If a lunar landing was aborted...

would the entire LM return to the CM, or would it split and only
return the ascent stage?

On Sat, 06 May 2006 13:31:31 GMT, PowerPost2000 wrote:

would the entire LM return to the CM, or would it split and only
return the ascent stage?

During powered descent, that is.

"PowerPost2000" wrote in message
...
On Sat, 06 May 2006 13:31:31 GMT, PowerPost2000 wrote:

would the entire LM return to the CM, or would it split and only
return the ascent stage?

During powered descent, that is.

I believe it depended on how low they were at the time. Apollo 10 obviously
showed they could split and return.

Greg D. Moore (Strider) wrote:
"PowerPost2000" wrote in message
...
On Sat, 06 May 2006 13:31:31 GMT, PowerPost2000 wrote:

would the entire LM return to the CM, or would it split and only
return the ascent stage?

During powered descent, that is.

I believe it depended on how low they were at the time. Apollo 10 obviously
showed they could split and return.

I just reviewed the LM Abort Guidance System (AGS) documentation. The
AGS was programmed to use fuel from both the descent and ascent stages
to perform a successful return and rendezvous with the CM. So, in an
abort situation, the LM AGS didn't automatically cast off the descent
stage if there was still useable fuel onboard.

http://ntrs.nasa.gov/archive/nasa/ca...1975018954.pdf

Apollo experience report guidance and control systems: Lunar module
abort guidance system
Kurten, P. M.
NASA Center for AeroSpace Information (CASI)
NASA-TN-D-7990; JSC-S-424 , 19750701; Jul 1, 1975


-Rusty

Compare to the Soviet L-3 landing profile:

1. A braking stage slows the LM/CSM stack into lunar orbit.

2. Cosmonaut boards LM (attached to braking stage), CSM casts off

3. Braking stage fires again to achieve 95% delta-V for landing,
is jettisoned a few kilometers above the surface.

4. L3 engine turns on and completes soft landing [NO abort mode if engine
failure]

5. For ascent, landing platform/legs is left behind but SAME L3 engine
fires to put L3 in lunar orbit.

6. L3 docks with CSM.

7. CSM fires its engine [first ignition in mission] for TEI.

SPORTY ain't even half of it! No graceful degradations, no abort modes
or alternate ignition opportunities. It was a death-in-space trap.




"PowerPost2000" wrote in message
...
would the entire LM return to the CM, or would it split and only
return the ascent stage?

"Jim Oberg" writes:

Compare to the Soviet L-3 landing profile:

1. A braking stage slows the LM/CSM stack into lunar orbit.

2. Cosmonaut boards LM (attached to braking stage), CSM casts off

Don't forget: no docking tunnel, transfer to/from CSM requires one man
EVA.

3. Braking stage fires again to achieve 95% delta-V for landing,
is jettisoned a few kilometers above the surface.

4. L3 engine turns on and completes soft landing [NO abort mode if engine
failure]

5. For ascent, landing platform/legs is left behind but SAME L3 engine
fires to put L3 in lunar orbit.

There was a backup engine which was not used in the nominal profile, so
there was some consideration given to failure modes, but I agree that it
was an extraordinarily risky profile. (Actually, the plan called for
both engines to be ignited simultaneously, with the backup engine to
shut down if the primary engine was OK. If on descent that was not the
case, the primary would shut down and the landing would be aborted. On
ascent from the surface, failure of the primary would cause the ascent
to be flown with the backup.

6. L3 docks with CSM.

7. CSM fires its engine [first ignition in mission] for TEI.

Again, there was a backup engine. Still, waiting until this point to
see if they work is pretty risky.

SPORTY ain't even half of it! No graceful degradations, no abort modes
or alternate ignition opportunities. It was a death-in-space trap.

Also, there was the double skip reentry to avoid a 20+G ballistic
profile, sure to cause injury (at best) to the crew after 2 weeks in
weightlessness.

In article ,
PowerPost2000 wrote:
would the entire LM return to the CM, or would it split and only
return the ascent stage?

If the abort is during the landing proper, typically only the ascent stage
would make it back to the CM. But whether the LM would stage immediately,
or use up the descent-stage fuel first as part of the ascent, would depend
on just when the abort happened and just what had gone wrong.

Remember that the planning had a very strong bias toward preserving
options whenever possible. Since staging the LM is irreversible and
precludes any further use of descent-stage resources, you want to postpone
staging as long as possible, other things being equal.

Immediate staging was the riskiest form of abort, much more drastic than
just throttling up the descent stage and heading back up, so it got more
attention, including a live test on Apollo 10. But that doesn't mean it
was preferred; quite the contrary.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

In article , Chris Jones wrote:
Also, there was the double skip reentry to avoid a 20+G ballistic
profile, sure to cause injury (at best) to the crew after 2 weeks in
weightlessness.

Not very different from Apollo there. On Apollo too, the alternative to a
lifting reentry was a really nasty pure-ballistic one.

The difference between Apollo's equilibrium-glide reentry and a skip
reentry was minor by comparison, a matter of how much range was needed to
make the preferred landing site. In fact, Apollo did originally plan to
use a skip reentry, and that plan was changed for relatively minor
secondary reasons. (Landing-site requirements were relaxed -- the first
Apollo specs had demanded land touchdown in the continental US -- and it
became clear that while the primary guidance system could fly a skip, the
backups couldn't easily do it.)
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

PowerPost2000 wrote:

would the entire LM return to the CM, or would it split and only
return the ascent stage?

Depends on at what time in the process. There is a point of no return and
you have to complete the landing, then take off again.

Jim Oberg wrote:

4. L3 engine turns on and completes soft landing [NO abort mode if engine
failure]

5. For ascent, landing platform/legs is left behind but SAME L3 engine
fires to put L3 in lunar orbit.




Remember hat there are two engines on the LK; the main center one, and
another one that has two trust chambers located one to each side of the
central nozzle, similar to the set-up used on the original Soyuz
equipment module.
On ignition for the ascent from the Moon, both motors would be ignited
simultaneously, then the twin-nozzled back-up engine would be shut down
as soon as it was certain the central motor was operating properly.
I assume the same technique was to be used in the case of a descent
abort due to the main engine having trouble; ditch the landing gear and
fire the back-up motor to ascend back into orbit.

Pat