Project Gemini is rightly regarded as the programme that allowed NASA to catch and surpass the Soviet space spectaculars of the early sixties. The highly manoeuvrable 2 person spacecraft allowed astronauts to perform rendezvous, docking and long duration missions as well as providing a platform to test solutions to what became the difficult task of Extra Vehicular Activity (EVA). Gemini systematically proved many of the techniques required for Apollo to succeed in its lunar missions, while dispelling doubts the medical community had about the ability of astronauts to function effectively on longer, more challenging missions.
Coming between Mercury and Apollo, Gemini was a middle step taking NASA beyond short experimental flights and paving the way to meet Kennedy’s goal of a moon landing before the end of the 1960s, but many hoped Gemini could go further. From the earliest planning stages in the late 1950s through to the dawn of the 1970s, a steady stream of Gemini-based concepts crossed the desks of NASA and Air Force managers, but few ever reached the hardware stage. One of the more interesting, and persistent, of these ideas was using Gemini for a circumlunar flight before Apollo would be ready to undertake similar missions. To understand how these ideas came about and why they never came to fruition, we need to look back almost six decades to NASA’s earliest days.
When President Eisenhower decided to create a new civilian agency to oversee America’s space programme via the National Aeronautics and Space Act on July 29th 1958, he gave the new National Aeronautics and Space Administration responsibility for placing an American in space – a role that the Army, Navy and Air Force had all been investigating in the preceding years. On October 7th 1958, NASA formally announced Project Mercury with the aim of sending a one-person capsule aloft atop existing military missiles.
Less than a month after Project Mercury was unveiled, the Space Task Group (STG) was formed at NASA’s Langley Research Center in Virginia. The STG was headed by Bob Gilruth and initially comprised of a mere 45 people. Some, including Max Faget, had already been working on designs for a human satellite for around a year, but it quickly became obvious that the STG now needed to expand rapidly. Fortunately for the nascent NASA, events in Canada were about to deal them a lucky hand. In early 1959 the Canadian government decided to cancel the AVRO Arrow interceptor, meaning many senior aeronautical engineers suddenly found themselves looking for new positions and the STG were only too happy to recruit from this talent pool. One who made the trip south to Langley was Jim Chamberlin, AVRO’s former Chief Designer. He initially took an acting role as head of the STG Engineering and Contract Administration Division as Mercury development began to pick up pace, but it wasn’t long before he began to take a more active role heading up engineering on the Mercury capsule and working closely with the lead capsule contractor, the McDonnell Aircraft Corporation.
Tentative discussions were already underway within NASA about what should follow Mercury. The Goett Committee alongside many supporting panels were convened to help shape future missions as well as the spacecraft and boosters required to perform them. Within these discussions the McDonnell submitted a proposal on September 1st 1959 outlining possible follow-on missions for the programme. These ranged from small orbiting laboratories to unmanned flights with improved heat shields to test reentry from lunar distances, but of particular interest to STG were concepts around lifting reentry, orbital manoeuvres and a 14 day long-duration mission.
By December 1959 the space agency’s proposed direction for the coming decade was outlined by the Office of Program Planning and Evaluation into The Ten Year Plan of the National Aeronautics and Space Administration. A key recommendations was the creation of a new three-person spacecraft capable of both Earth orbital and circumlunar missions in the late 60s, before playing a part in lunar landing plans envisioned for the 1970s. This goal was formalised in July 1960 when Deputy Administrator Hugh Dryden announced NASA’s second crewed spacecraft which would henceforth be known as Apollo.
The decision to undertake deep-space missions sparked further discussions within NASA centres and divergent approaches emerged as to how this could best be achieved. Initially the preferred approach of the STG was to use a huge new booster, NOVA, based on the Saturn development underway at Marshall Spaceflight Center. NOVA would be capable of launching Apollo directly to the moon, but it was clear that any such mission would still require techniques far beyond what could be accomplished in the upcoming Mercury flights. Discussions began to coalesce around rendezvous as a key component of orbital operations for these more complex missions. Key proponents included Langley’s John Houbolt who had been studying rendezvous – initially for space stations, but later as a component of more complex missions – since 1959. In late 1960 NASA HQ saw no immediate need to include the technique as part of Apollo, but as America looked forward to 1961 wondering what changes incoming Democratic President John F. Kennedy would bring, few could have imagined the seismic shifts about to take place for NASA and the STG.
