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Gemini: Lunar Gemini

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Gemini Lunar SRS Exploded view of the Gemini Lunar Surface Rescue Spacecraft. From top to bottom: the Gemini re-entry module; the lunar ascent stage; the lunar descent stage; the lunar orbit insertion stage. Credit: McDonnell Douglas

Right up to the end of the Gemini program, the Gemini spacecraft was considered by its contractor and certain factions within NASA as an alternate means of reaching the moon. The Gemini re-entry capsule, smaller and lighter than that of Apollo, would allow direct launch of a mission to the moon using a single rocket. Alternatively, rendezvous and docking of components launched by two small rockets (Titan 3C's or Saturn IB's) would eliminate the need for development of the Saturn V.

There were several proposals for lunar Gemini, right up to the very end of the program:

• Circumlunar flights by Gemini, boosted by Centaur, as part of the original Mercury program plan (August 1961)

• Lunar landing by Gemini, boosted by a Saturn C-3, in competition with Apollo, as part of the revised original Gemini program plan (September 1961)

• Use of Gemini, launched atop a Saturn V, as a Lunar Logistics and Rescue Vehicle (September 1962)

• Circumlunar Gemini, launched by Saturn IB, to replace cancelled Apollo circumlunar flights (March 1964)

• In the wake of the Apollo fire, use of Gemini B, launched atop a Saturn V, as a Universal Lunar Rescue Vehicle (April 1967)

At its birth Gemini was known as the Mercury Mark II program. NASA was already committed to the three-man Apollo spacecraft and considered Gemini an interim spacecraft to test rendezvous, docking, and EVA techniques before Apollo was available. But NASA's James Chamberlin and McDonnell Aircraft considered Gemini as a viable competitor to Apollo for the circumlunar and lunar landing missions. Such proposals might be welcomed by the current 'cheaper, better, faster' NASA. But in 1961, as a direct challenge to the Apollo project and Lyndon Johnson's dream of a Southern High Technology Crescent, they were anathema.

The original August 14, 1961 Mercury Mark II program plan went like this:

The Centaur would be launched atop a Titan II booster. The lunar Gemini spacecraft would have weighed 3,170 kg, an extra 270 kg over the basic rendezvous Gemini. The difference consisted of a backup inertial navigator and additional heat shielding for re-entry at 11 km/sec instead of 8 km/sec. This program was estimated to put an American around the moon for only $ 60 million more than the basic $ 356 million program. An even more aggressive alternative, a nine-flight program, was promised to cost only $ 8.5 million more than the basic program and fly around the moon in May 1964! This first attempt to fly Gemini to the moon was quickly suppressed, and a revision of the plan was issued only a week later, with all mention of lunar flights deleted.

September 1961 - Gemini Lunar Landing

But the idea seemed too good to just drop and a month later Chamberlin came up with an even more ambitious plan. He proposed to not just fly around the moon, but to land on it, at a cost 1/20 of that of the Apollo project. The key was the use of the technique of lunar orbit rendezvous and a bare-bones, open cockpit lunar module. This would weigh 4,372 kg in the storable propellant version or 3,284 kg in the cryogenic Lox/LH2 version (calculated propellant loads 3,500 kg and 2,200 kg, respectively). The total mass to be injected into an escape trajectory toward the moon would be no more than 13,000 kg, one fifth of the 68,000 kg planned for the Nova-boosted direct-lunar landing approach favored at that time. At this mass, instead of Nova, a Saturn C-3 launch vehicle could be used. The flight schedule would have been delayed by a year in order to develop a more capable spacecraft. However by launching every 45 days instead of every 60 days Gemini would still put an American on the moon by January 1966:

The lunar module would have been launched separately by Titan II for the three Earth orbital docking missions. This moon landing project was projected to cost $ 584 million 'plus the cost of two Saturn C-3's'.

Chamberlin was actually the first member of the Space Task Group (STG) to advocate lunar orbit rendezvous (LOR) as a method for reaching the moon. Earlier efforts through 1960 and 1961 by Robert Houbolt and other engineers at Langley to interest STG in the method had been seen as the impractical musings of theorists. Chamberlin and McDonnell Aircraft did not fall in this category. They saw clearly that separating the re-entry and lunar landing functions allowed optimized spacecraft designs for each role, and solved many of the intractable engineering problems the direct-ascent advocates were struggling with.

Chamberlin made one last effort at the end of September to interest STG in including lunar Gemini as part of an "Integrated Apollo Program". This involved the same flight schedule as advocated earlier, but with the cost estimate now firmed up at $ 706 million (including the Saturn boosters!), and the lunar module mass cut to 1,800 kg. NASA brass still rejected the lunar aspects of the plan, but told STG to go ahead with negotiations with McDonnell, Martin, and Lockheed for the spacecraft and boosters. Chamberlin submitted the revised plan without lunar flights on October 27, and this was approved as the basis for project Gemini.

