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ufonut6009
2006-Feb-17, 10:17 AM
I have learned that after the explosion aboard Apollo 13, the LM fuel / thrusters were used to bring back the crew home.

I also learned (it may or may not be accurate) that LM thrusters were fired twice for the sling shot process around moon and once for re-enrty in to the earth's atmosphere.

Can someone tell me the exact number of time LM thrusters were fired and for what reason? At any point in the rescue mission did NASA tried or successfully used the fuel in CM.

Thanks.

Obviousman
2006-Feb-17, 10:34 AM
Firstly, could you provide links to your references, or details if they are books etc?

The other questions I will answer in due course (though others will no doubt beat me to it).

gwiz
2006-Feb-17, 10:35 AM
As in your other thread, try Apollo by the Numbers, all the Apollo numerics anyone could want. The LM descent engine was used for two main manoeuvres - to regain an earth return trajectory and to speed the return - and one course correction, the LM RCS for one course correction, the SM propulsion systems weren't used after the explosion. The CM propulsion was only used for attitude control during re-entry.

kucharek
2006-Feb-17, 10:55 AM
The SM RCS system was used to regain correct attitude after the explosion. The SM RCS is completely independent (own tanks) from the main propulsion system. The LM RCS tanks had cross-feeds to the main tanks of the LM.

Harald

PS: Reference to Apollo by the Numbers: http://history.nasa.gov/SP-4029/contents.htm

Glom
2006-Feb-17, 02:32 PM
Midcourse correction 1 wasn't done because the trajectory was good.

Midcourse correction 2 was done as planned with the SPS to put the spacecraft on the non-free-return trajectory.

Midcourse correction 3 wasn't done because the trajectory was good.

Then the O2 tank blew up.

Midcourse correction 4 was done with the LM DPS to put the spacecraft back on a free return trajectory.

They flew through pericynthion.

A burn at two hours after pericynthion (PC+2) was done to reduce the time of flight back.

Midcourse correction 5 was done with the LM DPS (the seat of the pants burn) to correct for drift due to the leaking sublimator.

Midcourse correction 6 wasn't done because the trajectory was good enough.

Midcourse correction 7 was done with the LM RCS for a small correction of trajectory.

kucharek
2006-Feb-17, 03:26 PM
Midcourse correction 5 was done with the LM DPS (the seat of the pants burn) to correct for drift due to the leaking sublimator.

Nitpick: The sublimator wasn't leaking. It was just,er,sublimating :-) It did what it was designed for.For trajectory calculations,it was just forgotten to put the small,but constant thrust into account it produces.Under normal circumstances,it hadn't the opportunity to work so long in flight.

MID1
2006-Feb-19, 04:46 PM
I have learned that after the explosion aboard Apollo 13, the LM fuel / thrusters were used to bring back the crew home.

I also learned (it may or may not be accurate) that LM thrusters were fired twice for the sling shot process around moon and once for re-enrty in to the earth's atmosphere.

Can someone tell me the exact number of time LM thrusters were fired and for what reason? At any point in the rescue mission did NASA tried or successfully used the fuel in CM.

Thanks.


I think I've seen this question before. I can't place it exactly, however.
You've received some good answers here pertaining to what engines were used for what on AS-13, but one thing I'd like to address for you is the statement regarding the use of LM thrusters for re-entry into the Earth's atmosphere.

No thrusters were fired "to re-enter the Earth's atmosphere" on any Apollo lunar mission's return. The trans-Earth trajectory of Apollo missions was calculated and adjusted to allow the CM to enter a narrow corridor at a precise angle at a precise place and time. Thrusters were utilized in mid-course corrections to "tweak" this trajectory, but no thrusters were necessary to enter the atmosphere. Apollo CMs were going to enter, period. I'm not sure, but I think perhaps there may be some confusion between a de-orbit burn, such as would be necessary with an orbiting vehicle, with the trans-earth trajectory of a returning Apollo CM, the latter requiring no de-orbit burn, as it was designed to simply fly into the atmosphere.

The LM thrusters at any rate, could never have been used during an Apollo re-entry, as that would imply having the LM attached to the CM during re-entry. That would've produced a very bad day for all concerned, me thinks!

There were no CM RCS thrusters used during Apollo 13's return flight...until they powered up the CM just prior to re-entry. Those thrusters were used, as in all Apollo re-entries, to stabilize spacecraft attitude and make adjustments to the lift-vector during the re-entry flight.

The LM DPS and RCS were used during the return to Earth, and the CM RCS was used during re-entry.

Phoenix Feet
2006-Feb-21, 07:48 AM
They flew through pericynthion.

What is pericynthion?


Midcourse correction 6 wasn't done because the trajectory was good enough.

I remember it being referred to as "close enough" in the movie as well. How much margin for error did they have?

