|Quoting Ba97 (Reply 10):|
This leads me to a somewhat off topic question. Knowing the delicate nature of targetting the moon orbit and how a degree of slippage could be death, I was thinking of the horrific situation occurring that if the command module shot/wandered off into space and control back into a lunar or revised earth orbit (i.e. the trajectory of the shot to the moon was an elongated orbit so a reverse of that) was not happening, did NASA have a procedure/protocol? I can understand the concept of the issue of being trapped on the Moon and slowly losing air, food in total communication with earth. How far out would communications from earth extend to the command module as it drifted away?
Quite a ways. I don't have an exact number, but some amateurs listened in on Apollo radio signals from the moon with a 9m dish back during Apollo 17. That had pretty good SNR
(over 40dB, IIRC). Numerous other amateur radio astronomers picked up signals from the various Apollo missions.
But, assuming some proper gear, for example, the Parkes observatory in Australia, which was one of the stations used for monitoring Apollo, was a 64m dish, which would have been able to pick up the same signal as the amateur’s 9m dish at seven times the range. We can probably take that as an absolute minimum range at which that NASA could have communicated with an Apollo.
Add to that the maximum velocity Apollo could have achieved would be only about 6-7000mph* more than escape velocity from earth, so they wouldn't have been leaving all that fast, and it would have taken eight or nine days to reach that minimum distance, at which point you're pretty much running out of life support.
Of course that's totally unrealistic, and you'd only manage that sort of trajectory by deliberate action. In practice the S-IVB gave them all the push they needed to get to the moon, and there was only a single (small) SM
burn to fine tune that.
The S-IVB *could* have pushed the Apollo stack out of earth orbit (not just over the hump into the moons gravity well, which required less energy), but at a pretty slow pace - weight growth on the bits of Apollo pretty much maxed out the S-V for the lunar mission as it was. Had a completely cockeyed S-IVB burn happened (that somehow *didn't* get stopped before the S-IVB ran dry), they'd have immediately dumped the S-IVB, probably the LM
(unless they wanted the lifeboat option), and used the SM
put send themselves back to earth - it would have had more than enough capacity to do so following any conceivable S-IVB burn from LEO. Then you'd need a completely wrong direction SM
burn to get the high exit velocity. An SM
failure at that point would, of course, be a huge problem.
Realistically, a really bad S-IVB burn would have been stopped long before that point. Even if they did almost all of the planned burn length needed to get to the moon, that would leave the Apollo at less than escape velocity (although at the high end of that, it would have been a pretty long elliptical orbit).
A rather bigger risk was pooching the return trajectory so that you miss the earth or skip off the atmosphere (or missing the other way and entering too steep). In the former case, you'd pass by the earth at near escape velocity (but a bit below, probably), but you'd be stuck on a week-plus elliptical orbit before you came back, and you'd be long out of life support at that point. In the later case, the return might not be that long, but life support is very minimal at that point (only the batteries and tanks in the CM
, after call), and there's no real ability to maneuver anyway at that point (since the SM
is gone), and again, you'd run out your life support, unless you managed to scrub off enough velocity during the skip, but then you'd almost certainly do a really bad reentry.
*Assuming a semi-normal flight profile with the reserve left in the S-IVB and with the total delta-V of the SM
used to boost the entire Apollo stack (CM/SM/LM). Probably add about 3500mph to that if you used both stages of the LEM as boosters and then discarded them before lighting up the SM
the first time.