Apollo 8 is usually synonymous with Christmas — at least among spaceflight enthusiasts. In 1968, NASA made the daring decision to send Apollo 8 into lunar orbit in the name of getting American men to the moon ahead of the Soviet Union. On Christmas eve, the crew – Frank Borman, Jim Lovell, and Bill Anders – famously read from the book of Genesis. (Left, an artist’s concept of Apollo 8 firing its main engine to return to Earth.)
Sent with only a Command and Service module, the mission is often considered one of NASA’s greatest risks of the space race. But there were other equally audacious lunar missions in the planning stages long before NASA had a viable mission with Apollo 8. As early as 1961, the agency considered sending men to the moon, and even landing them on the surface, with a Gemini spacecraft.
Gemini began its life in 1961 as Mercury Mark II. Built around a larger and more sophisticated Mercury capsule, the program was meant to keep NASA in space and work out the kinks out of a lunar flight profile before actually going to the moon. Apollo was already in the early planning stages at this point as the three-man lunar spacecraft. In October 1962, McDonnell Aircraft, the company who built the Mercury and Gemini spacecraft, published a study of possible lunar missions of a different structure. Most notably, with a Gemini spacecraft. (Above a scale comparison between Mercury, Gemini, and Apollo. Mercury’s influence on Gemini is clear when the two are placed side by side.)
The mission mode outlined in the proposal was direct ascent, the leading contender for a lunar mission mode before lunar orbit rendezvous was selected for Apollo. Direct ascent took the fastest and simplest way to the Moon, launching directly from the Earth to a landing without any rest periods in either Earth or lunar orbit. The mode had the full spacecraft land on the Moon before relaunching towards Earth. While straightforward, direct ascent was an incredibly fuel-intensive method that allowed for almost no redundancies. At each stage, the crew would have limited opportunities to recover form any errors or slipped schedules.
NASA’s then-latest Saturn C-5 launch vehicle, what became known simply as the Saturn V, would launch a two man Gemini crew on their fourteen day direct mission to the Moon. A nominal missions would take 60 hours to reach the Moon and 60 hours to come back; between these transit phases the crew would spend 48 hours on the lunar surface, 24 of which were a built in contingency for the crew to deal with any problems that might arise.
The complete Moon-bound spacecraft was assembled sections. The conical Gemini spacecraft would be the main crew module, analogous to the Apollo Command Module (CM). This was the only habitable part of the spacecraft. Like the then-current design for the Gemini spacecraft, it would support the two-man crew for fourteen days. The CM would also contain the necessary hardware for the crew’s return to Earth — a heat shield for reentry and whatever landing system would bring them safely back to Earth.
Attached to the Gemini CM’s wide end was conical truncated Service Module. The SM would house the bulk of the mission’s environmental control, electrical, communication, and navigation equipment; only in the final phase of the mission would the CM switch to battery power. The SM would also store the bulk of the mission’s propellants — everything the crew would need to launch from the lunar surface and make any course corrections during their return to Earth.
At the SM’s wide end was the Terminal Landing Module. The TLM, analogous to the Apollo Lunar Module’s descent stage, would house everything the crew would need to land on the moon. It would hold enough propellant for the crew to hover above the lunar surface and have sufficient directional control for them to move laterally in search of a suitable landing point.
The TLM would also house the landing gear: four legs, each with three telescopic sections, would give the spacecraft forty0four inches of clearance from surrounding rocks. The legs were filled with an aluminum honeycomb that would absorb the weight of the spacecraft as it settled on the lunar surface. The overall design minimized the weight and length of the landing legs.
The last module of the spacecraft, attached to the TLM on the opposite side from the SM, was a retrograde module. This cylindrical module would hold the propellants for trans-lunar mid course corrections, lunar orbit insertion, and retrograde burn 6,000 feet above the lunar surface; firing the engine would drop the spacecraft towards the lunar surface. It would be jettisoned during descent and the TLM would take over. (The moon, a missed target, as seen from orbit aboard Gemini 7. 1965.)
Separating the lunar landing and launch modules was necessary. Using the same stage for both these phases was a poor choice since any damage incurred during landing could prevent the crew from launching. This was perhaps the more important redundancy built into the proposed mission, one that carried over into the Apollo Lunar Module’s separate descent and ascent modules.
The sectioned design for the spacecraft facilitated a nominal mission. With each phase complete, the spent section would be jettisoned by the crew. As the mission wore on, the spacecraft would get smaller, lighter, and more manoeuverable, making each subsequent portion of the flight easier. Eventually, the crew would left with just the Gemini module to return to Earth.
