What if Apollo 13 Occured in an Apollo Direct Ascent Spacecraft?

[fredinno]

What would happen if an Apollo 13-esque scenario occurred on route to the moon if the NASA had chosen the "Direct Ascent" method for a lunar landing?

https://en.wikipedia.org/wiki/Direct_ascent

Since there was no "lifeboat LEM", would the astronauts inside the CM be screwed? Or would they be able to return more quickly due to having another engine capable of a direct abort? (rather than using a free-return tragectory)

[K^2]

I have no idea if it'd actually be possible given all the hardware involved, but it would have enough dV to "turn around" and return to Earth within a few hours.

[HoloYolo]

1. They die on the way home due to food and oxygen shortages.

2. They get home within a day due to the engines.

[SemiaCloud]

They would probably be screwed.

[G'th]

Funnily enough, they'd probably get home more comfortably than the real 13 did unless the entire craft went to hell. Both stages of the Direct Ascent configuration would have been able to return the astronauts home regardless of the status of the other.

Though, if the upper stage failed, they'd probably lose LS as its unlikely for the lower stage to have any of that capability when its going to just be left on the Moon.

[Frybert]

Well, considering that the SM was designed before LOR was chosen, I would assume nothing good. However, one might argue that since the LM was designed with the 'life boat' contingency in mind, some of that redundancy might have made its way into the SM just as the redesigned SMs did after A13.

[Armchair Rocket Scientist]

What would happen if an Apollo 13-esque scenario occurred on route to the moon if the NASA had chosen the "Direct Ascent" method for a lunar landing?

https://en.wikipedia.org/wiki/Direct_ascent

Since there was no "lifeboat LEM", would the astronauts inside the CM be screwed? Or would they be able to return more quickly due to having another engine capable of a direct abort? (rather than using a free-return tragectory)

They'd probably be screwed (IIRC it was deemed that trying to fire the SPS on Apollo 13 was too risky since the engine might have been damaged).

But the astronauts would also be screwed if an Apollo 13 type accident happened while the LM was on the moon, or if a severe failure happened to the LM while it was on the moon, or if an Apollo 13 type accident happened while in lunar orbit and disabled the SPS (LM on its own couldn't put the whole stack on a return trajectory AFAIK.

Ultimately, having redundant systems on the same spacecraft is safer than having multiple spacecraft where some systems are redundant but there are also plenty where a failure on EITHER spacecraft will kill the crew.

[tater]

The direct ascent ideas I have seen that NASA was looking at were 2 stage. As a result, it sort of depends where the accident occurs.

In this design:

If it occurs in the lower stage, it seems like they separate the stages, and head home. If it happens in the upper, service module, they are dead I think.

[imaspacestation]

If it occurs in the lower stage, it seems like they separate the stages, and head home. If it happens in the upper, service module, they are dead I think.

Why would they not be able to use the lower stage to burn back home?

[KerikBalm]

They'd probably be screwed (IIRC it was deemed that trying to fire the SPS on Apollo 13 was too risky since the engine might have been damaged).

I seem to recall that not all the LO2 tanks were destroyed in the blast, they could have tried using the SM engine... but they didn't want to risk it.

I assume a similar thing may have made them reluctant to use the lower stage if there had been an explosion in the upper one.

In the case of apollo 13, they had the LEM engine, so they didn't need to.

In that case... well, they'd have nothing to lose by trying to use the lower stage for an abort.

[Frybert]

The components that caused the accident were all contained in the service module, which would have been the upper stage of a direct ascent mission. It wouldn't matter if they could still have used the other stage to burn, they wouldn't have had enough power/water/oxygen to make it.

- - - Updated - - -

I seem to recall that not all the LO2 tanks were destroyed in the blast, they could have tried using the SM engine... but they didn't want to risk it.

I assume a similar thing may have made them reluctant to use the lower stage if there had been an explosion in the upper one.

In the case of apollo 13, they had the LEM engine, so they didn't need to.

In that case... well, they'd have nothing to lose by trying to use the lower stage for an abort.

One tank was destroyed and either the second tank, or plumbing near it was damaged and it leaked out shortly after the explosion. The SPS did not use oxygen however so as far as a burn goes, that wouldn't have mattered.

[KerikBalm]

Well, if the explosion vented enough to reduce the "dry mass" that the lower stage had to push, then they may have been able to do an abort that got them back sooner, before power ran out, no?

[Frybert]

The explosion happened 3 days into the mission. The fuel cell stayed on for about an hour or so until the oxygen that powered it ran out. The reentry batteries in the CM only lasted 3 hours. There would have been no burn to get them back soon enough.

[Brotoro]

I think Frybert is correct.

[fredinno]

I think Frybert is correct.

So, they're pretty much screwed, no matter what?

[tater]

Why would they not be able to use the lower stage to burn back home?

Frybert already essentially answered this question, but they'd have all the issues they had regarding life support had the malfunction still occurred in the SM (hence my initial statement that a SM explosion likely results in death). That's aside from the fact that the explosion could easily wreck any control linkages to the lower stage.

[Frybert]

So, they're pretty much screwed, no matter what?

They were extremely lucky it happened right when it did. More than a few hours earlier, they wouldn't have had enough power/water to make it back, any later and it would have been harder to get back to free return.

[Frybert]

To directly answer that, Yes. The LM was what saved them. Had they not had the LM (or some other type of redundancy system) they would have been dead within a few hours of the explosion. The fuel cells were powered by the hydrogen and oxygen tanks in the service module. Once that oxygen ran out they would have had none left to breath, and only 3 hours worth of electricity to do anything else with.