The actual Gemini project as flown was over a year late to the original optimistic plan. This was due to delays in development of both the Titan 2 launch vehicle and the Gemini paraglider landing system. The pivotal 14-day flight actually came in December 1965 versus January 1964 in the first Mercury Mark II proposal and August 1964 in the September 1961 plan.

It is possible to estimate when Chamberlin's Gemini moon landing would have actually occurred based on the actual delays to Gemini. It must be considered that the time necessary to develop the Saturn C-3 could not have been much less than that actually taken for the C-5 (the final December 1961 C-3B configuration differed from the C-5 only in the propellant loading in each stage and in having three F-1 engines in the first stage as opposed to five in the C-5). Therefore, with perfect hindsight, if Gemini had been selected in lieu of Apollo, the actual final program would have looked about like this:

So in the end, the first lunar landing would have been moved up by six months at best. There would have been a cost savings, but again analysis of the detailed cost breakdowns for Apollo indicate the savings would have been on the order of 'only' $ 4 billion out of the NASA $ 18 billion project share. So in retrospect it would seem that NASA's management was correct, for the Apollo missions flown were much more capable than a Gemini-based approach would have been.

This was not the end of lunar Gemini. At least three times in the next four years such plans were again actively discussed.

September 1962 - Gemini Lunar Logistics and Rescue Vehicle

In the summer and fall of 1962 NASA headquarters asked Space Technology Laboratories and McDonnell to study use of Gemini as a 'lunar logistics and rescue vehicle'. The eight week study looked at using Gemini to land two men directly onto the lunar surface and identified the design changes required to accomplish this. An estimate was made of the cost of purchasing extra Gemini spacecraft for this purpose. But at that point in time Gemini was in deep financial and schedule problems, and the matter was not pursued further.

March 1964 - Gemini / Saturn IB

In the spring of 1964, with manned Apollo flights using the Saturn I having been cancelled, use of a Saturn I to launch a Gemini around the moon was studied. This could either be flown in the long gap between the end of Gemini and the start of Apollo/Saturn IB flights, or as a contingency to beat the Russians around the moon if Apollo suffered severe delays. But Von Braun and others were not interested in Congress getting wind of anything that could undermine support for Apollo. On June 8 NASA headquarters issued instructions that "any circumlunar mission studies related to the use of Gemini will be confined to in-house study efforts" and prohibiting issuance of contracts to McDonnell to pursue the matter.

June 1965 - Gemini / Double Transtage

Still the matter would not die. A year later, astronaut Pete Conrad conspired with Martin and McDonnell corporations to advocate an early circumlunar flight using Gemini. Discretely called 'Gemini - Large Earth Orbit', the plan would use a Titan 3C-launched Transtage to boost the Gemini to translunar speed. A declassified memorandum from the Director, Gemini Systems Engineering, documents a June 24, 1965 meeting at Manned Spaceflight Center between the contractors' corporate heads and highest NASA management. At this meeting the companies provided a detailed proposal to launch a refurbished, modified Gemini around the moon by April 1967 for $ 350 million. The Gemini would have 521 kg of mass deleted, half of it by removing the solid fuel retrograde rockets used to initiate re-entry (the liquid fuel Orbital Maneuvering System would be reengineered to increase its reliability). The Titan 2-launched Gemini would rendezvous and dock with a Titan 3C-launched 'Double Transtage'. The Double Transtage consisted of an unmodified first Transtage that would place itself and a second Transtage into low earth orbit. The first Transtage retained the navigation and maneuvering systems necessary to move the assembly to the rendezvous orbit with Gemini. The second Transtage would be stripped of unnecessary equipment (the orbital maneuvering system) but was equipped with an Agena-type docking collar.

After docking with the Double Transtage, the first Transtage would be cast off and the second Transtage would propel the Gemini into a circumlunar trajectory. The flights themselves, assuming go-ahead was given in September 1965, would follow immediately after the last Gemini flight. In December 1966 a Titan 3C would drive a 2450 kg circumlunar Gemini capsule to 11 m/s re-entry velocity to verify the heat shield design. This would be followed by a February 1967 manned qualification flight in earth orbit. A manned Gemini would dock with a Double Transtage and be propelled into a high orbit and re-entry speed. In April the sequence would be repeated, this time the Gemini being sent by Transtage into a loop around the moon.

The author of the memo thought that Gemini extension efforts would be better directed towards proving space station assembly techniques and procedures using Gemini and Agena. He also thought the schedule and cost estimates to be over-optimistic. The reaction of top NASA management was more categorical. Pete Conrad managed to stir Congressional interest, but NASA administrator James Webb informed them that any extra funds Congress cared to appropriate for such a project would be better spent accelerating the Apollo program. After further internal struggles, Conrad finally got NASA approval for the Agena on his Gemini 11 flight to boost him into a record 1,570 km orbit. This high flight was the only remnant of lunar Gemini.

