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#1
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If a lunar landing was aborted...
would the entire LM return to the CM, or would it split and only
return the ascent stage? |
#2
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If a lunar landing was aborted...
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. |
#3
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If a lunar landing was aborted...
"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. |
#4
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If a lunar landing was aborted...
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 |
#5
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If a lunar landing was aborted...
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? |
#6
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If a lunar landing was aborted...
"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. |
#7
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If a lunar landing was aborted...
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. | |
#8
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If a lunar landing was aborted...
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. | |
#9
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If a lunar landing was aborted...
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. |
#10
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If a lunar landing was aborted...
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 |
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