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Post by Kiwi on Aug 21, 2009 7:50:43 GMT -4
Just a quick note to say I'm enjoying this thread too, as I'm sure others would be. It shows the difference between Comics/Science Fiction/Fantasy and reality. In the comics and movies they always have unlimited fuel, no need of Newtonian mechanics, and the spacecraft can usually soar and can be heard from a distance. In reality in the 1960s-70s, there was no noise or soaring in space, fuel was very limited, and as a result, Mr Newton had to do the driving. How he did it, is what we see here. those guys are pretty smart The more I learn about the astronauts, engineers, designers, flight controllers and back-room people, the more I can apply the word "smart" to all of them. Back then, NASA could, and did, hire the very best. On the other hand, the one word that fits so many hoax-believers and promoters is "ignorant."
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Bob B.
Bob the Excel Guru?
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Post by Bob B. on Aug 21, 2009 17:11:09 GMT -4
Just a quick note to say I'm enjoying this thread too, as I'm sure others would be. It shows the difference between Comics/Science Fiction/Fantasy and reality. In the comics and movies they always have unlimited fuel, no need of Newtonian mechanics, and the spacecraft can usually soar and can be heard from a distance. In reality in the 1960s-70s, there was no noise or soaring in space, fuel was very limited, and as a result, Mr Newton had to do the driving. How he did it, is what we see here. I really enjoy playing around with this orbital mechanics stuff, obviously. I find it really fascinating how, with nothing more than a few simply equations, one can predict the behavior of the universe. I like the challenge of trying to solve a problem and the new knowledge that is gained in the pursuit. I also find it rewarding when my solution is confirmed, or when I'm able to replicate someone else's solution. Whenever I've applied my efforts to Apollo, I've always been able to produce a very close match. That's why I get so infuriated when HBs spew some nonsense about how this or that wouldn't work, or how I just mindlessly believe what I've been told. It's very insulting. Getting back to the rendezvous problem, below is another graph that I produced from my simulation showing the separation between the CSM and LM for the LM rescue scenario. Compare this to Figure 17 on page 56. (Pretty good match.)
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vq
Earth
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Post by vq on Aug 21, 2009 21:00:15 GMT -4
The NASA method waits longer for TPI and then uses a relatively large vertical delta-v component (I used almost no vertical component). I think the NASA method is as it is because of the way the active spacecraft must sight on the target. I don't fully understand it, but surely they do what they do for a reason (those guys are pretty smart). Could it be related to contingency maneuvering? In an emergency situation where manual orientation and burns were required, maybe pointing at the CSM with the radar was more practical than pointing prograde.
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Post by homobibiens on Aug 21, 2009 23:13:25 GMT -4
Just a quick note to say I'm enjoying this thread too, as I'm sure others would be. At least one other! I would love to work through the numbers of Bob B.'s scenarios myself, I just need the time and the skill. I am confident I can develop the skill, if I can find enough time; I am less confident that I can find that time
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Post by Kiwi on Aug 22, 2009 6:45:27 GMT -4
Mr Newton had to do the driving. Damnit, I couldn't remember the exact quote by Mike Collins when I wrote that, and couldn't find it in his excellent book, Carrying the Fire: An Astronaut's Journeys, which I've been kindly loaned by fellow-member Ajv. Anyway, here is the full story, already typed up in my "Interesting bits in Apollo books" file:
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Bob B.
Bob the Excel Guru?
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Post by Bob B. on Aug 22, 2009 13:10:36 GMT -4
I would love to work through the numbers of Bob B.'s scenarios myself, I just need the time and the skill. I am confident I can develop the skill, if I can find enough time; I am less confident that I can find that time It's not all that hard once you get the hang of it. Most of what I do is really pretty basic stuff. The key, I think, is gaining a mastery of those basics and having a good problem solving mind. If you can master all the lessons in my web page, you'll have a good foundation to build on. From there it's just a matter of figuring out how to creatively apply those lessons. Each new problem solved expands your knowledge base and allows you to take on new and more challenging problems. I also find that reading the NASA missions reports and other documents gives a a great deal of insight into how things are done. It is fun when you have a knowledge of both the science and the procedures.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Aug 22, 2009 13:11:51 GMT -4
I like that quote; thanks for posting it.
