What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)

238,000 miles from home — Earth as viewed by the Apollo 8 astronauts in lunar orbit, Christmas Eve 1968. Image credit: NASA.
The three-man crew of Apollo 8 — Commander Frank Borman, Command Module Pilot James Lovell, and Lunar Module Pilot William Anders — was the first to leave Earth on a giant Saturn V rocket. They departed Cape Kennedy, Florida, on 21 December 1968, and left Earth orbit for the Moon about two and a half hours after launch.

Though its target was the Moon, the Apollo 8 mission included no Lunar Module (LM). The piloted lunar lander had suffered production delays, which was understandable given that no one had previously built a vehicle for landing humans on another world.

NASA's planned mission sequence for piloted Apollo missions had begun with a low-Earth orbit (LEO) test of the Command and Service Module (CSM) during Apollo 7 (11-22 October 1968). This was to have been followed immediately by an LEO test of the CSM and LM, then a CSM/LM test flight in higher Earth orbit. During the fourth mission in the sequence, astronauts would test the CSM and LM in lunar orbit, then the first Apollo lunar landing attempt would take place. NASA designated these five increasingly ambitious missions C, D, E, F, and G.

Putting off the next Apollo flight — the D mission — until the LM was ready might have placed in jeopardy attainment of Apollo's goal of landing a man on the Moon ahead of the Soviet Union and before the end of the 1960s. Because of this, in late summer 1968, NASA began to look at a modified mission sequence.

The C' mission, which would see the Apollo 8 CSM orbit the Moon without an LM, was revealed to the public on 12 November 1968, three weeks after Apollo 7 successfully accomplished the C mission. Apollo 8 would test many CSM elements of the lunar landing mission and the world-wide system of radio dishes and transceivers NASA had created for Apollo lunar mission communications and tracking.

The C' mission had been the subject of intense debate at the highest levels of NASA, for it meant traveling to the Moon without the backup life support and propulsion systems the LM could provide. Intelligence reports that indicated that the Soviet Union might launch a man around the Moon during December 1968 gave C' supporters added credibility. The Soviet mission might steal Apollo's thunder; though it would merely swing around the Moon and fall back to Earth, it would enable the Soviets to claim that they had launched a man to the Moon first.

Eleven hours after launch, the Apollo 8 crew carried out a course correction. This required that they ignite the CSM's Service Propulsion System (SPS) main engine for the first time. Had the SPS not functioned as planned, the crew could have adjusted their course using the CSM's cluster of four Reaction Control System (RCS) thruster quads. The CSM would then have swung around the Moon without entering orbit and fallen back to Earth.

Partial cutaway of Apollo CSM spacecraft. Image credit: NASA.
The 20,500-pound-thrust SPS, an AJ-10-137 rocket engine manufactured by Aerojet, was located at the aft end of the CSM. Other AJ-10 variants had propelled Vanguard, Atlas-Able, and Thor-Able launch vehicles.

The SPS burned hydrazine/UDMH fuel and nitrogen tetroxide oxidizer. Chemically inert helium gas pushed the propellants into the engine's ignition chamber. Hydrazine/UDMH and nitrogen tetroxide are hypergolic propellants; that is, they ignite on contact with each other. The resulting hot gas then vented through a large engine bell, which was designed to swivel to help steer the CSM.

The Apollo 8 SPS performed almost perfectly during the 21 December course correction burn and during a second burn 61 hours after launch. Three hours later, Mission Control in Houston gave Apollo 8 a "go" to enter lunar orbit. The spacecraft passed behind the Moon, out of radio contact with Earth, and the crew ignited the SPS for the third time. It burned for a little more than four minutes, slowing the Apollo 8 CSM enough for the Moon's gravity to capture it into orbit.

The Apollo 8 CSM orbited the Moon 10 times over the next 20 hours. Then, on 25 December 1968, about 89 hours after launch, the crew ignited the SPS behind the Moon to begin the journey home to Earth. The rocket motor performed flawlessly during the critically important burn, which NASA dubbed Trans-Earth Injection (TEI).

