. The logical step was to get comfortable in Earth orbit before traveling too far, but the obvious step was the moon. NASA could get to the moon with its less powerful rockets, it couldn’t lift the components of a space station.

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The quickest and dirtiest way to get to the moon was with one big rocket. Send it to land on the moon, relaunch, and come home. It would look just like it did on TV. But there were other, less obvious ways like storing a fuel depot in Earth orbit for a spacecraft to refuel on route.

In 1959, Langley engineer William H. Michael proposed such a method with the promise that it would simplify the launch. The proposal did more than just answer the question about to get to the moon, it highlighted the inevitable necessity of knowing how to rendezvous in orbit.

Thomas Dolan, an engineer from Chance-Vought, added another opinion to the lunar mission puzzle. He took the same mission as Michael but added a modular spacecraft that could be discarded with every stage to cut costs even further. Steadily, some mission involving rendezvous was emerging as a favorite.

In 1960, Langley engineer John C. Houbolt, who chaired a special committee for rendezvous study at Langley and gave the Mercury astronauts’ lectures on space navigation, had an epiphany about orbital rendezvous. It was, he realized, the only way to send a large spacecraft to the moon. It would cut launch costs in half and could be done faster since it didn’t require development of huge rockets. He was so convinced of this that resolved to work hard convincing NASA higher ups that rendezvous was an inevitable part of the agency’s future endeavors.

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Houbolt lauded rendezvous to anyone who would listen, but met resistance along the way. On Dec. 14, 1960, he presented the method in Washington D.C. and Max Faget, the man behind the Mercury capsule, called shenanigans. He didn’t believe Houbolt’s claim that rendezvous could cut launch costs by 50 percent. The only way to get to the moon, said Faget, was with a giant rocket — a method called direct ascent. Wernher von Braun agreed. He was developing the massive eight-engine Nova rocket for the job.

Then on May 25, 1961, Kennedy famously promised his country the moon and NASA needed to pick a way to get there. Without a mode, there was no point in developing the spacecraft.

Initially, direct ascent emerged on top. But when engineers started crunching the numbers it emerged as an impossible method. The proposed Nova rocket would need too much fuel, be too heavy, expensive, and take too long to build to reach the moon in Kennedy’s time frame.

The new favorite-by-default was a method called Earth orbit rendezvous, or EOR. EOR had two smaller rockets launch the components of a lunar spacecraft separately before they docked in Earth orbit. It was an appealing method because of what it promised to teach NASA: building a spacecraft and sending it to the moon would be excellent practice for building a space station and launching mission to other planets. Space station proponents like von Braun lobbied hard for EOR, but again the cost and time frame came with a penalty NASA couldn’t afford.

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The only option that remained, the one that had promised to cut launch costs from the start, was lunar orbit rendezvous.

Still, it took over a year for all the men behind every piece of Apollo to unanimously support the decision. Not until June 7, 1962, did von Braun admit that LOR would get men on the moon by the end of the decade. A little more than three weeks later on June 25, the Manned Spaceflight Management Council unanimously agreed that LOR was the only way forward with Apollo.

By the time this decision was made, one of the precious nine years NASA had to land men on the moon was gone. The other outcome of that June 25 meeting was the recommendation that construction of the lunar module begin immediately.

Image: 22 April 1972: The Apollo 16 Lunar Module (LM) “Orion” in early lunar liftoff phase is featured in this lunar scene at the Descartes landing site. The still picture is a reproduction taken from a color television transmission made by a TV camera mounted on the Lunar Roving Vehicle (LRV).