[Zickzack]

> Collins was largely powerless to help if something went wrong. If that did happen, he would have been faced with the choice of abandoning his crewmates to die on the moon and fly back to Earth himself.

He would have died in orbit then, just a little bit closer to the rest of mankind. There was no was way for him to return to solid Earth unless the lunar module came back. He was dependent on the outcome of the Lunar mission and he was not even allwed to set his foot onto Moon. One of my heros since childhood...

[hbrav]

Err, this isn't correct. There would be be nothing preventing the command module from returning home in the event of the lunar lander not coming back from the moon. Though of course the command module pilot would be a bit more task-loaded.

I think you're thinking of the other way around - the LEM would have been unable to return to earth with the command and service modules. It lacked a heatshield.

[pdonis]

> There was no was way for him to return to solid Earth unless the lunar module came back.

I'm not sure what you're basing that on. The Apollo 11 flight plan, available on the NASA website [1], shows LM jettison before TEI burn. That indicates that the LM was not needed for TEI. If for some reason the LM did not come back from the surface of the Moon, the CSM could still execute the TEI burn.

[1] https://www.hq.nasa.gov/alsj/a11/a11fltpln_final_reformat.pd...

[mulmen]

The LM does return to the CSM before the burn so it is conceivable it was needed for some preparatory step before TEI. Perhaps a fuel transfer or some guidance calculations or some other maneuvers. That it was jettisoned before the burn tells us nothing about the necessity of the module up to the moment it was jettisoned.

[pdonis]

> The LM does return to the CSM before the burn so it is conceivable it was needed for some preparatory step before TEI.

The flight plan makes clear that this is not the case.

> Perhaps a fuel transfer or some guidance calculations or some other maneuvers.

Even without reading the details of the flight plan, the LM was designed to carry just enough fuel to get down to the Moon's surface and back up again, with no extra fuel for other maneuvers; there wasn't any margin for any extra if the mission was to be doable at all. So it doesn't seem plausible that the CSM would have had to depend on getting some fuel transferred back from the LM in order to execute TEI.

As far as guidance calculations, that doesn't seem plausible either. The CSM, having been in a single stable orbit the whole time, would be expected to have much better guidance information than the LM, which had just executed a series of maneuvers, some of which were under manual control.

[mulmen]

Sure, that all makes sense, and we know how it worked and that the LM was not needed. I’m just saying that we can’t infer the LM was unneeded for TEI just because it was jettisoned.

[pwg]

Hmm, wouldn't the simplest explanation for the LM returning to the CSM before the TEI burn be for the simple reason of returning the two crew-members who went to the lunar surface to the CSM before initiation of the TEI burn?

[mulmen]

Yeah, of course, but that doesn’t mean that was the only reason, and since that had to happen maybe TEI relied on the return of the astronauts and/or LM from the Lunar surface.

My point was just that if our only information is that the LM returned to the CSM and was jettisoned before TEI we can’t deduce that the LM was not needed for TEI.

[pwg]

If that was the only information, then yes, we can't deduce whether it was, or was not, needed.

But there is other information available:

https://lithub.com/what-if-we-got-stuck-on-the-moon/

Command module pilot Mike Collins, who could only keep orbiting in the mothership while his comrades waited out the countdown to lunar liftoff, worried enough for all three of them. “I have been flying for 17 years, by myself and with others,” he would write in his post-mission memoir. “But I have never sweated out a flight like I am sweating out the LEM [liftoff] now. My secret terror for the last six months has been leaving them on the moon and returning to Earth alone; now I am within minutes of finding out the truth of the matter. If they fail to rise from the surface, or if they crash back into it, I am not going to commit suicide; I am coming home, forthwith, but I will be a marked man for life, and I know it. Almost better not to have the option I enjoy.”

Two key sentence fragements: "leaving them on the moon and returning to Earth alone" and "If they fail to rise from the surface, or if they crash back into it, I am not going to commit suicide; I am coming home, forthwith". Both indicate that Collins fully believed he could execute TEI should the LM fail to return. The only way he could possibly "return[ing] to earth alone" should the LM "fail to rise from the surface" would be if the CSM could execute TEI without the LM ever returning from the lunar surface.

Which would indicate that the LM was not required in any way for TEI.

[jhgb]

The fact that Apollo 8 CSM flew to lunar orbit and back to Earth without any LM involvement easily defeats all your arguments.

[Latty]

A necessary fuel transfer, at least, wouldn't make sense. If fuel was needed to come back, sending it down and back again would have just meant wasting more fuel for no benefit to lug it there and back again.

[mulmen]

Wait really? I never knew that. I thought the CSM had guidance and the main engine, why did he need the LEM to get home?

[trothamel]

That's correct. He could have gotten home without the LM. (See Apollo 8, which didn't have an LM at all.)

[jhgb]

> There was no was way for him to return to solid Earth unless the lunar module came back.

Where did you get that idea from? This is the first time I see someone claiming something like that.

[iqr11]

Probably from the film Apollo 13, which depicts (likely wise) hesitance to fire the SPS due to suspected damage and instead firing midcourse correction burns with the LEM descent stage while attached to the CSM. By contrast, during the otherwise normal Apollo 11, SPS was responsible for returning Collins and the CSM to Earth (TEI) whether he retrieved Armstrong and Aldrin or not. The latter case was a rehearsed abort and the stakes were known, but the maneuver was otherwise the same as a normal TEI (excluding LEM jettison, obviously). Nixon’s backup speech illustrates this, as it eulogizes those two alone; Collins would have most likely returned on his own in that horrible circumstance barring a further failure of some kind.

[GekkePrutser]

> instead firing midcourse correction burns with the LEM descent stage while attached to the CSM.

The descent stage was left on the moon so that would have been the LM ascent stage. They had 2 separate motors for descent and ascent.

But indeed Apollo 13 was very different. I think on normal missions they only brought the LM back along for TEI so as not to litter the surface with crashed LMs.

[205guy]

Why make (wrong) guesses when you can find the answer in minutes on Wikipedia? Plus it doesn’t make sense to do a TEI with unnecessary mass. From https://en.wikipedia.org/wiki/Apollo_Lunar_Module :

“The six landed descent stages remain at their landing sites; their corresponding ascent stages crashed into the Moon following use. One ascent stage (Apollo 10's Snoopy) was discarded in a heliocentric orbit after its descent stage was discarded in lunar orbit.“

Elsewhere, I read that the ascent stages were crashed into the moon to provide impulses for the seismometers left on the moon. Snoopy is still in orbit around the sun. And the one from Apollo 13 is in the Tonga Trench. Two fascinating lists:

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

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

As for littering the surface of the moon, I was surprised to see in videos that in addition to the scientific equipment ( and golf balls) they left on the moon, there was a lot of other little pieces. In one of the videos on the rover, they literally remove the cover off something and just throw it aside on the ground.

[GekkePrutser]

I was on my phone (materialistic app) so even a wikipedia search is difficult :) I hate using the web on a mobile, it feels like I'm looking through a toilet roll.

But I mentioned it was an assumption... The parent poster mentioned that the ascent stage was carried into TEI so I assumed that was true.

[kyberias]

That is not true. They jettisoned the Eagle's ascent stage and returned with Columbia.