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Post by ka9q on Aug 26, 2010 6:37:02 GMT -4
What scares me is if a certain other problem hadn't occurred, a malfunctioning sensor showed one of the oxygen tanks overfull, forcing them to stir and restir the tanks. Tjis likely hastened the accident to before the LM was undocked. I don't know for sure, but it seems likely that the reason the quantity sensor in O2 tank 2 was malfunctioning was because its wiring had been damaged along with that of the fan motor when the tank was emptied through the sustained use of its heater after the Count Down Demonstration Test. The Apollo 13 accident is one of the purest examples of how almost any major transportation accident these days is the result of not just one cause, but the final event in a long chain of coincidences, oversights and unlikely events. If not for the very serious consequences (and the fact that it really did happen) you'd almost have to laugh at the seeming implausibility of them all happening in just the right (or wrong) way.
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Post by supermeerkat on Aug 26, 2010 7:26:09 GMT -4
Can you imagine how Apollo 13 would have gone had the originally scheduled crew flown! A few months ago I was at Autographica, a British autograph convention, and Jim McDivvit was attending and had a 1 hour long Q&A session and it soon became apparent that McDivvit didn't like Al Shepard who he described as a "f****** idiot", who was "lazy", "spoilt", "attention seeking" and "relied upon other people to carry him". The subject of the 13/14 mission swap was bought up and McDivvit replied "had Shepard been present on Apollo 13, his stupidity would have killed them all", as Shepard "was under prepared" and "ignorant to the finer details of the Apollo program". But then, McDivvit and Shephard didn't really get on. So I'd take that with a pinch of salt. Also present were Fred Haise and Vance Brand, who I also attended a Q&A with. I took notes when they were speaking and must rememer to write them up and put them online sometime.
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Post by echnaton on Aug 26, 2010 9:34:37 GMT -4
What I have read about Shepard is that he was a more seat of the pants type pilot than most of the other astronauts. He relied on his exceptionally good skills and extreme self confidence, rather than technical knowledge. One piece I read (don't remember which one) discussed how he relied on Ed Mitchel to decipher what Houston was telling him during the hold after LM separation. As LM pilot, Mitchel of course would have been more conversant in the LM details, but the author suggested that Shepard was less prepared than he should have been.
Yet Shepard self confidence was such that he was prepared to land the LM under almost any circumstances. A seat of the pants kind of test pilot. After all his naval experience included flying Banshee night fighters off a carrier. Not a career move for those with a confidence problem. And he did make the most precise touch down of all moon landings, despite only getting radar lock on the surface very late in the landing. One wonders if he really would have tried to land without the radar?
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Post by banjomd on Aug 26, 2010 12:07:09 GMT -4
... One wonders if he really would have tried to land without the radar? In Moonshot Shepard tells the story and one garners the opinion that they were going to attempt the landing. Slayton was convinced that Shepard would not abort. Others (Kranz?) have stated that they would've run out of fuel before the touchdown.
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Post by supermeerkat on Aug 26, 2010 12:42:33 GMT -4
One wonders if he really would have tried to land without the radar? I recall reading somewhere that Mitchell believed that he would attempt it; McDivvit was of the opinion that doing such a thing was suicidal.
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Post by laurel on Aug 26, 2010 13:05:46 GMT -4
In Moonshot Shepard tells the story and one garners the opinion that they were going to attempt the landing. Slayton was convinced that Shepard would not abort. Others (Kranz?) have stated that they would've run out of fuel before the touchdown. Gene Kranz said, "[Gerry] Griffin and the Trench were convinced Shepard would have run out of fuel before landing. But everyone who knew Al never doubted he would have given it a shot. We also never doubted he would have had to abort. The fuel budget was just too tight." Failure Is Not An Option, page 351.
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Post by echnaton on Aug 26, 2010 13:52:28 GMT -4
I also wonder if he would have disobeyed an order from Houston to abort before the fuel situation became critical. He was an interesting character, a charismatic and brave man.
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Post by banjomd on Aug 26, 2010 15:31:21 GMT -4
I also wonder if he would have disobeyed an order from Houston to abort before the fuel situation became critical. He was an interesting character, a charismatic and brave man. I've taken an interest in "The Icy Commander" and, knowing what he did to get back on flight status and finally have a shot at being the only member of the Mercury 7 to walk on the moon, there is no doubt, in my opinion, that he would land or die trying! Abort was out of the question. As he said to Mitchell (after the landing) when asked if he really would've tried to land without the landing radar, "You'll never know!"
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Post by cos on Aug 26, 2010 16:39:08 GMT -4
I was lucky enough to meet Al Shepard at signing of Moonshot. I asked him that very question, given his experience as a Naval aviator, landing on carrier decks, day or night, in all weather, surely after going all that way he would have attempted to land on something as large as the moon without the radar? He grinned a huge grin and said he agreed it was an awful long way to go to just to come home but we'd just have to keep guessing. And I suspect he never said anything different.
I really enjoyed meeting him and was left with the distinct impression that the casting for the film "The Right Stuff' was spot on in his case.