Kelfazin
2006-Feb-21, 11:07 PM
Apocynthion and pericynthion are the high and low points, respectively, of an object in orbit around the moon

MID1
2006-Feb-22, 01:21 AM
What is pericynthion?



I remember it being referred to as "close enough" in the movie as well. How much margin for error did they have?

Think of pericynthion as the closest approach to the moon. Apollo 13's pericynthion occurred as they swung around behind the moon.


There really wasn't much margin for error on the MCCs that adjusted the entry corridor approach. There was a corridor of sorts that the spacecraft had to encounter the earth through. The upper boundary of this was the skip-off point, where, if you were above it, you would skip off of the earth's atmosphere, or miss it entirely and head off into a fatal orbit, and the lower boundary was the burn up point, where if you entered below it you would be toasted.

The entry angle range was somewhere between 5.5 and 7.5 degrees to the earth's horizon. The final midcourse correction of Apollo 13 set their entry angle at 6.49 degrees, which was indeed "close enough". They were basically heading right down the middle of the corridor, and executed the most precise landing in the Apollo program, and I believe in the history of manned spaceflight in the era of parachute recovery.

This was indeed remarkable, as they had to use a technique utilizing the earth's terminator and the sun to determine their spacecraft's attitude in the absence of a powered up guidance platform. This technique was researched on Apollo 8, which Jim Lovell had flown on a couple years before. This, and the fact that the burn was a three man operation, one timing the burn, one controlling roll and engine firing, and one controlling pitch rate, made Apollo 13's performace absolutely remarkable.

They called it a failure. I never considered it that at all.

Phoenix Feet
2006-Feb-22, 08:23 AM
Thanks, that's very interesting. Does that mean the worry over 13's "shallowing" in the film was made up?

gwiz
2006-Feb-22, 09:25 AM
No that was the effect of the sublimator thrust that they had to correct.

ToSeek
2006-Feb-22, 05:54 PM
They were basically heading right down the middle of the corridor, and executed the most precise landing in the Apollo program, and I believe in the history of manned spaceflight in the era of parachute recovery.

That's not correct, though I've seen it claimed elsewhere. According to Apollo by the Numbers (http://history.nasa.gov/SP-4029/Apollo_18-40_Entry_Splashdown_and_Recovery.htm), Apollo 14 was only 0.6 nautical miles off target, while Apollo 13 was 1.0 nm off - a very good result, but not the best.

NEOWatcher
2006-Feb-22, 06:15 PM
That's not correct, though I've seen it claimed elsewhere. According to Apollo by the Numbers (http://history.nasa.gov/SP-4029/Apollo_18-40_Entry_Splashdown_and_Recovery.htm), Apollo 14 was only 0.6 nautical miles off target, while Apollo 13 was 1.0 nm off - a very good result, but not the best.
1.0 Nanometers? oops, never mind.

MID1
2006-Feb-23, 11:51 PM
Thanks, that's very interesting. Does that mean the worry over 13's "shallowing" in the film was made up?


I think many things in the film were "made up", as it were...a little artistic liscence which is typically Hollywood, but not necessarily accurate. I think the "worry" was overblown, and I really don't think there was all that much worry over that aspect in reality (although I will also add that there was a general sense of worry, albeit buried under the surface, about everything froim about 55 hours GET). Trajectory held pretty well through the mid-course corrections. After the final MCC, PTC was disturbed by venting, probably via the LM sublimator and some hydrogen from the SM. This, however, did not do much but change the rates of the PTC mode.

Ron Howard told the NASA advisors to his film that he wanted to accurately portray the events, but that on occassion, Hollywood would prevail in order to keep it audience-interesting. He did that in many places in that film (quite frankly the launch sequence portrayal of the inside of the CM had me laughing, all that blurring and screaming by the crew was a wee bit over the top :razz: ), and basically told the NASA folks that when he did that, stay out of the way.

But all in all, it was basically an accurate portrayal of the technical events...albeit melodramatic in many places where it really wasn't needed (and where it really wasn't in actuality).

I thought Apollo 13 was compelling enough in its actuality without any Hollywood embellishments.

MID1
2006-Feb-23, 11:55 PM
That's not correct, though I've seen it claimed elsewhere. According to Apollo by the Numbers (http://history.nasa.gov/SP-4029/Apollo_18-40_Entry_Splashdown_and_Recovery.htm), Apollo 14 was only 0.6 nautical miles off target, while Apollo 13 was 1.0 nm off - a very good result, but not the best.


Maybe. I don't have the precise numbers. I was always more interested in having three warm bodies egress rather than how close they got to targeted points...I know 14 was within a mile of its pre-launch predicted landing point, and that 13 was in that range as well. I'd count 13 as pretty astounding performance, given the way in which they had to gain attitude information and execute maneuvers!