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  • Writer's pictureAeryn Avilla

Two to the Moon: Lunar Gemini

Updated: May 16, 2023

During the 1960s, McDonnell Aircraft, the manufacturers of the Mercury and Gemini spacecraft, proposed a wide variety of capsule modifications that would allow the Gemini to perform versatile missions known as Advanced Gemini. These concepts involved everything from docking with a space station to landing on the moon. Due to the number of proposals involving lunar flight, they are grouped into their own category of Advanced Gemini— lunar Gemini.

Lunar Gemini on the moon

The Lunar Gemini of 1962 (Robert Godwin via Smithsonian Magazine)

James Chamberlin, Project Gemini manager, NASA
James Chamberlin (NASA)

The first proposal for using a Gemini capsule to travel to the moon was actually before the Gemini Program, back in the middle of 1961 when it was called Mercury Mark II. Mercury Mark II was what would essentially become Gemini. At this point in time NASA was already committed to a three-man Apollo spacecraft. The bridge between Mercury and Apollo would use a two-man spacecraft based off the Mercury and test rendezvous, docking, and EVA capabilities, all steps necessary to get to the moon. However, McDonnell Aircraft and James Chamberlin, the chief designer of the Gemini spacecraft and the project's first manager, had a better idea— send Gemini on a circumlunar trajectory. He was particularly in favor of any lunar Gemini plans involving Lunar Orbit Rendezvous (LOR), or launching two small spacecraft on one large rocket and having them rendezvous and dock in lunar orbit. He was the first member of the Space Task Group to advocate for this method of landing on the moon, as at the time it had yet to gain the traction it needed. It was not until 1962 that LOR would be chosen as the official landing method. Chamberlin's original 1961 plan would have put people in circumlunar orbit by mid-1965.

When his proposal was rejected, he made another effort at interesting the Space Task Group by including lunar Gemini as part of what he called an "Integrated Apollo Program." It featured the same schedule as his original plan but included more funding for Saturn boosters as well as using Gemini to land on the moon. It would have used a Saturn C-3 to launch a Gemini spacecraft and a lightweight, open cockpit lunar lander designed by NASA Langley. The Saturn C-3 was an early Saturn study that would have used two engines on its first stage and one of the predecessors to the Saturn V. It was in competition with Apollo and was also the first time LOR was legitimately proposed. NASA brass again rejected his proposal but gave McDonnell, Martin, and Lockheed funding for spacecraft and boosters. The actual Gemini program flew more than a year later than originally anticipated but by going off of Chamberlin's revised schedule, the US would have landed men on the moon roughly around the same time it actually did.

NASA Langley's single-person lunar lander design presented to the Space Task Group

NASA Langley's single-person lunar lander design presented to the Space Task Group in 1961

(Robert Godwin via Smithsonian Magazine)

Gemini 11 launch
Gemini 11 launch (NASA)

There were a few different methods of getting Gemini to the moon using different lunar landing techniques. One proposal would have launched two rockets with different payloads into space and have them rendezvous and dock in low Earth orbit (LEO). This method is called Earth Orbit Rendezvous (EOR) and would have eliminated the need for developing the heavy-lift Saturn V. One of its main components was a Transtage, what the Air Force called the upper stage of the Titan III rocket. The Transtage would have launched either on a Titan or Saturn IB. The Gemini would have still launched on the Titan II like it wound up doing during the Gemini Program. Another proposal consisted of a single Titan IIIC launch refueling in LEO before starting its trip to the moon. Yet another consisted of a single launch of a three-stage variant of the Saturn IB. Perhaps the most recognized of these concepts is the Gemini Centaur, which would have seen the Centaur upper stage launch atop a Titan II. Gemini Centaur would have been able to achieve a 72-hour circumlunar flight. Centaur also would have sent crew to the moon for not significantly more than the planned Apollo missions were projected to. However, there were concerns that the Gemini heat shield could not provide the spacecraft enough protection during the higher speed ballistic reentry associated with the trajectory for returning from the moon. NASA proposed a thicker heat shield and more insulation, but these modifications would have made the Gemini too heavy to be launched using a Titan II. Gemini Centaur was very quickly suppressed but other proposals for sending a Gemini to the moon sprang up until even after the Gemini Program itself had ended.

Another proposal of landing on the moon using Gemini was intended to provide a faster and lower-cost alternative to Apollo using lunar direct ascent (LDA), in which one large rocket would launch one large lander.. It would have used a Saturn V to launch a massive single spacecraft consisting of four modules. The Retrograde Module powered by a Rocketdyne RL10 engine would be used for the trans-lunar coast and initial phases of descent. At 5,900 miles (1,800 meters) above the lunar surface the Retrograde Module would be jettisoned and the Terminal Landing Module would perform the final descent. The spacecraft would remain on the moon for about a day before the Service Module performs the lunar ascent firing and TEI. Finally, the Reentry Module, based off the Gemini spacecraft, would return the crew to Earth. This was the last effort by NASA to implement the use of LDA.

