Designing a Bridge to the Moon

The Gemini program is often passed over in popular accounts of NASA’s race to the Moon. Perhaps understandably so. Gemini doesn’t carry the excitement of the Mercury Program with America’s first steps into space and it lacks the climactic excitement of the Apollo program with a lunar landing. The major accomplishments of the Gemini Program are usually highlighted in the greater scheme of the space race, such as America’s first extravehicular activity (EVA) or the first docking of two spacecraft. (Pictured is Gemini 7 in orbit as seen from Gemini 6. 1965.)

On the whole, however, Gemini is often treated like NASA’s overlooked middle child of the space race, a sad fate for the program I would argue is actually the most interesting of the era. As such, this promises be the first of several posts focussing on various aspects of the Gemini program. What fascinates me the most is that Gemini exemplifies the pioneering spirit and technological “go for broke” attitude NASA embodied in the 1960s. Even the genesis of Gemini is an interesting as it forced NASA to design a program in support of an as-of-yet- undesigned lunar program. The fundamental design choices of Apollo shaped Gemini.

In 1960, year after NASA’s first cohort of astronauts was selected and a year before the first of the inaugural Mercury missions flew, a follow-up program to Mercury was already in the works. The proposal came from director of the Manned Spacecraft Centre Robert Gilruth (right) who anticipated building on Mercury with a continuation of the program. The proposed program was designated Mercury Mark II and was a straightforward extension of Mercury with a two-fold application: furthering NASA’s understanding of spaceflight while also maintaining an American presence in space.

The initial Mercury Mark II goals were the same as Mercury with two modifications. In addition to continued research on orbital flight, man’s ability to function in space, and the safe recovery of spacecraft and astronaut were added long-duration spaceflight and pilot-controlled landings. These were two significant enhancements over Mercury, but not so unreasonable as to be impossible to achieve.

But in 1961, the game changed when Kennedy proclaimed the Moon to be the finish line of the space race. At the time, neither NASA nor the Soviet Space Program had the technology or the know-how to get to the moon, let alone land on its surface and walk around. This was a large part of the reason for Kennedy’s choice of the Moon: if neither nation knew how to get there, neither was ahead of the other. Having been beaten into space twice, first with Sputnik and then again with Gagarin, this new and lofty lunar goal gave NASA a chance to make up for lost ground.

The Moon as seen from Gemini 7 in Earth orbit. 1965.

Kennedy’s lunar goal also gave NASA a concrete goal, albeit a fairly distant and largely unknown one. The organization had a purpose and an end point. All that was left was to figure out how to get there. This had the effect of streamlining NASA in the shorter term. The Mercury program was underway and couldn’t be altered, but the proposed follow up program would now have to support the lunar goal; it was going to have to work out as many of the challenges associated with going to the moon as possible. It was going to have to become a bridge to the moon.

As early as 1961, with the Apollo program also on the drawing board, the decisions made supporting the lunar goal had a direct influence on the interim program. One of the most influential decisions for Apollo that shaped its predecessor program was the foundational decision of how the actual mission would unfold.

Three ways of getting to the moon, also called the mission mode, were given serious consideration. The first was direct ascent, whereby one spacecraft was launched directly to the moon, landed and returned home. The second was Earth orbit rendezvous, which required the spacecraft be assembled in Earth orbit before continuing on with a straight shot to the moon similar to the direct ascent proposal. A third option was lunar orbit rendezvous in which two joined spacecraft were sent to the moon, the smaller of which landed on its surface while the larger remained in orbit. (The third mode – lunar orbit rendezvous – is pictured in the schematic above.)

Another, less popular option was very briefly entertained: one-way mission whereby the astronauts would be sent to the Moon to wait until NASA could figure out a way to bring them home. This is not unlike current proposals for a one-way mission to Mars, only the lunar astronauts were not doomed to live out their days in an artificial environment. The method was crude to say the least, but at least it would ensure America triumph over the Soviet Union.

The final selection of a lunar mission mode ultimately came down to a matter of weight and simplicity. The first two proposals – direct ascent and Earth orbit rendezvous – required that the spacecraft be launched directly to the moon, a difficult endeavour. No launch vehicle had sufficient lift to send a spacecraft directly to the moon.

Both these proposals also required the same spacecraft to launch from the surface of the moon. Launching a spacecraft is a fairly intricate undertaking. Full countdowns are a complex but necessary procedure to ensure the working order of the spacecraft, launch vehicle, and all systems and subsystems. Launch pads are necessary to promote a safe and optimal lift off. To expect the astronauts to build a launch complex on the Moon, not to mention take all the required materials with them, was out of the question. Even if all the pieces of the puzzle were assembled in Earth orbit making the initial launches simpler, it would be difficult and dangerous for astronauts to build a launch pad on the Moon.

