The Lunar Module had an abort mode where the crew basically just had to push the ABORT button on the control panel, and the ascent stage would detach from the descent stage, followed by the ascent stage engine igniting to take them away from the descent stage and -- hopefully -- ultimately back into lunar orbit.

That would have worked nicely during the descent, when gravity would have done a good job of getting the descent stage out of the way, but the recent discussion on not being able to take off after landing made me curious. What would happen if, after landing, the crew got into (or remained inside) the LM, performed all relevant pre-launch steps, and pushed the ABORT button? We are of course assuming here that one of the steps performed would be to arm the ascent engine.

  • Would the LM's computers (PNGS or AGS) have allowed such an "abort"? Or was there some lock-out that prevented aborting after touchdown? (I'd like to think that aborting was one of the options available to the crew with the fewest things that could go wrong.)

  • How would it be similar or different compared to a normal ascent launch? Are there scenarios where one approach might have worked for getting them off the lunar surface, but not the other?


1 Answer 1


After a nominal landing the crew is waiting for a go from the ground to stay on the Moon. This was called the "Stay/No Stay for T1" and meant that there were no imminent issues requiring an immediate launch. So it was a commitment to stay for at least a few more minutes, until Mission Control could do a more detailed evaluation of the Lunar Module systems. If they didn't receive this Stay, then they would have used the Abort Stage button and the ascent abort programs of the AGC. So a procedure that is essentially identical to an abort before touchdown.

After this Stay for T1 was received, the landing confirmation program (Program 68) is called on the AGC. After having started P68 you can't go back to using the ascent abort programs (Programs 70 or 71). Instead the nominal ascent program (Program 12) would have been used. And in fact Program 12 was nominally called directly after P68, in preparation for a launch.

After the more detailed systems inspection I mentioned there was another Stay/No-Stay poll. If they didn't receive a Stay at this time, they would have launched with Program 12, just like a nominal ascent, although with slightly different insertion conditions.

Some more things about the Abort button. It's actually two buttons, Abort and Abort Stage. The Abort button mostly sends a signal to the AGC (PGNS) and the AGS that an abort with the descent stage engine is desired (using Program 70 of the AGC). The Abort Stage button both causes staging and sends a signal to the AGC and AGS that an abort with the ascent stage engine has to be started (Program 71). The Abort Stage button was also used to arm the staging pyros for a nominal ascent. Alternatively there is a "Staging Fire" switch, which also can separate ascent and descent stage.

The crew procedure for this can be found in the LM Timeline book, this one was for Apollo 12: https://history.nasa.gov/afj/ap12fj/pdf/a12_lmtb.pdf on page 5 and 6.

  • 3
    $\begingroup$ Good point on the Abort and Abort Stage buttons being separate. I was hoping to keep the question slightly simpler by glossing over that detail. $\endgroup$
    – user
    May 28, 2017 at 13:59
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    $\begingroup$ They actually took some care to make the poll STAY / NO STAY (as labeled in the flight plan you linked) to avoid any confusion over whether go means stay, or go means leave. $\endgroup$
    – hobbs
    May 28, 2017 at 15:29
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    $\begingroup$ Thank you, Margaret Hamilton. I can just imagine how it would have looked like on TV if it had happened while Neil was going down the ladder. $\endgroup$
    – SDsolar
    May 29, 2017 at 5:26

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