As the new administration found its feet, appointing the politically experienced James Webb as NASA’s new Administrator, hopes were high that Project Mercury would place the first human in space within months, however the Soviet Union would once again beat the United States to the punch. On April 12th 1961 Yuri Gagarin became not only the first human in space, but also the first person to reach orbit. By contrast Alan Shepard’s planned flight was a 15-minute suborbital lob atop a Redstone missile – a feat that Hugh Dryden in his previous role as administrator of the NACA had once described as having about as much merit as a circus human-cannonball stunt when it was proposed by von Braun for the Army’s Project Adam.
Reeling from the Bay of Pigs fiasco, the new President now found himself under pressure to respond to Gagarin’s achievement. Meetings between Kennedy, Webb, Dryden and the chairman of the President’s Science Advisory Committee (PSAC) Jerome Wiesner amongst others, sought to identify an appropriately impressive but technically feasible response. Project Apollo with its promise of trips around the moon and eventual landings became the centre of focus. From the NASA point of view the preliminary work already done on the booster, the spacecraft and even tentative plans for a landing gave sufficient confidence to say that a moon landing within the 1960’s was possible if the full support of Washington was forthcoming. It was agreed that this goal offered the best chance of surpassing the Soviet’s initial superiority and producing an American first.
On May 5th 1961 Alan Shepard roared away from Cape Canaveral placing America firmly back in the space race, albeit someway behind the Soviets. Twenty days later President Kennedy rose to address a joint session of Congress and announced his intention that America should land a man on the moon and return him safely before the end of the decade. NASA’s focus was now squarely on deciding how Apollo would achieve this within the short time available. Decisions would need to be made quickly and new techniques proven to allow a landing to be planned and hardware contracts to be awarded. Fortunately back in Virginia the STG had not been idle.
The Mark II
Even as Mercury reached flight status in 1960, a group within STG had continued to work on plans for a more capable follow-on programme. On February 1st 1961, Gilruth had selected Jim Chamberlin to head up efforts for an expanded Mercury programme and Chamberlin wasted no time in becoming a semi-permanent fixture at McDonnell’s St. Louis plant. Rather than simply make incremental improvements to what he saw as the flawed Mercury design, he began to work with McDonnell engineers on plans for a redesigned version capable of carrying 2 astronauts on a range of complex missions to challenge some of the unknowns on the road to the moon. The resulting design became known as Mercury Mark II and on August 14th 1961 the STG produced the Preliminary Project Development Plan For An Advanced Manned Space Program Utilizing The Mark II Two Man Spacecraft.
The report stated that, where possible, Mark II should use flight proven systems from the Mercury capsule and would be broadly similar in appearance. Major changes would include improved life-support for the 2-person crew and the use of ejector seats rather than a launch escape tower on the basis of simplicity and weight savings. The new spacecraft would be too heavy for Atlas, but an ideal replacement seemed imminent in the Titan II ICBM then under development for the Air Force by the Martin Company. Six key goals were outlined for the new spacecraft, listed in order of perceived priority.
First came Long-Duration Flight with 7-day missions for astronauts and 14-day animal flights. Goal two involved fly a capsule in a highly elliptical orbit to learn more about the Van Allen radiation belts. Initially an uncrewed flight would carry biological samples, but later (if deemed safe) astronauts would undertake the same mission. Third came Controlled Landing with the Mark II’s reaction control system and offset centre-of-gravity giving the pilots an ability to steer the vehicle during reentry. It was also suggested that a paraglider based on research by Francis Rogallo could be used for accurate touchdowns on land. Next on the list came Rendezvous and Docking – key to the concept of future orbital operations – using a modified Lockheed Agena-B placed in orbit by an Atlas as the target vehicle. The fifth goal was a more general requirement for Astronaut Training. It was hoped that these five objectives could be met during a 10-flight programme. If the Mark II performed well during these flights and the goals had indeed been met, an ambitious sixth goal was suggested – circumlunar flight.