Two and a half days later, on 27 December, the CSM split into two parts. The Service Module (SM), which included the SPS, separated from the Command Module (CM), which held the crew. The former burned up in Earth's atmosphere as planned, while the latter, protected by a heat shield, maneuvered in the upper atmosphere to reduce heating and deceleration, deployed parachutes, and splashed safely into the Pacific Ocean.

Four days after Apollo 8's triumphant return, A. Haron and R. Raymond, engineers with Bellcomm, NASA's Washington, DC-based planning contractor, completed a brief study of what might have happened had the SPS not ignited for the TEI burn. Specifically, they looked at how long a crew might survive in lunar orbit following a TEI failure.

Haron and Raymond found that the "first constraint" on the crew's endurance would be depletion of the CSM's supply of lithium hydroxide (LiOH) canisters. The square canisters were used in pairs to remove carbon dioxide exhaled by the crew from the CSM's pure oxygen atmosphere. During Apollo 8, the crew traded a saturated LiOH canister for a new one every 12 hours, so expended two per day.

The Bellcomm engineers calculated that, at that rate, the crew would use up the last of the 16 LiOH canisters launched on board the CSM 96 hours after TEI failure. They would then grow drowsy and become unconscious as carbon dioxide accumulated in the crew cabin. Had TEI failed on Apollo 8, Borman, Lovell, and Anders would probably have suffocated on 29 December.

Haron and Raymond noted, however, that LiOH canisters might be changed less often without harming the crew. They cited a November 1968 Manned Spacecraft Center study that showed that a LiOH canister could absorb carbon dioxide for up to 37 hours. If a stranded Apollo CSM crew began to ration its LiOH canisters immediately after TEI failure, they would be able to stretch their survival time to 148 hours. In that case, the Apollo 8 crew would have survived until New Year's Eve – the day Haron and Raymond completed their study.

By that point, limitations on crew survival other than carbon dioxide buildup would begin to come into play. The CSM fuel cells, manufactured by Allis Chalmers, operated by combining liquid hydrogen and liquid oxygen reactants to produce electricity and water. Electricity from the fuel cells powered the CSM through most of the mission. The crew drank the water, which also was used for cooling the CSM's Environmental Control System (ECS) and electronics. Excess water was dumped overboard.

Haron and Raymond looked briefly at the possibility of switching off two fuel cells to conserve reactants. If this were done, then the remaining fuel cell might operate for up to three weeks after TEI failure. However, a single fuel cell would probably not produce enough electricity to operate all CSM systems vital to the crew's continued survival, some of which were not immediately obvious.

As an example, Bellcomm cited the RCS quads. The astronauts would need to use them to maneuver the CSM to keep its ECS radiators in shadow to conserve cooling water. In addition, the LiOH canister shortage would remain. "The feasibility of extending survival time to as much as three weeks cannot be confirmed at this time," Haron and Raymond wrote.

The Bellcomm study was mainly of academic interest; a crew stranded in orbit around the Moon, 238,000 miles from Earth, could not have been rescued even if they did survive for three weeks. NASA did not have the ability to maintain a rescue Saturn V rocket and CSM on standby.

The space agency would have cause to recall the brief Bellcomm study twice during subsequent Apollo missions. During Apollo 13 (11-17 April 1970), an oxygen tank exploded in the CSM Odyssey, badly damaging its SM.

Because the explosion happened while the mission was en route to the Moon, its crew, commanded by Apollo 8 astronaut James Lovell, was able to use the LM Aquarius as a lifeboat. The astronauts employed the LM descent engine in place of the SPS. The docked spacecraft flew behind the Moon, where the crew fired the descent engine to adjust their course and accelerate toward Earth.

During Apollo 16 (16-27 April 1972), as the CSM Casper orbited the Moon, it suffered a malfunction in the system meant to swivel its SPS engine bell. The LM Orion, which had already undocked in preparation for landing, stood by in lunar orbit until the SPS problem was understood, then landed several hours behind schedule.

