Today is the 47th anniversary of the, which, as you may know, turned out pretty damn well. But that outcome was by no means assured. What if there was some huge design flaw in the myriad of systems in an Apollo or Saturn V rocket? Would we have been boned? Of course not. There’s always a backup plan.

In the case of the America’s ambition to land on the moon, the backup plan was a little bit bonkers because it relied on a cramped, two-person spacecraft never really intended for use in lunar orbit. It was a plan (well, really, a series of plans) that would have made a lunar landing possible with less of everything—astronauts, fuel, mass, interior volume, launch thrust, and, in one particularly exciting variant, the entire outer body of a lunar lander.

These backup plans all had one thing in common: they were based around the Gemini spacecraft.

The Gemini (originally known, poetically, as the ‘Mark II Two Man Spacecraft”) was America’s second crewed spacecraft design, after the relatively crude one-person Mercury capsules.

The Gemini capsules were sort of the hot rods of early spacecraft: a little two-seater, with the option to be a convertible, if you flew it with the doors open. Which we did on Gemini 4, when Ed White became the first American () to walk in space.

The Gemini missions achieved a lot of firsts: first rendezvous and docking, a in-space duration record (the two-week ), highest Earth orbit by a manned spacecraft (850 miles, ), and the in space (Gemini 3).

Gemini was a remarkably capable and flexible platform, but it was still quite limited. Unlike the Apollo capsules used to actually go to the moon, in a Gemini there was no room to get up out of your seat and move around. The cabin was described as being “,” which is probably not ideal for a long lunar mission.

Still, that didn’t stop anyone from trying.

As early as 1961, before Gemini even had an official name, NASA was . There are a number of reasons why this happened.

First, nobody was really sure what the Soviets were doing, what they were capable of, and everyone assumed they were on track to getting to the moon, possibly before we did, which was the last thing anyone in the US government wanted to happen.

Even if the Soviets only managed to orbit around the moon before an American crew did, that alone would be considered a disaster, so plans were made for a possible Gemini-based circumlunar mission that would be independent of crucial Apollo hardware.

A lunar-orbiting Gemini would be prepped for a long-duration mission and modified with a heat shield designed to withstand the faster re-entry from lunar orbit. You can see a full breakdown of the weights of the modified “Gemini L” here:

So, they were looking at a mass of about 9,000 lbs for the Lunar-orbiting Gemini. As a comparison, the CSM, the spacecraft configuration that eventually did orbit the moon in 1968, weighed 63,650 lbs.

These initial studies suggested that a moon-orbiting Gemini could happen as early as 1964, and they proposed a number of launch variations, including ones that used the Saturn 1B (much smaller than the Saturn V moon rocket) and some that used no Saturn hardware at all, relying on the Air Force’s Titan III rockets.

So, even if both the Apollo and Saturn projects had turned out to be total failures, it looks like we could still have orbited the moon, albeit much less comfortably.

But what about actually landing on the moon? The Gemini-lovers had plans for that, too. And their plans included getting one astronaut on the, and much more cheaply (some estimates give the original Gemini-to-moon plans as the cost of Apollo). And probably more frighteningly.

NASA’s designed the 1961 Gemini lunar landing plan, and its total launch mass would have been 1/5 that of Apollo’s. Chamberlin’s plan included launching the Gemini on a rocket (proposed, never built) which was significantly smaller than the Apollo’s Saturn V.

The lunar lander itself would be launched separately on a Titan II, and would have been a completely open-cockpit, stripped-down rocket engine on legs. This lunar lander design was known as the , and would have been about a third of the weight of the Lunar Lander used by Apollo.

With the limited space and the open-cockpit, bare-bones lunar lander, perhaps the US could have landed an astronaut on the moon by 1966, but those missions would have been much more limited than what was possible with the Apollo systems.

Maybe if absolutely everything went wrong with the Apollo program and the Saturn V rocket, the Gemini approach would have made some sort of sense, but as it was going with Apollo was the right decision for NASA to make, even if it did take three years longer and cost a massive payload’s worth of more money.

There were still a lot of people who really, really must have wanted to get a Gemini on the moon, though, because even after it was clear that Apollo was going to be the program to go to the moon, another lunar-landing Gemini was proposed.

This was the Gemini Lunar Surface Rescue Spacecraft (LSRS), and it was essentially a Gemini capsule turned into a remotely operated lunar lander. The thinking was that if something went wrong with either the Lunar Lander or even the orbiting Apollo CSM, a Gemini LSRS could be remotely landed on the moon near the Apollo Lunar Module, the two astronauts could moonwalk over to the rescue Gemini, climb in, and head directly back to earth, with no need to dock and transfer to an Apollo CSM.

This configuration of Gemini was even featured in a 1967 movie, Countdown:

It was a pretty cool idea, all told, and all of these programs were a testimony to the flexibility of the Gemini hardware and the fevered, fertile imaginations of the engineers that designed them.

Still, the Gemini program was basically done by that point, and none of these later developments really made all that much sense, in the big picture.

Even early on, when the Soviet paranoia was at its peak, it wouldn’t even have been necessary, since the Soviet lunar program was by their painfully over-complicated launch vehicle.

Even so, I still like to imagine what a quick-and-dirty Gemini lunar mission may have been like, and it gives me a strange sense of scrappy pride to know the extent of the determination to get to the moon that we had, even if it meant strapping some guy into a rocket-powered lawn chair and pointing him at the moon.