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Post by ka9q on Aug 24, 2009 1:19:57 GMT -4
I am traveling and do not have my copy of "Carrying the Fire" but I am pretty sure Collins said that as long as the lunar module could make some kind of orbit (and in the right plane, I would add) then he was prepared to go down and rescue them if necessary. He had a big book of something like a dozen or more rendezvous scenarios that were a very large part of his training as a CMP, and he was more than a little relieved when Eagle made it back into a nominal orbit.
All this is consistent with what we've seen here: the LM ascent stage absolutely must have enough fuel to reach orbit, but as long as it can, CSM rescue is entirely feasible.
I add parenthetically that while Snoopy did not have enough ascent fuel to reach orbit, that fuel was sufficient to propel it out of lunar orbit to lunar escape velocity. It remains as the only flown Apollo LM ascent stage that's still intact, out there circling the sun forever unless someday we find it and bring it back to the Smithsonian...
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Post by ka9q on Aug 24, 2009 1:38:36 GMT -4
According to the book Lost Moon (now retitled Apollo 13) by Jim Lovell and Jeffrey Kluger, astronauts didn't have suicide pills but there were persistent rumours that they did. Correct. And then he said just what I would have said: what's the point in suicide pills when you can just reach over and open the cabin dump valve?
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Post by ka9q on Aug 24, 2009 1:44:46 GMT -4
I think somebody asked about the violence of the LM's crash onto the moon. It was pretty violent. The de-orbit maneuver was directly analogous to a re-entry burn from earth orbit. Only when you enter the atmosphere in a CM, a heat shield lets the atmosphere slow you down safely to the point where you can deploy parachutes and get rid of the remaining energy. No such possibility exists on the moon, so the ascent stage hits with nearly orbital energy, about 0.8 tons of tnt by my calculation. According to Apollo By The Numbers, the crater was about 10 meters.
I wonder if any recognizable pieces were left. Even at that speed I suspect there might be something to indicate that this wasn't an ordinary meteorite. The impact angle was also very shallow, about 3-5 degrees or not much more than a standard airplane landing slope. I expect the craters should be elongated a little, and that might make them easier to spot in LRO imagery.
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Post by Ginnie on Aug 24, 2009 19:09:51 GMT -4
I wonder if any of the LRO images has photographed the sites of any object that has crashed on the moon?
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vq
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Post by vq on Aug 24, 2009 20:41:10 GMT -4
I think somebody asked about the violence of the LM's crash onto the moon. It was pretty violent. The de-orbit maneuver was directly analogous to a re-entry burn from earth orbit. Only when you enter the atmosphere in a CM, a heat shield lets the atmosphere slow you down safely to the point where you can deploy parachutes and get rid of the remaining energy. No such possibility exists on the moon, so the ascent stage hits with nearly orbital energy, about 0.8 tons of tnt by my calculation. According to Apollo By The Numbers, the crater was about 10 meters. I wonder if any recognizable pieces were left. Even at that speed I suspect there might be something to indicate that this wasn't an ordinary meteorite. The impact angle was also very shallow, about 3-5 degrees or not much more than a standard airplane landing slope. I expect the craters should be elongated a little, and that might make them easier to spot in LRO imagery. Just a question of background - do objects ever "bounce" when striking an airless body at an oblique angle and orbital speed? It seems like pieces of the ascent stage could be spread out over a very large area.
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Post by ka9q on Aug 25, 2009 3:04:43 GMT -4
Just a question of background - do objects ever "bounce" when striking an airless body at an oblique angle and orbital speed? It seems like pieces of the ascent stage could be spread out over a very large area. I don't know about "bouncing" but there are elliptical craters and crater chains on the moon, and pieces flying out of a primary crater can produce secondary craters.
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Post by Czero 101 on Aug 25, 2009 3:46:43 GMT -4
Just a question of background - do objects ever "bounce" when striking an airless body at an oblique angle and orbital speed? It seems like pieces of the ascent stage could be spread out over a very large area. Surveyor 3 bounced when it landed on the Moon: From Wiki - Surveyor 3Granted Surveyor 3 wasn't coming in at orbital speeds, but I don't think that really makes a difference. Airless or not, there's no reason to assume that an object wouldn't bounce, assuming of course that anything was left after the initial impact. Cz
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Post by gwiz on Aug 25, 2009 6:38:09 GMT -4
I wonder if any of the LRO images has photographed the sites of any object that has crashed on the moon? There were several such sites photographed by Apollo missions, such as the S-IVB and Ranger ones. I recall seeing the pictures in the Preliminary Science Reports.
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