Had it been judged necessary, NASA could have scrubbed the Apollo 16 landing. Orion would then have redocked with Casper. The astronauts could have used Orion's descent engine and (if necessary) Casper's RCS quads to perform TEI.

Proceeding with the landing eliminated that option; the descent engine used most of its propellants to land on the Moon, then was left behind on the surface with the rest of the LM descent stage. The LM ascent stage, with its smaller engine, returned to lunar orbit with virtually dry tanks. This left only the SPS available for TEI.

As a precaution, NASA moved up Apollo 16's TEI burn by a day in the hope that, should the SPS misbehave, the crew and engineers on Earth would have adequate time to find a solution and ensure a safe, if delayed, return to Earth. As it turned out, the Apollo 16 SPS performed a flawless TEI burn.


NASA News Press Kit, Project: Apollo 8, 15 December 1968.

"Consumables Affecting Extended CSM Lifetime in Lunar Orbit," Case 320, A. Haron and R. Raymond, Bellcomm, Inc., 31 December 1968.

Apollo 8: "A Most Fantastic Voyage," Lt. Gen. Sam C. Phillips, National Geographic, May 1969, pp. 593-631.

Apollo 13: "Houston, We've Had a Problem," NASA EP-76, 1970.

NASA Mission Report: Apollo 13, A Successful Failure, 20 May 1970.

How Apollo Flew to the Moon, W. David Woods, Springer Praxis, 2008, pp. 236-238.

More Information

What If an Apollo Lunar Module Ran Low on Fuel and Aborted its Moon Landing? (1966)

What If an Apollo Saturn Rocket Exploded on the Launch Pad? (1965)

"Assuming That Everything Goes Perfectly Well in the Apollo Program. . ." (1967)


  1. Ben:

    NASA never seriously considered circumlunar Gemini, though the concept was studied along with so many others. As I recall, Pete Conrad was a fan of the concept. Astronauts in those days had enough clout to get studies of their pet projects done, but that didn't mean anyone would sanction hardware development and flight. Jack Schmitt's Tsiolkovskii mission was another example.

    The USSR flew a bunch of modified Soyuz circumlunar spacecraft under the designation Zond ("probe"). These never carried a crew. Zond was Soyuz without an orbital module. They launched on Proton rockets with a fourth stage for circumlunar injection. Many (perhaps most) never made it to orbit. Proton, roughly equivalent to the Saturn IB, was new and cranky, so blew up on the way to space. Others flew around the moon, returned to Earth, and failed to complete the skip maneuver that would land them in the USSR. They splashed into the Indian Ocean instead after high-deceleration ballistic reentries. The Australians managed to photograph one during recovery in the Indian Ocean. At least one depressurized, killing its cargo of animals.

    As I recall, only one Zond performed as planned. I haven't been well the last few days, so will leave it to you to look up the details. Also, at least one was flown after Apollo 8. As I recall, Zond 8 was the last in the series, though a Zond 9 was planned and scrubbed.

    Hope this helps.


  2. Ben:

    Your comment made me laugh - I only rarely follow sports, so I have no idea what your "New England Patriots" reference means. My late wife joked that I have the popular culture knowledge of a turnip. I always thought that was insulting to turnips. I miss her occasional "what is happening in mainstream culture" briefings.

    But anyway, your points 2 and 3 are spot on. I think people underestimate the difficulties and unknowns and overestimate our capabilities. Spaceflight isn't a science fiction movie: it's hard, as I've heard said a lot lately. It's especially hard when we make dumb choices, develop odd beliefs about what is feasible, don't school ourselves as to the real nature of the challenges, and don't spend enough money. 1% of the Federal budget - rather than half of 1% - would enable NASA to do many things.

    Apollo was tailored to accomplish JFK's mandate. LOR was not a great mode if one wished to make the moon a permanent part of human activity - a new continent, as it were. It was good for getting to the moon fast and relatively cheaply. EOR or Direct Ascent would have been better if we had intended to establish a permanent presence. In fact, a high-level NASA planning report from 1966 - the last year it was possible for bigwigs within NASA to convinces themselves with reason that Apollo was only the beginning - saw NASA evolve Apollo back to Direct Ascent by the end of the 1970s. I was looking at that the other day - need to write about it.

