posted 08-05-2010 10:08 AM               

Bearing in mind the weight constraints when launching the Apollo stack, i.e. payload versus fuel required, what limits were placed on the lunar crews as to how much they could gather for return to Earth? If there were limits, how did the crews weigh their samples and what degree of latitude did they have?

posted 08-05-2010 12:08 PM               

[Comm Break. The crew has a small spring scale which gives them terrestrial weights. That is, on Earth, a two-pound (Earth-weight) rock would register twelve pounds on the scale while, on the Moon, it would register two pounds. The actual weight of rocks collected during this EVA is given in the Mission Report as 31 pounds (14 kg). The 48-pound (21.8 kg) total given here includes the weights of the individual sample bags, the two 1.7 pound (0.8 kg) SCBs, and the 14.7 pound (6.7 kg) SRC. Weights are measured so that the flight engineers can adjust the stowage for center-of-mass control, if necessary.]

This also would determine how much gear (Backpacks, Overshoes, Food Bags,etc) would be jettisoned prior to launch.

posted 08-06-2010 02:36 AM               

• 11 - 19.9kgs;
  
• 12 - 34kgs;
  
• 14 - 44.5kgs;
  
• 15 - 78.5kgs;
  
• 16 - 95.4kgs;
  
• 17 - 114.8kgs.

posted 08-06-2010 02:40 PM               

quote:

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Originally posted by kr4mula:
Keep in mind that from 15 on, they were leaving behind the lunar rover as part of the jettisoned equipment. I don't know its weight, but I'm sure it exceeded the masses of the rocks you cited.

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The argument is getting a little far afield. The Descent Engine bore the weight of the Rover, and the Rover was never intended to be lifted by the Ascent Stage.

What was interesting to me about the Ascent Engine was that it was not powerful enough on its own to take the Ascent Stage into orbit. The RCS thrusters also fired during lunar liftoff to give the LM enough of a boost to achieve orbit.

Does anyone have statistics on exactly how much "wiggle room" there was in the Ascent Stage mass related to the available thrust to get to lunar orbit rendezvous? I know that fuel was precious, but I assume that storage space was also an issue (e.g., where would you store 2 PLSS's in the CM on the way home, and why would you bother, if you didn't need them?).

posted 08-06-2010 03:30 PM               

quote:

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Originally posted by moorouge:
1975 figures from NASA give the returned sample weights as

11 - 19.9kgs;

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After a lot of searching, I found that the Apollo 11 maximum sample allocation was 50 lbs, or about 23 kg. I would assume then that the weights are Earth weights.

posted 08-06-2010 04:32 PM               

quote:

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Originally posted by ilbasso:
What was interesting to me about the Ascent Engine was that it was not powerful enough on its own to take the Ascent Stage into orbit. The RCS thrusters also fired during lunar liftoff to give the LM enough of a boost to achieve orbit.

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posted 08-07-2010 01:25 PM               

Page 292 of "How Apollo Flew to the Moon" states that the RCS thrust was about 1/10 that of the Ascent Engine, and that the RCS could have been used to supplement the Ascent Engine if it was under-performing.

posted 08-08-2010 06:41 AM               

quote:

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Originally posted by SpaceAholic:
the Ascent engine had a rated ISP of 15.5 KNewtons (3500 pounds in a vacuum) more then sufficient to independently address ascent impulse requirements.

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posted 08-08-2010 10:36 AM               

Hopefully, this will give you an idea of how the "rock boxes" were distributed in the Ascent Stage as well as the weight of the rocks carried up from the lunar surface.

I know from talking to Dick Gordon that he needed the weights of the "rock boxes" so he could establish the proper CG for reentry.

posted 08-08-2010 01:44 PM               

quote:

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Originally posted by SpaceAholic:
Rather then providing the answer(s) outright, I suggest reviewing SP-4029.

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posted 08-08-2010 05:10 PM               

quote:

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Originally posted by SpaceAholic:
Pop quiz: Which lunar landed LM Ascent stage possessed the heaviest dry weight?

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The heaviest fueled LM was Apollo 17 at 10,997 lbs (5634 lbs less fuel).

posted 08-09-2010 08:17 AM            

Y = Allowable weight of LM ascent stage at lunar lift off dependent on ascent stage engine thrust

Z = The amount of safety margin or in other words the difference between the possible weight that can be carried into lunar orbit and the allowed weight to be carried back into lunar orbit decided upon by NASA

So X = Y - Z

A more precise calculation would have been worked out as illustrated by what Gene Cernan wrote in his book, "The Last Man On The Moon."

