Apollo 10 contingency plans

[Obviousman]

A discussion came up elsewhere about the Apollo 10 practice landing; what would have happened if for some reason they were forced to actually land on the surface; could they rendezvous with the CSM again?

I know that the ascent stage did not have the fuel to make a nominal ascent but what if the CSM dropped into a low orbit? I know this was a contingency plan for later missions and practiced in the sim but would it have been feasible for Apollo 10?

Anyone have the full Apollo 10 flight plan?

[ka9q]

What would have forced them to land?

If they had, which they could have done, there would have been no way to return. There wasn't enough propellant on the ascent stage to make any kind of lunar orbit. The CSM can't rescue you unless you do that.

[Zakalwe]

I seem to remember reading somewhere that the LM didn't have the full suite of software loaded. The landing routines weren't included, so it physically couldn't land. An abort would be an abort-to-orbit or an abort to a position where the CSM could manoeuvre to recover..

I believe that this document gives the operational LM abort and rescue plan. it's not great quality though:

https://archive.org/details/nasa_techdoc_19740072573

[Luke Pemberton]

I seem to remember reading somewhere that the LM didn't have the full suite of software loaded. The landing routines weren't included, so it physically couldn't land. An abort would be an abort-to-orbit or an abort to a position where the CSM could manoeuvre to recover..

That's what I have read too, along with the post that ka9q made. The ascent stage simply did not have the fuel to establish lunar orbit, even if the CSM could manoeuvre to its minimum orbital altitude (I think this is the correct term).

[Echnaton]

IIRC, one of the reasons for the under fueling was to compensate for the LM dry mass being overweight.  Reducing the fuel kept the wet mass on budget.  The overweight also meant that if they'd had a full fuel load, making rendezvous could not have occurred according to the plan for A11 anyway.

[Northern Lurker]

What would have forced them to land?

As earthlings we are used to aviation where aircraft has actively to do something to stay up in the air. For an an aircraft in emergency, safety is making a forced landing before the plane falls from the sky.

LM of Apollo 10 made engine burn to lower their orbit but they were still in stable orbit. Should they have had problems they had time to solve them because they weren't in danger of crashing into anything. If their problem had been unsolvable the CSM would have been able to rescue the astronauts from the LM.

Lurky

[Allan F]

IF the LM was in a stable position - as in not spinning.

[Bob B.]

IF the LM was in a stable position - as in not spinning.

If the vehicles couldn't dock, I believe the contingency was to have the astronauts transfer to the CM via EVA.

[Luther]

A discussion came up elsewhere about the Apollo 10 practice landing; what would have happened if for some reason they were forced to actually land on the surface; could they rendezvous with the CSM again?

The good news is, you're the first humans in all of history to land on another celestial body!

The bad news is ...

LM of Apollo 10 made engine burn to lower their orbit but they were still in stable orbit. Should they have had problems they had time to solve them because they weren't in danger of crashing into anything. If their problem had been unsolvable the CSM would have been able to rescue the astronauts from the LM.

Just for me to confirm my understanding - so they were in a reasonably stable orbit (roughly circular?), attached to the CSM.  Then they fire up the engine to make their orbit elliptical (or more elliptical), with the low point being much much closer to the surface.  So for Apollo 10, I guess they just do nothing, riding down and then back up again, perhaps enjoying the view if they're not too busy.  But in an actual landing scenario, they wait until they're at the low point of the orbit, then fire up the engines again to put themselves down on the surface.

So the main failure scenario for Apollo 10 would then be, something goes wrong with the engine, and they're unable to return to the orbit of the CSM, in which case the CSM would have to match their orbit to pick them up.

Is that at least approximately correct?

[Allan F]

Very accurate.

[Allan F]

I don't know if the descent stage on Apollo 10 was fuelled fully - and actually had the fuel needed to soft-land.

[Zakalwe]

I don't know if the descent stage on Apollo 10 was fuelled fully - and actually had the fuel needed to soft-land.

According to Apollo By The Numbers, the A 10  descent stage had 18,218lbm of fuel, which is pretty much the same as the other descent stages.

The ascent stage was fuelled with 2,631lbm, which was 51% of the average of the other missions.

[Obviousman]

Being a hypothetical, I'm starting from the point that the LM did manage to land on the surface (I didn't know the landing routines weren't loaded).

However by what people say, the 51% propellant load would have been insufficient to get it anywhere near an altitude where an emergency rendezvous with the CSM could take place?

Is this a guess or based on some known parameters?

Anyone got Orbiter or something that can run the numbers?

[Bob B.]

However by what people say, the 51% propellant load would have been insufficient to get it anywhere near an altitude where an emergency rendezvous with the CSM could take place?

Is this a guess or based on some known parameters?

Anyone got Orbiter or something that can run the numbers?

The Apollo 10 ascent stage after staging had a mass of 8,273 lbm.  With only 2,631 lbm of propellant, and assuming a specific impulse of 311 s, then it had a Δv of only 1,167 m/s.  This is well below that needed to attain orbit.  About 1,850 m/s Δv was needed to reach orbit.

[Echnaton]

What I am seeing, that in the case of a hypothetical landing, say Stafford and Cernan had made a long shot bid at history there was one shot for a rescue.  It would have been to shoot up in and acr that crossed the with the CSM's orbit. And hope the CSM could snag them during the brief time while the arc and orbit crossed.  Probably by abandoning the LM and jumping into space with one chance to catch the CSM.  If that didn't work the Young would have a few minutes to maneuver to them before the arc took them too far away.

That's the movie version anyway.  I suspect the velocity differences would have made it impossible even if the craft crossed close enough.  Bob would a Δv of 1,167 m/s been sufficient to make it to the minimum altitude for a CSM orbit?