Chamberlin’s team and the McDonnell engineers felt that by substituting the more powerful high-energy Centaur stage for the Agena-B, the combined vehicle could boost away from Earth orbit and travel on a free return trajectory to the moon. Once there it could either loop around behind the moon and return immediately or brake into lunar orbit. Although still some way from flight, the Centaur was under development by Convair in conjunction with NASA’s Marshall and Lewis centres and at the time was proposed as an upper-stage for Marshall’s Saturn family of boosters. The Centaur would launch on a second Titan II and once in orbit the Mark II would rendezvous and dock with it before being ‘pushed’ to escape velocity. Modifications proposed for the Mark II included reinforced heat shielding to cope with the higher reentry temperatures, improved radiation protection for the astronauts and additional navigational gear. The report confidently stated that, following build-up flights using the Centaur “It is then proposed that an excursion to the vicinity of the moon be made by mid 1964.”
This sixth objective certainly seemed to have caught the attention of others within NASA. Within a week a revised version of the report was released with one key omission. All overt discussion of circumlunar missions in the Mark II had disappeared with only vague references to “more extensive investigations” that could become a possibility should the Centaur be used as a rendezvous target. Undeterred, by September Chamberlin pushed for an even more ambitious goal proposing a lunar landing involving the Mark II and a small open lander launched using Marshall’s proposed Saturn C-3 booster. The plan is now most notable for its inclusion of Lunar Orbit Rendezvous mode, a concept Chamberlin had been exposed to via Houbolt’s presentations, but on this occasion the idea went no further.
With talk of circumlunar flights quelled for the time being, the frenetic pace of events within NASA showed no signs of abating. On December 7th the Mark II project received official approval and on January 3rd 1962 it also gained a new name – Project Gemini. Chamberlin could now begin setting up his Gemini Project Office (GPO), but they would soon be leaving Virginia behind them. The STG evolved to cope with the challenges to come and headed south to become the Manned Spacecraft Center at NASA’s new facility in Houston, Texas.
The Mode Decision
As the GPO took temporary office space in Houston while construction of a permanent home continued, there was much to do regarding the final specifications and schedules for the new spacecraft, but the moon just wouldn’t go away. Debate raged between the various NASA centres about which mode Apollo should use to reach the moon. While the team at Marshall had championed Earth Orbit Rendezvous to this point, von Braun was pragmatic enough to see the benefits of LOR and gave the mode his, and therefore his centre’s, approval. By July 11th 1962 Webb announced that NASA’s recommended mode for Apollo was LOR, but consensus within NASA didn’t mean the mode decision reached universal approval. Jerome Wiesner was strongly opposed to LOR and PSAC had formed a Space Vehicle Panel in 1961 to examine NASA’s decision making around the mode decision. Wiesner was aided by mathematician and former NASA employee Nicholas Golovin and together they set about challenging what they saw as the dubious merits of LOR with Wiesner at one point describing it as a “technical travesty”. Given his proximity to the President, Wiesner’s opinion could not simply be disregarded by NASA and so, as something of a concession, Webb also stated that new studies into alternative modes were to be conducted prior to any contracts for a lunar lander being awarded.
McDonnell were commissioned to produce a report on a Direct Ascent alternative for the Apollo mission and on October 31st 1962 they published Direct Flight Apollo Study: Gemini Spacecraft Applications, a multi-volume report outlining a Gemini based direct landing using a large augmented capsule to be launched by a Saturn C-5 (later to become the Saturn V). Again the contractor felt they had demonstrated their vehicle’s utility for the lunar mission but again the proposal came to nothing as NASA were able to prevail with their original choice of LOR.