The simplest method of landing on the moon, and that which was eventually pursued, was the third proposal of lunar orbit rendezvous. Two smaller spacecraft launched at the same time would rendezvous and dock in Earth orbit before heading to the Moon. Once there, the smaller Lunar Module (LM) would land which the larger remained Command and Service module (CSM) in orbit. The LM has two separate halves, the lower descent stage and the upper ascent stage. Each stage had an engine, the descent stage to control landing and the ascent stage to relaunch from the surface using the descent stage as a launch pad. Without an atmosphere on the Moon, the landing craft didn’t need to be aerodynamically designed for a launch. A beautifully simple solution. (The image is an artist’s concept of the mated CSM/LM en route to the Moon.)

The complication of this method was the challenge of orbital rendezvous, a delicate manoeuvre that had to happen not once but twice in each lunar mission; the CSM and LM needed to be assembled in Earth orbit as well as in Lunar orbit. Rendezvous in Earth orbit was something that could be worked out in simple mission, but rendezvous in Lunar orbit was a different story. The effects of lesser gravity were impossible to really replicate in training. (Pictured is the view of a target docking vehicle, the Agena, as seen from Gemini 10. 1966.)

Thus, perfecting rendezvous and docking in Earth orbit became one of the primary goals of the Mercury Mark II program.

Another challenge facing the Apollo astronauts was the duration of a lunar mission. When Kennedy declared that the United States would land a man on the moon, NASA had less then fifteen minutes of suborbital flight under its belt, only five of which exposed the astronaut – Alan Shepard – to weightlessness. This five-minute period was the longest any Mercury astronaut had spent in zero-g; parabolic flights during training in the hollowed out aircraft gave the astronauts exposure to zero-g for about half a minute at a time.

Almost a year after Shepard’s flight, John Glenn became the first American exposed to a prolonged period of weightlessness. His three orbits around the Earth took about four hours. Carpenter, Schirra, and Cooper followed Glenn into orbit, with each flight lasting longer than the one before. The Mercury astronauts collectively racked up a little more than 50 hours in space – a little over two days combined exposure to weightlessness. It was going to take longer than two days to fly to the moon, land, walk around, take some samples and do some experiments, and fly home again.

A full lunar mission was estimated to take two weeks. And the crew couldn’t switch off. Apollo directors didn’t know how men would fare exposed to zero-g for fourteen days, so they had to find out. NASA had to ensure its astronauts’ vital functions wouldn’t be compromised after prolonged weightlessness. Would they be able to eat? After all, what was the point of going to the moon if the astronauts’ muscles were too weak to walk once they got there? Long-duration space flight became a second goal for the new program. (Pictured is the dehydrated food for “meal A” on Gemini 3. 1964.)

Starting a new program with Mercury Mark II also enabled NASA to move away from splashdowns, the landing method selected for Mercury. Splashdowns had proved to be a trade off. On the one hand, it was incredibly simple. The capsule fell through the atmosphere, protected from the friction by its ablative heat shield. A small drogue parachute deployed first to stabilize the capsule, followed by a main chute that slowed the capsule enough to allow it to make a soft landing in the ocean. The astronaut and capsule were then recovered by Naval forces.

On the other hand, splashdowns led to a complicated recovery. The required resources made it far from ideal. Two main detractors stood out: the hazards of landing in the water for both the astronaut and the capsule, and the astronaut’s total lack of control in the landing phase. Not relying on extensive Naval forces would simplify, as well as cut costs associated with, splashdowns significantly. (Left, Gemini 9 hits the water. 1966.)

A land landing system was ideal – the astronaut could control his own spacecraft without relying on a fleet of military attendants. Precision landings on land became another goal of the program.

In 1962, the program designation changed to reflect the stand-alone program that would iron out the wrinkles anticipated from Apollo. Mercury Mark II became Gemini in January 1962 with three clear-cut objectives: to achieve long-duration flight of up to two weeks in Earth orbit, to rendezvous and dock two vehicles in orbit using the vehicle’s own propulsion system, and to perfect the methods of pinpointing landings on land. Not officially stated but equally important was the goal of extra vehicular activity – the astronauts would have to function outside the safety of their spacecraft. There was no point in going all the way to the moon just to sit inside and look out the window. (Right, the iconic picture of Ed White during America’s first EVA or spacewalk. 1965.)

From the start, the end-of-the-decade deadline for a lunar landing put immense pressure on Gemini – there was no room for error and no choice but to progress as quickly as possible. The race to the Moon became as much a race against time as it was a race against the Soviet Union. The care taken with the first Mercury missions was not an option for Gemini.

NASA played it relatively safe with Mercury in a many ways, in large part because of the challenges associated with developing and man-rating new technology. The launch vehicle was particularly tricky. The Mercury program used two launch vehicles, the Redstone for suborbital missions and the Atlas for orbital missions. Both Intercontinental Ballistic Missiles were products of the Army Ballistic Missile Agency.