April 1967 - Gemini Universal Lunar Rescue Vehicle

In the wake of the Apollo fire, NASA reexamined many safety aspects of the Apollo project. The Apollo mission profile was inherently risky, and the likelihood of a crew being stranded in lunar orbit or on the lunar surface was relatively high. McDonnell returned to a concept first studied in 1962 - the use of Gemini as a Lunar Rescue Vehicle. Use of the Gemini B capsule, then in construction for use with the US Air Force's Manned Orbiting Laboratory, with various combinations of Apollo lunar module stations, would provide a rescue vehicle that could pick up Apollo astronauts stranded in lunar orbit or on the lunar surface. Three variant rescue schemes were studied:

• Gemini Lunar Orbit Rescue Vehicle - This version could rescue an Apollo CSM crew stranded in lunar orbit. The Gemini would be launched unmanned on a translunar trajectory by a Saturn V. Following lunar orbit insertion it would automatically rendezvous with the disabled Apollo. The three Apollo crew members would transfer by spacewalk to the passenger compartment of the stretched Gemini re-entry module. It would then boost itself and the rescued crew to a transearth trajectory.

• Gemini Lunar Surface Survival Shelter - Prior to an Apollo moon landing attempt, the shelter would be landed, unmanned, near the landing site of the Apollo Lunar Module. In the event the LM ascent stage would not light to take the crew back to the Apollo CSM in lunar orbit, the two astronauts could go to the shelter and await a rescue mission. The astronaut in the CSM would return alone in the Apollo spacecraft.

• Gemini Lunar Surface Rescue Spacecraft - The unmanned Gemini spacecraft would be piloted by remote control to a landing near a stranded Apollo lunar module. An extended Gemini re-entry capsule had a passenger compartment for the two rescued astronauts. The basic LSRS design used three Lunar Module descent stages for lunar orbit insertion, lunar landing, and lunar ascent.

  An alternate configuration used two Apollo Service Modules and a repackaged LM descent stage. In the alternate configuration the first Service Module completed the translunar injection maneuver begun by the S-IVB stage; the second SM accomplished lunar orbit insertion and then functioned as a 'lunar crasher' stage, bringing the Gemini to just above the lunar surface. The Gemini and the third transearth-lunar landing stage would then hover to a landing near the stranded lunar module. The same final stage then boosted the Gemini capsule into a transearth trajectory.

McDonnell summarized the advantages of the various schemes, as contrasted with use of Apollo hardware for the same task, in the following matrix:

McDonnell concluded that an unmanned Gemini 'Universal Lunar Rescue Vehicle' could be developed that would perform all three tasks. The Gemini capsule would be extended to allow up to three rescued Apollo crew members to be returned. Such a craft could rescue the entire Apollo crew at any point along the Apollo mission profile. Some sketches appear to show a two-man Gemini crew in addition to three crew couches in the Gemini capsule extension. The unspoken point was that the Saturn V was in fact large enough to land men on the moon using the direct-ascent method. Use of lunar orbit rendezvous was only necessary because of NASA's adherence to the 6 metric ton, three-crew Apollo command module design. The 2 metric ton Gemini capsule, even in a form stretched to accommodate three to five crew, could accomplish a direct landing on the moon using Apollo components.

This last attempt to resuscitate Lunar Gemini failed as well. At that point in the Apollo program cut-backs already had begun. No funds would be forthcoming to build additional launch vehicles and spacecraft beyond those already purchased. There was definitely no money to provide a rescue capability, using either Apollo or Gemini hardware.

A Personal Postscript

Not considered at the time, but truly having the potential for a reduced-cost, reduced-risk program would have been a purely Titan-based, USAF-managed project. By using earth-orbit rendezvous and Titan 2 and Titan 3C as the launch vehicles, a program can be constructed that would have landed an American on the moon much earlier than Apollo. With a 2,500 kg open-cockpit LM the moon landing could be accomplished using only two Titan 3 launches: one a Titan 3E, putting a Centaur upper stage into low earth orbit; the other a Titan 3D, putting a Lunar Gemini-LM combination into low earth orbit, which would dock with the Centaur and then proceed to the moon. Such a program, taking into account the actual Gemini and Titan 3C development schedules, would have looked something like this:

Such a program could have achieved a manned lunar landing two years earlier than Apollo at half the cost, a savings of $ 9 billion.

References

• Baker, David, The History of Manned Space Flight,Crown Books, 1982.
• Hacker, Barton C. and Grimwood, James M.On the Shoulders of Titans - A History of Project Gemini, NASA, 1977.
• Hall, Edwin H., Memorandum to Deputy Director, Gemini Program, "Circumlunar Missions", June 29, 1965.
• McDonnell Douglas Briefing Materials, Universal Lunar Rescue Vehicle, April 1967.
• Many thanks to Tom Gangale for his thoughts and references on this subject, to Scott Lowther for discovering and providing the June 1965 memorandum, and to Mike Mackowski for uncovering details of the 1967 Gemini Universal Lunar Rescue Vehicle.