Back in Houston, the GPO and McDonnell had more than enough to keep them busy with development work on Gemini and concerns about teething troubles the Air Force’s Titan II booster. The fate of the Dyna-Soar spaceplane project also hung in the balance in 1963 as Secretary of Defence McNamara sought a comparison between the Titan launched space glider and a military Gemini capsule, to assess which would be more suitable for the Air Force. When Dyna-Soar was eventually cancelled in December of that year, McNamara announced that the Air Force’s man-in-space needs would now be met by a Manned Orbiting Laboratory to be based around a Titan-Gemini combination. Inevitably though, even as NASA’s Gemini readied for it’s initial test flight in early 1964, attention turned back towards the moon.
In April 1964 (coinciding with the launch of Gemini 1), McDonnell presented NASA with a new circumlunar Gemini plan. As the title suggests Gemini Applications for Lunar Reconnaissance proposed a follow-on role for their vehicle beyond the 10 crewed Earth orbital flights NASA planned to fly. Gemini was now being pitched as a solution for obtaining the detailed photographic reconnaissance of the lunar surface needed to identify suitable landing sites for Apollo. The proposal contained a number of vehicle configurations depending on whether the mission would require a simple loop around the moon or insertion into lunar orbit.
In the first option a modified Gemini capsule containing additional photographic survey equipment in the nose would be launched a Saturn 1B with an additional Centaur upper stage. The Centaur would conduct a Trans-Lunar Injection (TLI) burn boosting Gemini and its crew on a free-return trajectory around the moon before being jettisoned. Modifications to the spacecraft would include additional guidance and communications equipment, extra consumables and improved heat shielding and fore-body protection to allow for reentry at higher velocities. The change away from a Titan booster also meant a launch escape tower would be needed rather than the regular Gemini ejection seats. The round trip would take 150 hours, well within the proposed mission duration to be tested by the scheduled Earth orbital Gemini programme.
Recognising that a simple loop around the moon may be of limited utility to the Apollo planners, additional configurations were suggested for a longer lunar orbital mission. In the first of these the Gemini would again launch on a Saturn 1B but this time it would ride atop a modified Agena upper stage. Upon reaching a parking orbit around the Earth, the combined vehicle would then rendezvous and dock with a Centaur launched by a second Saturn 1B. The Centaur would again be used for the TLI burn, this time with the astronauts facing away from the direction of travel. Following a trans-lunar coast the Agena would slow the combined vehicle into lunar orbit where it would conduct its reconnaissance mission for around 24 hours before firing for a second time to boost the Gemini back towards home.
Whereas the first two configurations emphasised the use of existing hardware a third configuration featured an all new combined service and propulsion module. The use of new hardware would doubtless have increased development and testing for this configuration and, although this vehicle would have been considerably lighter, in most respects the mission was identical to the Agena propelled version. As well as the ability to have astronauts conduct a photographic survey of potential landing sites, McDonnell were also keen to stress that their circumlunar Gemini could test Apollo navigation systems and so would provide additional support to that programme.
The timing of McDonnell’s lunar reconnaissance Gemini proposal seems curious. In early 1964 NASA was initiating the Lunar Orbiter programme to provide them with a long-duration robotic mapping capability. Given the reduced cost, complexity and safety concerns around an uncrewed reconnaissance vehicle, it’s hard to see what the USP of the Gemini plan was beyond the possibility of sending Americans around the moon sooner than Apollo (or the Soviets) could manage. An interesting internal memo from John Hammersmith of the Advanced Manned Missions Office to Eldon Hall of Launch Vehicle Programs dated April 3rd 1964 presents Hammersmith’s notes on the relative pros and cons of the various McDonnell configurations. Referring to the plans under the name Gemini L (Gemini Lunar) Hammersmith summarises the likely difficulties surrounding the qualification of vehicle changes (e.g. improved heat shielding), booster availability, upper stage integration, and the availability of launch facilities – some belonging to the Air Force rather than NASA. In many cases he agrees that the various Gemini L plans are a logical follow-on to the scheduled Gemini programme and use proven hardware, but he also points out that they represent no real progression in ability, stating repeatedly for each configuration:
“Other than achieving circumlunar flight prior to Apollo, contributes little to the advancement of spaceflight that is not already programmed.”