1964 brought about the proposal to use a Saturn IB to launch a Gemini to the moon either during the long gap between the end of Gemini and the beginning of Apollo or as a contingency to beat the USSR to the moon if Apollo suffered severe delays. However, those at NASA working on Apollo were not too keen on the idea of Congress receiving a proposal that would undermine support for Apollo. As a result, Headquarters prohibited McDonnell from studying the proposal and restricted all studies involving the use of lunar Gemini to NASA itself.

Titan IIIC rocket launch
Titan IIIC launch (NASA)

The following year astronaut Pete Conrad along with Martin and McDonnell advocated for another circumlunar flight called "Gemini - Large Earth Orbit". It was to use a Titan II-launched Gemini and a Titan IIIC-launched double Transtage to boost the Gemini to translunar speed. The first Transtage would place itself and the other in orbit and rendezvous with the Gemini while the second Transtage would include the Agena docking collar. Even though Conrad was able to spur Congressional interest, NASA Administrator James Webb thought extra funding that would have gone to this project would be better off being spent for Apollo. Conrad was, however, able to get approval for the Agena on his Gemini 11 flight (1966) to boost him to a higher orbit than previously achieved. This flight was the only piece of lunar Gemini that actually took place.

Lunar orbit using Gemini proposals would have seen the Gemini rendezvous with stacked Centaur and Agena upper stages in LEO. The Centaur would place the Gemini and Agena onto a circumlunar trajectory while the Agena would perform trans-lunar insertion and trans-earth insertion. A Titan II rocket would have launched the Gemini and with a Saturn IB launching the upper stages. This means it would have used the EOR method.

NASA's safety review of the Apollo Program following the Apollo 1 disaster in 1967 prompted McDonnell to propose the Universal Lunar Rescue Vehicle, a system with the capability of rescuing an Apollo crew at just about any point during a lunar mission. It included an enlarged capsule with room for five astronauts, two pilots and the three members of the rescued crew. It was considered but ultimately rejected due to lack of funding. However, it spurred the creation of a variety of other Gemini lunar rescue systems.

  1. Gemini Lunar Orbit Rescue Vehicle: This would have been used to retrieve crew stranded in orbit around the moon. Like the original Universal Lunar Rescue Vehicle, it would have consisted of a stretched reentry module to fit the entire stranded crew. It would have launched unmanned on a Saturn V rocket and automatically rendezvous with the stuck Apollo capsule. From there, the crew would perform an EVA to the Gemini and it would boost itself to a trans-Earth trajectory.

  2. Gemini Lunar Surface Rescue Spacecraft: This would have flown a direct mission to the moon using a heavier-lift rocket such as the Titan IIIC or Saturn variant and would have consisted of multiple stages. Its descent stages would have been either the descent stage from the Apollo Lunar Module or Service Module. One configuration used two service modules and one LM decent stage with the LM stage performing the final landing burn as well as ascent from the lunar surface and trans-Earth injection. Another configuration would have used three LM descent stages with the second being used for landing and the third for ascent and TEI. The Gemini could have been reached by astronauts via EVA.

  3. Gemini Lunar Surface Survival Shelter: This derivative would have been sent to the moon ahead of the crewed Apollo mission and landed close to the actual LM landing site. If the ascent stage on the LM failed to ignite, the crew would simply perform one final EVA over to the shelter. However, it was not designed to take off and land again so a Lunar Surface Rescue Spacecraft or different Apollo mission would be sent to get the crew. The Command Module Pilot orbiting overhead would return to Earth alone. The survival shelter consisted of a Gemini reentry module to house the astronauts and a descent stage containing life support systems, consumables, propellant, and descent engine(s).

Cutaway model of the Gemini Lunar Surface Rescue Spacecraft

Cutaway model of the Gemini Lunar Surface Rescue Spacecraft

(McDonnell Douglas)

Lunar Gemini was the most ambitious and longest-lasting portion of Advanced Gemini. It gave the country an alternate to the Apollo Program and helped develop some of the key concepts of flying to the moon. Though it may have been cheaper and faster than Apollo, the development of the Apollo spacecraft paved the way for contemporary spaceflight. Lunar Gemini remains an unfulfilled dream of those who conceived it but provides a unique look into the early days of the Apollo Program and how history may have played out very differently. Do you think any of these proposals was a feasible alternative to Apollo? Let me know in the comments and be sure to like and share this post. Thanks for reading!



  • Portree, David S. F. “Gemini on the Moon (1962).” Wired, Conde Nast, 1 May 2012,

  • Reichhardt, Tony. “Lunar Landers That Never Were.” Air & Space Magazine, 1 Jan. 2008,

  • Wade, Mark. Gemini: Lunar Gemini,

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