I have been watching From the Earth to the Moon, and just saw Part 4 which dramatised the Apollo 8 mission.

During Apollo 8 the crew placed themselves in orbit around the moon, for one day, and then returned to earth, using a single engine (on the SPS). A big deal was made in this episode about the possibility, but unlikelihood, of something going wrong with the engine, stranding the crew in lunar orbit.

I understand there was no planned contingency or backup system, but with all the people at NASA, someone would have been thinking what might be done in that case? If it didn't fire they surely wouldn't just sit there waiting for their oxygen to run out?

For example, did crew have suits that they could EVA with? (In the episode it was said that the fuel is self igniting and one "only" needs to open the valves.)

What would the procedures be, had the crew of Apollo 8 found themselves in lunar orbit with a non-responsive engine?

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    $\begingroup$ There were redundant sets of valves, triply so IIRC. A scenario where the spacecraft is generally healthy but the SPS fails to fire is incredibly unlikely; a more credible one would be if the Apollo 13 accident had occurred on 8, which would have been a bad day. $\endgroup$ Sep 27, 2014 at 0:52
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    $\begingroup$ I imagine that the 13 accident occurring on 10 also would have been a bad day, given that IIRC 10's LM was deliberately short on fuel (allegedly to discourage attempting to land). You'd have had the LM for backup like 13 had, but not the amount of fuel required to shorten the trip time the way 13 did after going around the moon (since that maneuver pretty much used up Aquarius' fuel), so you'd have been looking at the original travel time from the moon back to Earth. And of course they had no reason to carry restocking supplies for consumables, including oxygen. @pericynthion $\endgroup$
    – user
    Sep 28, 2014 at 17:12

2 Answers 2


This was one of the few scenarios where the Apollo program had no backup or abort available. If the SPS engine failed when entering lunar orbit, the spacecraft would just loop around the moon and head home. If it failed while exiting lunar orbit, they don't get to come home.

The other no-options situation was liftoff from the moon's surface. And Apollo 11 broke the ascent motor's breaker switch! They were able to reset it with a pen.

It's possible that minor failures could be fixed from inside the spacecraft, but it's difficult even today to service things in space unless they are specifically designed for servicing. How will you undo a fastener? Turning a wrench on a bolt will move you more than it will move the bolt. In the 1960s this was simply not possible.

NASA had a very quiet procedure for return-engine failure, and the Nixon administration had a draft speech written which was promptly filed-and-forgotten when everything worked.

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    $\begingroup$ Of course, the SPS was specifically designed with this in mind. From Apollo: The Epic Journey to the Moon, 1963-1972 by David West Reynolds, ISBN 9780760344521 page 214: "[The SPS] had -- this was the trick -- hypergolic fuels. Hypergolics were extremely difficult to deal with, but they were your friend when you wanted a sure-fire ignition. Hypergolic fuel ... will instantly explode on contact with its counterpart [component]. Tanks of the hypergolics were connected to the SPS in the simplest possible way, and all that had to happen was that the valves had to open.[...] Guaranteed ignition." $\endgroup$
    – user
    Sep 28, 2014 at 17:33

As noted in comments, the SPS ignition system was made extremely simple, with redundant valves and hypergolic fuel.

According to Chaikin's "A Man On The Moon", the astronauts asked for some sort of manually actuated valve system in addition, and didn't get it; in this case the additional weight and complexity was judged unnecessary, and the small risk of multiple valve systems failing was considered acceptable.

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    $\begingroup$ The manual system was basically the lever and cable arrangement that works the brakes on your bike. $\endgroup$ Oct 6, 2015 at 14:33
  • $\begingroup$ That would be an amazing way to fly a rocket ship. :) $\endgroup$ Oct 6, 2015 at 14:51
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    $\begingroup$ I vaguely recall that a few bits of the manual system were actually there, but a spacewalk to the engine bell would have been required to open the valves as the linkage was not. I have to admit this sounds like a bad idea, but when no other options remain bad ideas start looking like good ones. $\endgroup$
    – Joshua
    Oct 24, 2018 at 14:39

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