He also questions the capability of some of the configurations to accomplish the mission, but perhaps most tellingly sees one of the major drawbacks of the McDonnell plans being the “Possible interference with Apollo”. Whilst Hammersmith’s memo concerns itself solely with the technical feasibility of Gemini L, elsewhere the potential impacts of funding the programme would have been a more pressing cause for concern
The reemergence of Gemini as a circumlunar contender can hardly have been a welcome development for Webb. He had formulated a very deliberate strategy with regards to budget requests for NASA’s human spaceflight activities. Rather than present congress with a best-case financial scenario, he always sought to present the most realistic requests he could however high they were. In doing so he hoped he could avoid having to repeatedly return with additional requests, inviting additional political pressure onto the programme. His approach was certainly appreciated by President Johnson and the push for the moon maintained congressional support during the years of peak spending. However, as a shrewd political operator Webb also knew that if it became widely acknowledged that NASA had in hand other means to get Americans to the moon more quickly and cheaply than Apollo, support could quickly dissolve. There would certainly be no appetite for bankrolling a second crewed lunar programme for circumlunar flight as Apollo development continued.
One Last Joint Push
Given the muted response to McDonnell’s 1964 proposals, it seems even more surprising then that just one year later an entirely new set of circumlunar Gemini plans arrived at NASA, this time from both Martin Marietta – manufacturers of the Titan family of launch vehicles – and McDonnell.
By July 1965 Project Gemini was hitting it’s stride. The first crewed flight, Gemini 3, had demonstrated the basic integrity of the design and tested Gemini’s ability to change it’s orbit – a major first for the US. This was followed by the even more spectacular Gemini 4 in June 1965 with Ed White making America’s first EVA. Gemini 5 was due to fly in August and that would aim for a spaceflight duration record of 8 days in orbit. The major techniques that Gemini had been tasked with demonstrating were being ticked off in a methodical fashion and it must have seemed an ideal time to pitch an ambitious extension to the programme.
In something of a two-pronged attack McDonnell submitted a report titled Gemini – Large Earth Orbit on June 19th 1965. In the report they suggest that with ‘modest revisions’ they feel the Gemini vehicle would be capable of undertaking flights to far greater altitudes via rendezvous with additional propulsion stages. Unsurprisingly one of the very large orbit missions they feel could be undertaken is a circumlunar flight. In essence the proposal is a repackaging of their non lunar-orbital configurations from the previous year, but the major differences centre around the launch vehicles and propulsion stages to be used.
Rather than use NASA’s Saturn 1B, the report proposes two configurations using Titan launch vehicles. The first is for a two-launch mission with the Gemini launching on the standard Titan II before rendezvousing with a modified Titan IIIC transtage launched separately on a Titan IIIC (then in development for the Air Force). The transtage would be fitted with the McDonnell built Target Docking Adapter (TDA) as used in the core Gemini programme. The transtage would then boost the combined vehicle onto a free-return trajectory with the astronauts again facing away from the direction of travel. The second configuration proposed a single launch direct version of the mission with a Titan IIIC launching both the Gemini vehicle and the transtage. In this second configuration, the transtage would be behind the Gemini, so the astronauts would be facing in the direction of travel during the transtage burn.
Martin Marietta followed this with their own study Rendezvous Concept for Circumlunar Flyby in 1967 in July 1965 covering broadly the same ground. What is notable about these 1965 proposals is that they are actually less sophisticated in their aims than the Gemini Lunar Reconnaissance plans submitted by McDonnell the previous year. Without the extra lifting capacity of a Saturn 1B, the best that could be achieved would be a flyby of the moon on a free-return trajectory. Gone is the justification of using the flight to support the upcoming Apollo missions. Instead the sole aim seemed to be a space spectacular ensuring America would beat the Soviet Union around the moon. What the 1965 plans did have in their favour however was support from the Astronaut Office in the shape of Charles ‘Pete’ Conrad.