The Gemini Module
Lunar Gemini I stayed very close to the 1962 “presently configured” fourteen day Earth orbital vehicle. In the event of a launch abort, the astronauts would use the same ejection seats that were in the final Gemini spacecraft. (Left, Gemini in orbit in 1965. Its small windows are visible in this shot.)
Certain modifications were proposed to help the astronauts make a successful lunar landing. Gemini’s two half-moon shaped windows would remain unchanged. Additional mirrors outside the windows would increase the crew’s field of view. During lunar landing, the spacecraft’s hatch would be left open giving the crew a direct view of the surface; the cabin would be depressurized and a clear canopy would cover the opening to stop anything from blowing into the spacecraft. The commander would be in a prone position, looking down at the moon directly. He would also have a bubble canopy. Sticking his head out into this window would give him a full view of his surroundings.
The return to Earth, Lunar Gemini I would use the Rogallo paraglider and the primary landing system. In this sense, it was identical to the then-current Gemini spacecraft.
Lunar Gemini II was similar to Lunar Gemini I. It used the same basic Gemini structure and ejection seats for the astronauts for a launch abort escape system.
The biggest difference was in the Earth-landing system. This variation would use an 84-foot single parachute in lieu of the Rogallo wing and its associated landing gear. It would splash down; only in an emergency would it land on land, but still by parachute. This was a lighter system, freeing up much needed space and weight for the inclusion of more sophisticated systems, particularly a superior navigation system. (Right, the never-flown Rogallo wing landing system.)
When landing on the Moon, Lunar Gemini II would use the same configuration as Lunar Gemini I; windows, mirrors, and the transparent canopy covering the open hatch.
The proposed Lunar Gemini III had some major modifications from variations I and II. This model used an escape tower for abort ejections, like the system used on Mercury and later on Apollo. For the lunar landing, this spacecraft version would replace the transparent canopy with a large, flat window covering the hatch.
This variation would use three 71-foot parachutes to slow the spacecraft to a splashdown or a land landing in an emergency, the same configuration used on the Apollo missions. In an emergency landing, the astronauts would reach the ground by personal parachutes before reentering the spacecraft and using it as a temporary shelter. If they were forced to stay in the spacecraft, shock attenuating couches made the impact of a land landing “tolerable.”
In terms of hardware, Lunar Geminis II and III were most alike — both used hardware that was under development for Apollo in 1962. The sextants, for example, that were used for stellar navigation. The automatic sextant in Gemini I’s SM was replaced by a manual sextant in the Gemini CM on models II and III, the same that was later used on Apollo.
The computer on each spacecraft was the same across the three Lunar Gemini variations. The Gemini computer had been designed for that spacecraft’s hardware. It was much simpler than integrating Apollo computer systems into Gemini configuration.
The Human Factor
While the Lunar Gemini configurations follow the simplest path to the moon, the proposed missions were harder for the crew. The spacecraft’s environmental control wasn’t equipped to provide the astronauts with a shirtsleeves environment — their torsos would have to be vented by climate controlled garments at all times for comfort and safety. The size of the Gemini spacecraft in itself would have posed a challenge to the crew. Barely bigger than the front seat of a small car, it would have been difficult to undertake such complicated manoeuvres as a lunar landing in such a confined space. (Apollo 8′s CM pilot Bill Anders not wearing a space suit on the way to the Moon. 1968.)
As part of the report, McDonnell also considered a direct ascent flight profile with a modified two-man Apollo spacecraft based on the then-current three-man spacecraft. Modifications meant fewer displays and therefore less space and weight dedicated to life support systems; the freed space opened the spacecraft up for the necessary systems and hardware for a lunar landing.
The proposed Apollo configuration used the same segmented structure as the Gemini based mission, supporting a fourteen-day long mission. For the actual lunar landing, live TV feeds of the lunar surface would help the crew make a successful landing. The principle difference reflected the different spacecraft; it would use Apollo rather than Gemini hardware and computers. Minor changes to the CM’s shape would compensate for the lighter spacecraft and ensure an optimal reentry path ending in a pinpoint splashdown. (The Gemini XI spacecraft undergoes maintenance. Workers provide a great scale and show just how small the spacecraft was.)
The idea of sending Gemini to the Moon resurfaced at various times throughout the spacecraft’s lifetime. The idea got as far on Congress, but NASA administrator James Webb killed it. If NASA was going to get any extra money for a lunar program, he said, it ought to go to the spacecraft specially designed to go to the moon, not towards refitting an Earth-orbital vehicle for a lunar flight.
The closest Gemini ever got to the moon was in 1966 when Pete Conrad and Dick Gordon used their Agena target vehicle’s engine to increase their orbit to 850 vertical miles on Gemini XI. Like so many possible uses for Gemini, the lunar mission never went beyond the planning stages. (The Gemini XI mission patch shows the high altitude orbit.)