5
$\begingroup$

In the event of the loss of all fuel cells in an Apollo mission, would reaching orbit with the third stage, then using the relight to de-orbit somewhat near the normal location in the pacific be a reasonable plan?

Full scenario: something like the Apollo 12 lightning strike, but the CM-SM electrical connections fail outright due to overvoltage. It's plausible with a good Saturn V, mission control might opt to get into orbit to run diagnostics. On finding they can't get any power out of the service module need to return would be inevitable. To my mind, trying for more than about 45 minutes would be rather silly. I couldn't get a good estimate on the CM endurance on battery but I wouldn't want to push it.

I came up with the following possible de-orbit plans.

  • Ignite third stage to de-orbit, then SM-Jett to get rid of the third stage, depend on the RCS backaway to get separation.

  • Ignite third stage to de-orbit, then SM-Jett, turn 90 degrees and use the third start (according to the manual the third stage has three starts though only two were ever used on any mission) to get a lot of separation.

  • Use the propulsive fuel jettison on the third stage to de-orbit. This has the potential advantage of the third stage being light enough to use the third stage's auxiliary propulsion system to get separation (it can't thrust backwards so a turn is necessary).

  • Separate from the third stage and use the SM engine to de-orbit. We don't have to worry about the aux fuel pumps to get fuel from the secondary tanks as this will be the only burn. Note that this subsystem may not be working because of the damage above.

  • Try a TDE to get the lunar module so you can use its resources (including engine) and de-orbit whenever you want. Depending on the disaster, service module RCS may be unavailable, and you can't do a TDE with CM RCS because it can't thrust forward. (TDE using Third Stage APU is too dodgy to consider unless everything else is already hopeless.)

Would any of the third-stage plans have been actually feasible or is getting to orbit with no power from the service module the kind of thing that must be avoided in the mission plan? That is, had the SCE to AUX switch been unreachable from anybody's seat been an abort scenario because waiting to get to orbit been too risky of a situation to be in?

$\endgroup$
4
  • $\begingroup$ Interesting question; a brief check over the Apollo abort modes doesn't show any plan for the SM failing. My guess is that rather than going to orbit, they'd have tried cutting off the ascent burn, jettisoning the CM, and trying to maneuver it away with the CM RCS. That's not based on anything more than a gut feeling, though. $\endgroup$
    – DylanSp
    Dec 20, 2021 at 1:49
  • 5
    $\begingroup$ @DylanSP per Apollo flight rules you'd have to lose all 3 fuel cells plus one of the batteries to call an ascent abort. space.stackexchange.com/a/28411/6944 $\endgroup$ Dec 20, 2021 at 3:40
  • $\begingroup$ Joshua, can you clarify what scenario you have in mind? Loss of 3 fuel cells is one thing, total loss of electrical connection between the CM and SM is another. $\endgroup$ Dec 21, 2021 at 17:48
  • 1
    $\begingroup$ @OrganicMarble: Lightning bolt fries the power lines between CM and SM. Doesn't matter how many working fuel cells you have you're not getting any power from them. $\endgroup$
    – Joshua
    Dec 21, 2021 at 17:57

0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.