Conrad, in the midst of training for his August Gemini 5 flight, was enthusiastic about the spacecraft. Like most in the Astronaut Office he saw it as more of a pilot’s vehicle when compared to the simpler Mercury or the larger Apollo. Intrigued by the possibilities of taking the 2-person vehicle beyond the low orbits planned for the Gemini program, he became a willing advocate for the new Martin Marietta/McDonnell plans. It seems his activities were at least partially successful in bringing the concept to a wider audience, but this ultimately became its undoing. Congress grew interested and on August 18th Congressman Olin Teague contacted James Webb on behalf of the NASA Oversight subcommittee of the House Committee of Science and Astronautics asking the Administrator for his opinions on the proposed circumlunar Gemini mission.
Webb responded the following month, using the opportunity to leave no doubt in the mind of Congress as to his opposition to a new lunar programme. Webb not only stated that any new effort would compete for the time and resources vital for Apollo to meet its moon landing deadline, but also referred to his 1961 testimony in support of Kennedy’s original decision in which a lunar landing, not a circumlunar flight, was the stated national objective. He conceded that the Soviets may indeed beat the United States to a circumlunar flight, but that Apollo was the program that would place America in a superior position in the longer term. In effect NASA would only build one piloted lunar-capable spacecraft and that would be Apollo. On October 13th the matter was finally laid to rest in a statement by George Mueller, head of the Office of Manned Spaceflight, in which he said that, while Gemini theoretically could be modified for a circumlunar flight no such mission would take place stating “I see no need for it”. As far as NASA was concerned Gemini would end with the final scheduled orbital flight in 1967 after which all attention would switch to Apollo.
After half a decade of repeated attempts by the major contractors and some within NASA, the dream of Gemini taking the first humans around the moon was finally over.
The Gemini spacecraft that emerged from original discussions of a modified Mercury back in 1959 was undoubtedly a very capable and popular spacecraft. Pilots such as Wally Schirra would state in later years that they regarded their Gemini flights as the pinnacle of their space careers. Having worked so closely with the STG and later the Manned Spaceflight Center, it’s perhaps easy to understand why McDonnell – disappointed not to be building major Apollo hardware – felt justified in seeking an extended Gemini programme just as they had earlier with Mercury. Although circumlunar plans for Gemini ceased after 1965, this was far from the end of the line for McDonnell (or McDonnell Douglas as it became following a 1967 merger with the Douglas Aircraft company). Gemini was still due to fly for the Air Force as part of the Manned Orbiting Laboratory programme and they also used the vehicle as the basis for a resupply ferry first for NASA’s planned Manned Orbiting Research Laboratory (MORL) and later with regards to the larger post-Skylab stations planned for the 1970’s. In fact the Big Gemini proposals of the late sixties were briefly considered a rival to early Shuttle plans.
There’s a lot to admire in the contractor’s persistence, their belief in Gemini and the enthusiasm the vehicle clearly generated in the crews that flew it, but ultimately the decision not to proceed with circumlunar Gemini flights seems to have been a sound one. There never really was a compelling justification for undertaking this mission. However much it may have been touted as a reconnaissance asset for Apollo, a testbed for communications or simply a means of beating the Soviets, NASA’s senior management remained resolute that Apollo was the craft specifically designed for the job and therefore was the only craft that would carry it out. Despite Webb’s protestations otherwise, had the Soviets been on the cusp of making a circumlunar flight things could have swung in Gemini’s direction as few in Congress or NASA would have welcomed coming second to another Soviet space spectacular, but after initial concerns raised by the first Voskhod flight in 1964, it seemed Apollo still stood a good chance of being first around the moon as part of its steady progression of missions towards an ultimate, not a one-off space spectacular.
