Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Feb 15, 2010 21:19:26 GMT -4
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Post by brotherofthemoon on Feb 15, 2010 21:22:01 GMT -4
I'm not gonna pretend to be a rocket scientist, but look at this way:
The LM DPS was generating 3,000 pounds of thrust on landing. The area of the DPS nozzle extension at it's exit is around 2,300 square inches. So, the nozzle pressure would be about 1.3 PSI. This is about the same amount of pressure applied to the ground by someone weighing around 200 pounds. Factor in the fact that the engine shut down six feet about the lunar surface, and was operating in a vacuum, and the surface isn't going to be disturbed a whole lot. Actually, I'm surprised by how much it's disturbed in some photographs.
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Post by Kiwi on Feb 16, 2010 6:48:19 GMT -4
Porphyry: You have repeatedly been referred to the Apollo Lunar Surface Journal by members here, yet I don't recall a single acknowledgement from you about what a spectacular resource it is. Have you read each journal to see what the crews said about dust as they came in to land? Watched the 16mm films of the landings to see the dust being fired outward and obscuring the surface? As usual, hoax-believers show they know very little about Apollo. Besides the links already posted here, there are also the distant shots of the Apollo 15 and 17 LMs, both showing light areas around and behind them. I include the ALSJ's captions -- Apollo 15AS15-84-11324 www.hq.nasa.gov/office/pao/History/alsj/a15/AS15-84-11324HR.jpg144:50:48 Twenty years after the mission, this 500-mm photo was still Dave's favorite. It shows the LM as seen from Station 6, with Pluton Crater in the background. The ALSEP site is about one-fiducial separation to the left of the LM.Pan Camera 9814 www.hq.nasa.gov/office/pao/History/alsj/a15/a15.pan9814.jpgThis frame was taken during the CSM Rev. 50 pass over the landing site, two revs after LM liftoff and shortly after 9809 was taken. The LM can be seen near the center of a detail.www.hq.nasa.gov/office/pao/History/alsj/a15/a15.pan9814LM.jpgThe landing site is in the light patch with two lighter areas above the nose shape of Hadley Rille. Look at landing site maps in the ALSJ's Apollo 15 Image Library to get an idea of scale in this photo. The largest boulders in the bottom of the rille are probably as big as houses. Note the clash in the above caption: "two revs after LM liftoff" and "The LM can be seen..." I've emailed Eric Jones about it. Apollo 17AS17-139-21204 www.hq.nasa.gov/office/pao/History/alsj/a17/AS17-139-21204HR.jpgJack Schmitt took this superb picture of the LM from Station 6 with the 500-mm lens. Note the lighter surface around the spacecraft, produced by the sweeping action of the descent plume. Station 6 is about 3.1 kilometer from the LM, which is about 7 meters tall. The two large craters beyond the LM with prominent rim boulder fields are probably Hess (left) and Mackin (right), which are both about 6 km from Station 6 on higher ground than the landing site. Each of the craters is about 600 meters in diameter.AS17-140-21493 www.hq.nasa.gov/office/pao/History/alsj/a17/AS17-140-21493HR.jpg165:34:03 This frame is part of the Station 6 pan that Gene took from a position upslope of Tracy's Rock. The LM can be seen beyond the boulder, in a line with the point where the eastern slope of the South Massif meets the valley floor. Henry Crater, is the large feature at the base of the North Massif beyond Tracy's Rock and is about 500 meters in diameter. Locke Crater in on the northwest rim of Henry, above the back of the Rover. Note the traverse gravimeter that Gene placed on the surface shortly after he and Jack arrived at Station 6. See, also, a labeled detail.www.hq.nasa.gov/office/pao/History/alsj/a17/a17lbl21493.jpg
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vq
Earth
What time is it again?
Posts: 129
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Post by vq on Feb 17, 2010 0:46:32 GMT -4
Was the durability/cohesion of the regolith a surprise to A11? I know some of the missions had a bit of difficulty gathering core samples.
For example, would a selenologist have predicted a day before the landing that the crater would have been bigger?
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Post by Kiwi on Feb 17, 2010 3:48:56 GMT -4
Yes. Getting the flag staff into the regolith was the first problem and proved much more difficult than anyone thought.
From the ALSJ at the end of "One Small Step":
[Armstrong (Post mission press conference) - "We had some difficulty, at first, getting the pole of the flag to remain in the surface. In penetrating the surface, we found that most objects would go down about 5, maybe 6, inches and then it would meet with a gradual resistance. At the same time, there was not much of a support force on either side, so we had to lean the flag back slightly in order for it to maintain this position."]
[Later crews hammered the staff into the ground.]
[Armstrong, from the 1969 Technical Debrief - "The flagstaff was pushed into the ground at a slight angle such that the c.g. (center of gravity) of the overall unit would tend to be somewhat above the point at which the flagstaff was inserted in the lunar surface. (That is, they tilted the flag so that it would balance.) That seemed to hold alright, but I noted later, after getting back into the LM, that the weight of the flag had rotated the entire unit about the flagpole axis such that the flag was no longer pointed in the same direction as it was originally. I suspect that the weight of the flagpole probably had shifted its position in the sand a little bit from the position where it had originally been installed."]