The Atlas missile was particularly problematic with its nasty tendency to explode during launch. The missile’s skin was so thin – not much thicker than a dime – that the pressure of the fuel inside was all that kept it upright. The missile body weighed about two percent of the fuel used to carry it into orbit. With this fragility in mind, NASA took great care before launching an astronaut. While ironing the wrinkles out of Atlas, two suborbital missions went up using Redstones. An Atlas launched John Glenn into orbit (pictured) within a year of Shepard’s flight. Glenn’s flight plan was subsequently repeated on the final three Mercury missions.

For all Mercury’s repetition, it made substantial leaps forward for NASA as its inaugural manned space program. Getting into orbit was a colossal feat, and doing it four times in a year was nothing to scoff at. NASA and America, it seemed, were poised for success in space. But at the same time Mercury’s in orbit yielded few other substantial gains.

NASA played it safe with multiple orbital flights following the same flight plan, but playing it safe wasn’t an option for Gemini. With the basics of spaceflight nailed down – launch, orbit, and reentry – the race was on for Gemini to work out all the kinks associated with a lunar mission as quickly as possible. And there was no room for error. With this tight time frame in the background, Gemini progressed at an impressive rate. No mission was repeated. As soon as one step towards a program objective was reached, the program moved on. With ten manned launches in twenty months, Gemini was the fastest moving program NASA has ever pursued.

Gemini yielded impressive results, largely related to the speed at which the program objectives were met. But the time pressures did have some negative effects on the program, notably killing some of Gemini’s technological innovations. The land landing goal was the only program objective that was left unmet – a fascinating story that is best discussed on its own.

Suggested Reading/Selected Sources

“The Gemini Program” – The John F. Kennedy Space Center. Revised March 10, 2004. [Accessed October 2, 2009].

Nancy Conrad and Howard Klausner, Rocketman. NAL. 2005.

Barton C. Hacker, and James M. Grimwood with Peter J. Vorzimmer. Project Gemini: Technology and Operations, NASA Historical Series. Washington: NASA. 1969.

Virgil I. “Gus” Grissom. Gemini: A Personal Account of Man’s Venture into Space. Toronto: The Macmillan Company. 1969.

Barton C. Hacker, and James M. Grimwood. On the Shoulders of Titans: A History of Project Gemini. Washington: NASA. 1977.

Barton C. Hacker, and James M. Grimwood. On the Shoulders of Titans. Scientific and Technical Operations Division, National Aeronautics and Space Administration, Washington. 1977.

David M. Harland. How NASA Learned to Fly in Space. Burlington: Apogee Books. 2004.

Chris Kraft. Flight: My Life in Mission Control. Penguin Putnam. 2002.

Gene Kranz. Failure is not an option: Thorndike Press. 2000.

David Shayler. Gemini: Steps to the Moon. Springer Verlag. 2001.

Wally Schirra. with Billings, Richard N. Schirra’s Space. Boston: Quinlan. 1988.

Deke Slayton. Deke!. Forge: New York. 1994.

Alan Shepard and Deke Slayton. Moonshot; Inside America’s Race to the Moon. Turner Publishing, Kansas City. 1994.


  • Stephane says:

    Among the “Suggested Reading/Selected Sources”, I would add Episode 5 -Spider-, of the documentary “From the Earth to the Moon” co-produced by Tom Hanks. It well describes the choice of LOR over other concepts. Actually, it would make sense to create an article dedicated to lunar landing methods :)

    • asteitel says:

      Stephane, you’re right to add “Spider” to the list. I am sort of saving it for a lunar landing methods post that’s in the works… It’s down the line, but it’s something I do intend to research more.

  • Pat Walsh says:

    A fascinating post. I agree that the Gemini program was indeed of far greater importance than popular histories credit, and also that the pressure on the program was quite intense. Given that pressure, I think NASA officials of that period are to be commended for the repetition that you note, as they tried to test every procedure and system and piece of equipment as best they could in the time they had.

    I also really like your title — in my book Echoes Among the Stars (2000, ME Sharpe Inc.), I also named the chapter on Gemini “A Bridge to the Moon.” :) And the most recent episode of my video series “Five Minutes in Space” (see is about Gemini 8 — in recognition of the 45th anniversary of the flight, on March 16, 1966.

    Thank you for this terrific site!

  • […] the 1960s. In the US, the programs moved at an alarming pace: Mercury quickly yielded the interim program Gemini, which paved the way for Apollo. As the end of the decade neared, NASA took increased risks with […]

  • […] methods and the Gemini program are two of my favourite topics, and I’ve previously posted about landing methods in Gemini. The […]

  • […] was already in its early developmental stages. More importantly, Gemini stood firmly in place as a necessary bridge between Earth orbital Mercury flights and the Apollo lunar […]

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