    That's not to say that Apollo wasn't an awesome achievement. It absolutely was, but it was limited by the technology of its era and the political mandate that made it happen.


  3. Just for fun: The real football is soccer. At American Football the players can use their hands. Is that football? US citizens are still funny, it's like using miles, inches, gallons, ... much more. No one outside of the US will ever understand the culture.

    But more serious to David:
    You said "EOR or Direct Ascent would have been better...". I disagree on this statement because landing a man on the moon never would have happened. Only if there were enough money I would combine all three methods together:

    EOR: We have the ISS which could be used as a factory and propellant base. A launch to that height is relatively cheap.

    LOR: A base around the moon at the Lagrangian point L2 (straight behind the moon from earth) would have many advantages. At an elliptical orbit around L2 you would see the far side of the moon, but also always the earth. And this could be the second fuel station. Landing man on the moon and bring them back to that point would need not that much energy.

    Direct Ascent: The best option to launch big devices from earth to the moon with no requirements to come back.

    But that's all Since Fiction, not because it's not possible but because there is no money for that.

  4. To get back to Ben's question: There were indeed only two (unmanned) Zond missions that managed circumlunar flights before December 1968, along with five more that . . . didn't manage that much. Zond 5 managed the feat in September 1968, returning some Russian tortoises alive, though its failed skip reentry would have been rough on any cosmonauts. Zond 6 in November managed to depressurize on reentry and kill the animals on board, and suffered a parachute failure to boot. Given this track record, one can understand why even the Soviets were reluctant to risk human beings at that point.

    Yet U.S. intelligence, and thus NASA, did not know all of that. The Soviets did not publicize their failed Zonds, and represented Zond 5 and 6 as having gone according to plan. Everything pointed to the Soviets attempting a manned Zond within the next few months. And there's evidence now to suggest that, even with all the setbacks with the Zond capsule and the kludgy Proton booster, the Soviets came very close to attempting a manned Zond flight in December shortly before Apollo 8, in a desperate attempt to beat the Americans to circumlunar space. In a 2004 issue of Quest magazine, Peter Pesavento and Charles Vick took a close look at the Soviet lunar programs, and given access to newly declassified documents, uncovered a number of items that point to such an attempt, including the following:

    Studying declassified Corona spy satellite photographs, Vick is able to show that there was substantial unexplained activity at the Baikonur cosmodrome during December 1968. Although no photographs exist during the 8-12 December launch window, images made during a pass on 15 December show a Soyuz spacecraft - booster combination mounted on its pad and the Proton pad gantry in position, although no booster is mounted. A week later, the Soyuz booster is being removed from its pad, but now a Proton - L1 combination is on the Proton pad. This seems to clearly indicate that attempts were being made, right up to and beyond the day Apollo 8 was launched, to beat the Americans to the moon. The authors theorise that an attempt at a manned launch to the moon using the two-launch podsadka scenario was attempted, but that some serious spacecraft problem must have resulted in the Proton launch being scrubbed.

    So the fear of being beaten to the punch - especially in light of so many other Soviet firsts over the previous decade - was a legitimate one, even in light of the numerous problems with the much less mature Soviet lunar programs (some of which NASA only later learned about). And had there been another significant setback for Apollo (and the delay of Grumman's LM was threatening to become exactly that), it's possible to posit that the Soviets might have been in a position to attempt a manned Zond flight by spring or summer (though it would have been a risky one).

    And a manned circumlunar Zond flight was the only real shot the Soviets had of beating the U.S. to the Moon in any phase by that point. Its program for a manned landing (and obviously also lunar orbit), the N1/L3, was at best still a few years from being feasible.

  5. All the Soviet firsts in space is a myth. First science in space was done by the US, not Sputnik or Laika (poor dog). And the first orbital flight could have been accomplished in September 1956, if ABMA would have been granted to do so.