[Aldrin, from the 1969 Technical Debrief - "How far would you estimate you got it into the ground?"]
[Armstrong, from the 1969 Technical Debrief - "Six to eight inches was about as far as I could get it in."]
[Aldrin, from the 1969 Technical Debrief - "It was fairly easy to get it down the first 4 or 5 inches."]
[Armstrong, from the 1969 Technical Debrief - "It gets hard quickly."]
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Post by ka9q on Feb 17, 2010 5:31:20 GMT -4
What's the clash? The LM descent stage was still there after ascent. You can still see it there today in the LRO images.
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Post by JayUtah on Feb 17, 2010 16:07:17 GMT -4
For example, would a selenologist have predicted a day before the landing that the crater would have been bigger?Geologist Tom Gold maintained right up until July 1969 that the lunar surface would be too fine and loose to support the LM and the astronauts, even though there was ample photographic evidence from the Surveyor program that the lunar regolith was compact and reasonably rigid. Naturally he therefore believed the engine would dig a huge crater that would engulf the craft entirely. Fortunately Gold was in the minority, but it did come as a relative surprise just how quickly the lunar regolith compacted at depths lower than 10 cm or so. We know now why this is, but it was a surprise indeed.
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vq
Earth
What time is it again?
Posts: 129
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Post by vq on Feb 18, 2010 2:59:53 GMT -4
Geologist Tom Gold maintained right up until July 1969 that the lunar surface would be too fine and loose to support the LM and the astronauts, even though there was ample photographic evidence from the Surveyor program that the lunar regolith was compact and reasonably rigid. Naturally he therefore believed the engine would dig a huge crater that would engulf the craft entirely. Fortunately Gold was in the minority, but it did come as a relative surprise just how quickly the lunar regolith compacted at depths lower than 10 cm or so. We know now why this is, but it was a surprise indeed. Probably been brought up before, but is it then fair to say that if knowledgeable people were perpetrating a hoax of Apollo 11, they would have dug out more of a crater under the LM? Was there serious mainstream concern prior to Surveyor that the lunar surface would be too soft to land/walk on?
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Post by Kiwi on Feb 18, 2010 8:26:27 GMT -4
What's the clash? The LM descent stage was still there after ascent. You can still see it there today in the LRO images. It's technically imprecise, and Eric welcomes and encourages even the smallest correction because he wants the ALSJ to be as accurate as possible. He is pleased to be told about a misplaced comma. From his biography page:Comments of any kind are appreciated. The astronauts and I want the Journal to be as accurate and accessible as possible. Besides, the caption could be confusing to a beginner. This is avoided by adding to or replacing the two "LMs" with "ascent stage" and "descent stage."
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Post by Grand Lunar on Feb 18, 2010 9:50:28 GMT -4
In all the supposedly elaborate things done to create a hoax I would suggest that digging a crater under the LEM would have been one of the simpler things if they thought it was required. And if the set designer forgot to dig said crater the last thing you would do is draw attention to it. So why would Armstrong describe the blast crater (lack of) as virtually his first act after stepping onto the moon? www.youtube.com/watch?v=d73jCthcAok&feature=related(5.48 in) Even before you have to do a bit of technical research to discover the actual downforce, the hoax proposition is a non sequitur. P.s I have seen 3 Harriers take off (vertically) from a grass strip and they never left a crater. If the hoax proponents say there should be a crater I want to see their homework, just saying it should is not an argument. Excellent find with the video. Armstrong does mention rays ementating from the engine. Which is probably all one should expect. Well, any rational person anyway.
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Post by PeterB on Feb 19, 2010 3:53:00 GMT -4
I've simulated the LM engine's effect using a spray can of insecticide and talcum powder a centimetre or so deep. Hold the can horizontally, and the plume of spray is a good mimic of the way the rocket exhaust would expand. It certainly blows away the flour, but in a scouring process, not by digging a crater.
Now this isn't to say this is a perfectly accurate recreation - the spray is wet and when you get close it soaks into the powder. But it's indicative. And anyway, the talcum powder smells pleasant.
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Post by randombloke on Feb 19, 2010 9:25:28 GMT -4
You are aware that you are generating an insane combustion hazard by doing that, right?
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Post by PeterB on Feb 19, 2010 9:45:55 GMT -4
In what way?
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Post by captain swoop on Feb 19, 2010 11:33:45 GMT -4
Your spray can will probably be using Butane as a propellant. Fine powder can cause 'flash fires' Flour Mills have been known to explode, they have lots of flash arrestors in their ductwork etc. I don't think there is a problem with Talc though it's pretty much an inert mineral.
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Post by randombloke on Feb 19, 2010 12:16:22 GMT -4
Depends on the brand of talc; an alarming number of them use scents with flammable aromatic components. Plus the high surface area:volume ratio increases the risk significantly.
You can easily test that with a gas hob (preferably outside and not near any flammable material) by taking a half-teaspoon of the stuff and using a long straw to blow it in the general direction of the flame. If you're careful you will get a cool fireball effect, just like the ones on TV. If not, you lose your eyebrows.
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