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Post by fireballs on Aug 26, 2010 17:00:06 GMT -4
@fireball Thats one point. The other, and thats why I brought up the whole topic of satellite TV, is: There is little margin for pointing errors. Communication at those distances doesn't work like the one you are used to: For your radio receiver a simple wire put somewhere is sufficient to enable the receiver to catch the signal. Hack, here in Austria I even received TV by using my bunch of keys hooked up with a modified paper clip to a TV-set in 'emergency situations' and it did work. Not perfect, but it did work. But none of this will work at those distances and with those transmitting power levels involved from the mooon. Either your dish points more or less exactly at the source or you won't receive anything. 1 Degree off axis (probably less) -> silence. And that is the same for satellite TV and for communication with the Moon. So it is not the case, that the russians (and anybody else interested in receiving the signals) could just say: somewhere in that general direction of 45° around that spot the source must be located. The can precisly say: In that direction and nowhere else. And the russians would have been the first to cry, if that direction wouldn't be the direction to the moon.The guys operating the russian antenna dishes would have become very quickly very suspicous if they can see the moon high above them in the sky and yet they have to point there antennas at the horizon to get the best signal quality. If that would have been the case, then the signal source is located at a line along the horizon and there is no way it ever could come from the moon. Same, if the signal source moves in a different way then the moon moves in the sky. All of this of course does not proove that manned Apollo capsules were at the moon. But it proves that at least some source for radio signals must be located on the moon. And this source must have been brought to that location. With a rocket. And since it is impossible to fire a rocket without the russians knowing it ... it must have been Apollo, which brought that radio source to that location, since there is no evidence how else it could have gotten there. There is a lesson in it: While there is no single 100% proof, that Apollo indeed brought man to the moon, all the evidence in their totality point to only one possible conclusion: they went where they said they went. You earlier asked and the answer is pretty simple: Because it is the only way to simultaniously come up with all the effects we can see, hear and measure in the Apollo documentation. Assume a fake and the problems begin. You can get away with assuming this and that part was faked. But then you run into enormous problems in other areas. Actually: Looking at all the problems creeping up, it is far easier to simply go to the moon. Don't get me wrong. Going to the moon is no easy task. But compared to the difficulty level of faking it with all physical and logistic aspects, it is as simple as taking candy from a baby. I was thinking more about this, and yes it still makes sense to me. But can someone either explain this to me or refer me to a site that explains this? (see bold)
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Post by Jason Thompson on Aug 26, 2010 17:48:15 GMT -4
What are you having trouble with, specifically, fireballs?
Terrestrail radio and TV broadcasts are omnidirectional and in fact the signals reflect off the different atmospheric layers so they can still be received even if you are not in a direct line of sight with a transmitter.
Radio transmission from the moon are not omnidirectional. They are transmitted from the Moon to the Earth, and the limited power of the transmitter plus the normal divergence and resultant weakening of the signal means that you need very sensitive receivers to pick up the signal by the time it reaches Earth, a quarter of a million miles away. These receivers are directional, much like telescopes are, and that means that in order to receive a transmission from the moon you have to aim them at the Moon. It also means that if they are aimed at the moon they won't pick up signals from anywhere else, so the transmissions received by a dish aimed at the Moon can ONLY be coming from the Moon.
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Post by echnaton on Aug 26, 2010 20:34:52 GMT -4
Perhaps it is the parabolic dish that is troubling you. A parabola is a specific geometric shape with a special property that makes it especially suitable as an antenna. Think of a dish antenna pointing straight up, with X as the horizontal and Y as the vertical. All radio waves hitting the dish parallel to the Y axis will be reflected to a common point, called the focus of the dish. At that point there is a collector to take the waves and put the signal on a cable to go to a receiver, like any other antenna.
Waves coming from any angle other than parallel will be reflected elsewhere. Whats more the geometry is such that the larger the dish the further non-parallel signals will be reflected from the focus. So a "pizza pan" dish like they use for satellite TV will still function even if not perfectly aligned while the huge radio astronomy dishes used to track Apollo have a very low margin of error.
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Post by JayUtah on Aug 26, 2010 20:49:53 GMT -4
But can someone either explain this to me or refer me to a site that explains this? (see bold) Sure. You're probably used to radio waves going in all directions, like they do from a TV or radio station transmitter. That's not how radio waves work for dish antennas. Dishes transmit and receive along a narrow path. At the S-band wavelength, a radio telescope beam width is about 1/3 degree. That is, it's a very narrow cone extending from the dish outward. Anything to which you want to transmit has to be inside that narrow cone. Any radio source you want to receive from has to be within that cone. If it strays outside, you lose the signal completely.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Aug 26, 2010 21:01:38 GMT -4
At the S-band wavelength, a radio telescope beam width is about 1/3 degree. For comparison, the diameter of the Moon as viewed from Earth is about 1/2 degree. So you can see that the antenna beam width is narrower than the size of the Moon. If the signal was not coming from the Moon it would be immediately obvious.
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Post by PhantomWolf on Aug 26, 2010 21:27:44 GMT -4
What scares me is if a certain other problem hadn't occurred, a malfunctioning sensor showed one of the oxygen tanks overfull, forcing them to stir and restir the tanks. Tjis likely hastened the accident to before the LM was undocked. This was all part of the same problem, it is believed that the damaged sensor shorted out resulting in the off the chart high reading for the same reason that the stirrer then shorted out cuasing the explosion. But yes, if it had not, then the explosion would have likely occured when in Lunar orbit with the LM on the surface. Of course even if it hadn't undocked, the LMME didn't have the power to have broken Lunar Orbit with the entire stack.
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