    The first manned flights by the soviets were much more risky and they had many luck not loosing a cosmonaut. And when NASA did start Gemini the soviets had been far behind.

    At the Zond program was only one flight where a human could have survived. And the N1/L3 was not feasible from the beginning. There was no test stand for the first stage, the failures instead tock place on the pad destroying the entire rocket.

    1. All the Soviet firsts in space is a myth.

      It may have been overwrought, but it wasn't entirely a myth. From the moment Sputnik launched, the Soviets demonstrated a substantive lead in heavy lift, one which they kept through the mid-60's. And there were firsts: first satellite in orbit. First probe in in circumlunar space. First probe impact on the Moon. First soft landing on the Moon. First lunar satellite. First man in space. First man in orbit. First woman in space. First spacewalk. First manned docking in space.

      Some of these may be glossed as stunts, often very risky stunts, ones with very little scientific return. But in politics, perception becomes reality. And the perception was that, until late in the Gemini program, the U.S. was behind the Soviets in space exploration capability - and the perception wasn't really erased until Apollo 8.

      I won't disagree much with your characterization of Zond or N1/L3. It appears that a Zond/Posadka mission *could* have had a good chance at a successful manned circumlunar flight by the end of 1969 had the Soviets kept at it, rather than giving up after Apollo 8. Of course, such a capability was a dead end; For lunar orbit or lunar landing, N1/L3 was what they had to use, and it was a program with massive problems. I think they were on the way to making N1 feasible by 1972, but there was no political backing to keep working on it by that point. The problem was that the Soviets simply committed too late to a serious lunar program, and failed to centralize and harmonize those efforts once they did - in stark contrast to Project Apollo.

    2. P.S. I don't want to overly characterize the apparent scrubbed Soviet Zond mission in December 1968; we don't know exactly why it was scrubbed, or even how close to came to being approved; all we know is that the Soviets were trying, right up to the last minute, to the point of getting a mated booster and capsule to the launch pad. And indeed, out of seven test missions to date, only one was successful enough to have been survivable by cosmonauts (and that would have been a bone-rattling experience). Not an encouraging track record.

      Of course, the U.S. didn't know all of that; they believed the Soviets had managed two swimmingly successful unmanned circumlunar flights (two more than the U.S. had managed), and looked like they were going to try another in their December launch window, one which might include cosmonauts. They had good grounds for perceiving themselves in a tight race to the Moon, one which they might lose.

      Ben's original question is harder to answer. The Soviets did manage two successful circumlunar Zond flights (Zond 7 & 8) later in 1969; it is not unreasonable to think that, had the will been there, they could have managed a manned Zond flight to the Moon that year. But after Apollo 8, they had little incentive to do so. Had Apollo run into further delays - had the LM been further delayed and NASA opted to hold off on any further flights until it was available - I think it is not inconceivable by that the Soviets might have pulled off a high risk manned Zond flight in the summer of '69, beating the U.S. to cislunar space.

    3. It baffles me (I understand the political why, but still...) why the Soviets in their plodding method like they did for space stations, did not go and at least orbit the Moon and operate there after Apollo.

      Conflicting agendas. Lack of clear direction from the political leadership. Ironic from a centrally planned economy - dictatorship, not to put too fine a point on it - but such was the nature of the space program in the USSR, which had to navigate the purge of one regime (Khrushchev) and another that permitted competing space organizations with not only different architectures, but even different objectives.

  6. My thoughts on all the "Firsts":

    First satellite in orbit: Beep-beep, no science. And ABMA could have launched Explorer 1 a year before.

    First probe in in circumlunar space: Lunik 3 did miss the moon by more then 6,000 kilometres.

    First probe impact on the Moon: The first pictures were done by the Ranger program on a mission profile like this.

    First soft landing on the Moon: Luna 9 was successful. But Surveyor 1 was only three months later and also successful.

    First lunar satellite: I can't see this. The first US orbiter was Lunar Orbiter 1.