Back inside, we did some last-minute cleaning and tossed a bunch of very expensive gear out of the spacecraft. Cameras, tools, backpacks and other now useless material were flung to the surface. We had to shed weight if we were going to get off the moon safely. Mission planners had worked out the exact balance needed, and every container of rocks we bought aboard was weighed on a handheld fish scale, calibrated for one-sixth gravity before being stored. We had just enough fuel to get us into orbit, with almost no margin for error, so the overall weight of the spacecraft, its passengers and cargo of rocks was critical. We threw out nearly everything that wasn't nailed down.

Since we were taking 250 pounds of moon rocks and soil back with us, we had to dump everything that we wouldn't need. We carried a kind of fish scale that we used to weigh everything we brought into the spacecraft.

...we weighed our rocks and soil samples. The total came to 44 pounds... we were allowed to bring back 215 pounds, so we had plenty more collecting to do.

First we weighed our rock and soil samples, because we needed an exact weight at lift-off for our computer to fine tune our ascent trajectory and burn time. After weighing everything, Houston said we had collected a total of 245 pounds during our three day stay. When more accurate measurements were taken later on the earth, it turned out there were actually 213 pounds. They had a little concern about our weight and for a while we thought we might have to jettison some of our rocks, but Houston decided to go with all we had.

posted 08-09-2010 02:23 PM               

quote:

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Originally posted by robsouth:
Why did the weight allowance increase? Maybe the added length of time on the surface just allowed for more samples to be collected. Maybe the margin of error was relaxed on later flights.

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posted 08-09-2010 03:08 PM               

I heard from Dave Scott.

In relation to the other astronauts' comments, he also said that there were limits determined prior to liftoff. If you tie his answer to the book quotes from Cernan, Duke and Irwin, there was a limitation determined prior to the mission. The Apollo 15 crew did notify Mission Control about the total rock weight and was within their weight limits.

I know of two lunar rock spring scales that returned to Earth after use on the Moon. Apollo 14's is at the Astronaut Hall of Fame and the other is in a private collection.

posted 08-10-2010 06:56 AM            

171:43:23 Duke: Houston, Orion. Over.

171:43:25 England: Go ahead, Charlie.

171:43:30 Duke: Okay. We've got some weights for you, if you're ready to copy.

171:43:33 England: All set.

171:43:37 Duke: Okay. The BSLSS rock bag, the big rocks, will weigh 40 pounds; bag 7, SCB number 7, is 33; SCB number 4 is 25; SCB number 6 is 20. I get a total out of that of about 118 (pounds). Over. (Pause)

171:44:01 England: Okay, we concur.

[Comm Break]

171:45:06 England: Okay. We're working those numbers over here.

171:49:52 England: Hey, fellows, you have 245 pounds of rocks. (Pause) That's not including the weights of the SRCs.

171:50:05 Young: Okay, has some got to go back?

171:50:09 England: No, I think we're going to be able to find a way. You got an in-plane launch, so things look pretty good. But we're working it here.

171:50:20 Slayton: (Joking) Probably have to throw that big one away, John.

171:50:39 Young: Okay. Well, we don't want to throw away any that don't need to be throwed away. That's for sure.

ALSJ [They are over the planned limit for samples and, in principle, would be cutting into propellant margins if they kept them all. As Tony mentions, however, the Command Module orbit is perfectly lined up so that John and Charlie wouldn't have to apply any lateral thrust to achieve the rendezvous. Nonetheless, the fact that Houston is taking a long time to make a decision about the over-limit samples is indicative of the pragmatic conservatism that motivated most operational decisions in Apollo.]

171:56:25 Young: Roger. We're ready to tie up the jett bag.

171:56:28 England: Okay. We're still trying to get a decision on these rocks down here, if you could hold on one.

172:05:59 England: Okay, Orion. We're go with the rocks you've got.

172:06:07 Young: Outstanding. Thank you very much.

[Cernan - "Each pound mattered. I'm not saying that we would have thrown out a pound of rock. There were margins. But, weight translated into less Delta-V(elocity) and into fuel."]

posted 08-10-2010 10:00 AM               

171:50:09 England: No, I think we're going to be able to find a way. You got an in-plane launch, so things look pretty good. But we're working it here.