As it was, both the Soviets and Americans would soon face tragedy as their next-generation spacecraft progressed. The loss of the three AS-204 (Apollo 1) astronauts in a fire on the pad and the death of cosmonaut Komarov at the conclusion of the hastily flown Soyuz 1 mission turned 1967 into a year to regroup, reconsider and reaffirm plans rather than a heated race for the moon. The passing of Sergei Korolev in early 1966 had also dealt the Soviet lunar plans a series blow, although it’s difficult to know how much NASA HQ would have been aware of the chaos and infighting on the other side of the Iron Curtain.
Perhaps the ultimate vindication of Webb’s steadfast opposition to a circumlunar Gemini effort came with the realisation that the Soviet space programme had chosen to pursue separate circumlunar and lunar landing plans, a decision that had stretched resources and funding too far. Indeed the various circumlunar plans from 1963’s 7K-9K-11K plan from Korolev’s OKB-1, through Chelomei’s LK-1 and on to the 7K-L1 ‘Zond’ (when Korolev found himself back in favour following Khruschev’s fall), all bear some resemblance to the various Gemini plans in that they were and end to themselves and very limited in their capabilities.
Of course much of this was only revealed in hindsight, but even as the decision was made in summer 1968 to fly Apollo 8 to lunar orbit in an improvised C Prime mission, the CIA were relatively confident in their assessment that earlier failures in the Zond programme made it highly unlikely that a cosmonaut could reach the moon before 1969. Apollo 8 may have been the first to reach the moon, but it was quickly followed by successive missions leading up to the landing of Apollo 11 in July 1969, meeting Kennedy’s 1961 goal.
One interesting postscript to the story regards Pete Conrad’s support for a circumlunar Gemini mission. Although unsuccessful when lobbying for such a flight in 1965, he did ultimately get to pilot a Gemini/Agena combination to an orbital apogee 850 miles above the earth during his Gemini 11 mission with Dick Gordon. Conrad, who later flew on Apollo 12 and the first Skylab mission later went on to work for McDonnell Douglas, as did former head of the Gemini Project Office, Jim Chamberlin.
In concentrating on the various plans for circumlunar Gemini plans in this post, I decided not to cover Gemini lunar landing plans in anything more than passing details as these are a whole other story in themselves. I recommend David Portree’s Spaceflight History blog for more on these and a multitude of other grand plans that never made it
Project Mercury Capsules: Follow-On Experiments
McDonnell Aircraft Corporation – September 1, 1959
Preliminary Project Development Plan for an Advanced Manned Space Program Utilizing The Mark II Two Man Spacecraft
NASA, Space Task Group – August 14, 1961
Direct Flight Apollo Study,Volume II: Gemini Spacecraft Applications
McDonnell Aircraft Corporation – October 31, 1962
Advanced Gemini, Circumlunar Mission
John Hammersmith Memo – April 3, 1964
Gemini Applications for Lunar Reconnaissance
McDonnell Aircraft Corporation – 10 April 1964
Views on Gemini Circumlunar Flight
James Webb Memo – September 10, 1965
Gemini – Large Earth Orbit Study, Volume 1
McDonnell Aircraft Corporation – 19 June 1965
Rendezvous Concept for Circumlunar Flyby in 1967
Martin Marietta Corporation – July 1965
On The Shoulders Of Titans: A History of Project Gemini
Barton C. Hacker & James M. Grimwood
Chariots For Apollo: A History of Manned Lunar Spacecraft
Courtney G. Brooks, James M. Grimwood & Loyd S. Swenson Jr.
Apollo: The Race To The Moon
Charles Murray & Catherine Bly Cox
Gemini: Steps To The Moon
David J. Shayler
Accessed March 13th 2018
Gemini Lunar Flyby: Always the Bridesmaid
Paul Drye, False Steps
Accessed March 15th 2018
Gemini On The Moon
David S. F. Portree, Wired
Accessed March 13th 2018
Once Around The Moon: The Soviet Circumlunar Race
Chris Petty, The High Frontier
Accessed March 18th 2018