    First man in space. First man in orbit: High risk, NASA did a suborbital flight only three weeks later.

    First woman in space: And the last for a long time. This did not open space for women, it was just propaganda.

    First spacewalk: Alexey Leonov had serious problems. Ed White did it much better a few weeks later.

    First manned docking in space: Soyuz4/Soyuz5 did this in January 1969. By that time many dockings have happened at Gemini and Apollo 8 was orbiting the moon.

    Why all the firsts done by the US are so minor?
    First fluid propelled rocket (Goddard), first successful launch of a captured V2 after WWII, first space plane (X-15), first picture of the earth from space, and first science in space (Van-Allen-Belt).

    1. Well, if you really want to get down to it, Apollo itself was really just a stunt of sorts, too, wasn't it?

      To be blunt: a flags-and-footprints program, designed with the sole objective of not only putting a man on the Moon and returning him safely to the Earth before an arbitrary deadline, but doing so before the Soviets did, too. Any science that might be extracted from it was a distinctly secondary consideration., How could it be otherwise for an architecture designed to spend only a pathetic single day on the lunar surface (later expanded to a measly three)?

      That's not to say there wasn't real science done on Apollo - especially on the J class missions. There was. But it had to be done in an architecture really not designed for it, and that's why there was so much disgruntlement about it in the space sciences community. Had it been followed by by AES or LESA, now, that would have been a science-centered mission architecture. But all that had been killed off even before Apollo 11 touched down on the Sea of Tranquility.

      And the same was true of so many of the U.S. "firsts" and "seconds" after 1957, too. How much science was really done by Mercury and Gemini? How much was really done by Ranger?

      I'm not really disputing your basic point about the Soviet firsts being mostly stunts, almost always quickly followed by more impressive, better engineered U.S. follow-up. It's just that this was really the nature of the Space Race, by and large. Yes, some good science was eventually done along the way, more by the U.S., but it was almost always a secondary consideration. It was a political contest. And in that contest, perception was the reality.

      P.S. The first lunar satellite was the USSR's Luna 10 in April 1966. The U.S. Lunar Orbiter 1 came four months later, in August 1966.

  7. How much science was really done by Mercury and Gemini? How much was really done by Ranger?

    Truly the science in these cases was engineering. Could we put all these parts together and make them work in the most hostile environment ever tried? Apollo, with some trial and error (Apollo 1, Apollo 13) basically proved repeatability of experiments of flying people to the Moon. Simple goal, but a really complex operation. The complexity, and getting it to work more than once was the science. They did this stuff with SLIDE RULES! Which is just plain crazy. Your iPhone has more computing power than NASA did in the 60s.

    Oh, yeah, and the components were provided by the lowest bidders. Wow.

    1. Oh, no question - the engineering accomplishments of the Space Race - the manned programs and the probes of the various NASA labs - are simply staggering. It still astounds me that we could go from Explorer to Apollo 11 in just 11 years using...well, slide rules. That the Apollo CSM main computer could travel a half million mile round trip and enter and exit lunar orbit with precision with less than 50k of RAM.

      Still that's all applied science, not pure science. Both the U.S. and Soviet programs were designed and funded primarily as political contests, not scientific research.

  8. Seems I've been missing out on a very interesting discussion. Sometimes I regret writing this blog because it means I have to move on and let the comment be at some point or nothing gets written. But then if I didn't write the blog there'd be no comments. This circularity gives me a headache.

    The lunar science community in 1961 comprised kooks and some very talented people. The first big lunar/space science planning meeting in Iowa City had about 100 participants. And of course the goal was geopolitical, not scientific. Yet through the persistent efforts of the scientists and NASA's perceived need to make Apollo look less like a stunt than it was, we managed some terrific science. Without meaning it, the moon program laid the groundwork for subsequent Solar System exploration in the 1970s and after. And, after Apollo, no one could say with certainty that any mission was impossible in space.

    It was a Cold War victory, ephemeral like so many of them, it was extremely costly for the amount of science (or anything else) it produced, but it had a long-range impact that is hard to overestimate, I think.



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