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Post by banjomd on Mar 25, 2010 17:00:06 GMT -4
The dust follows a ballistic path.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Mar 25, 2010 17:29:47 GMT -4
Quick question on the Lunar Rovers. One of the films shows the rover going round and the comments on the 'rooster tails' heard on dialogue. The contention is that this is THE thing that shows an atmosphere since the dust hits something that can only be a wall of air and falls to the ground. I kind of see what he means, but am not sure....what do you guys think? There was an excruciatingly long thread about this a couple years ago if you can stand reading it: apollohoax.proboards.com/index.cgi?board=theories&action=display&thread=1009In essence, the claim is bunk. People who think they’re seeing non-parabolic trajectories are just being fooled. The particles follow the ballistic paths expected in an airless environment. Furthermore, if the particles are small-grained enough to be effected by the air in the way you describe, then they are likewise small enough to aerosolize. We would, therefore, see the formation of dust clouds. The claim is internally inconsistent.
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Post by Jason Thompson on Mar 25, 2010 19:00:39 GMT -4
The contention is that this is THE thing that shows an atmosphere since the dust hits something that can only be a wall of air and falls to the ground. I kind of see what he means, but am not sure....what do you guys think? I think that every time we have someone here arguing that the dust shows suspicious behaviour, they always think that they can look at a cloud on the film and assume it is coherent and can be treated as a single ballistic entity. That is not valid, because you just can't see the dust clearly enough. What is clear is that this dust, which they claim can be stopped by the air, does not create big billowing clouds of dust. It cannot both be slowed and halted by the air to fall straight down and be too heavy to aerosolised.
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Post by JayUtah on Mar 25, 2010 19:54:07 GMT -4
The contention is that this is THE thing that shows an atmosphere since the dust hits something...No. The notion that it stops abruptly is an interpretational notion apparently reckoned because the forward motion of the rover engenders some expectation of commensurate rearward motion in the plume. Since the plume often disperses not long after reaching its apex, it's difficult to track it accurately. ...that can only be a wall of air"Can only be" is the other interpretational shoe dropping to the floor. The claim, as stated, blatantly begs the question. They want to prove there is air, so they inexplicably declare that "air" is what's causing the observation they see. ...and falls to the ground.Yeah, that's the problem. As Bob has noted, and as I concur, if there is air and the particles are small enough to be abruptly stopped by it, then they would aerosolize (i.e., form clouds). The two observations are the same phenomenon at work. You can't separate them. You can't argue that the dust is slowed immediately by the air in the horizontal dimension, but impervious to air resistance in the vertical dimension (i.e., falls immediately to the ground). The hoax believers imply a model for aerodynamics whose only virtue is that it conforms to their interpretation of the observations. It doesn't actually describe a valid physical process for how particulates and air interact. Yet upon this presumptive model the hoax believers dismiss the validity of the film. As with all their other expectations that purport to derive from physical behavior, it's simply made up.
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Post by PeterB on Mar 25, 2010 20:00:25 GMT -4
Quick question on the Lunar Rovers. One of the films shows the rover going round and the comments on the 'rooster tails' heard on dialogue. The contention is that this is THE thing that shows an atmosphere since the dust hits something that can only be a wall of air and falls to the ground. I kind of see what he means, but am not sure....what do you guys think? G'day Capricorn1 What do you think they mean by that statement? Literally a wall made of air? That trails around invisibly after the rover? I've never heard anyone explain it in a way that makes sense. Anyway, have you ever driven on dirt roads? I have, and I've watched plenty of other cars drive on them too. If you drive on a dirt road here on Earth, you throw up a cloud of dust. Look out the rear vision mirror and you'll see the dust hangs in the air for hundreds of metres behind you. That's because the dust particles are so light that they're easily carried by the air. I've also watched rally cars driving along a dirt track on the side of a hill, and seen the dust clouds gradually drift down the hill. You never see dust clouds like this on the Apollo footage. Very well, say the Hoax Believers, the rovers are driving on sand. But sand contains dust too, so that doesn't work. Also, we see the rovers leave clear tracks in the ground, which only works with powdery dust. You can't have a surface which is like powder when it's driven on, but throws up only sand. Okay, say the Hoax Believers, so it's mud they're driving on. That preserves tracks and would explain how the material thrown up by the rovers' wheels falls down to the ground. Except that there isn't any sign that the ground the astronauts walk on is wet. There are no splatter marks, and there's plenty of footage of astronauts interacting with the ground (kicking it, digging in it, falling over onto it) that show it's completely dry. So what are we left with? Either this footage was filmed on magic ground which becomes powder, sand or mud, depending on the need at the time, or it's powder filmed in a low gravity vacuum, otherwise known as the surface of the Moon. I can't think of any alternatives.
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Post by PeterB on Mar 25, 2010 20:06:13 GMT -4
I can't think of any alternatives. Actually, now that I think of it, I can - a low gravity Vomit Comet trajectory in which the air has been removed (easier, perhaps, if flown at very high altitude. Of course, then, you have other problems - you can't film more than 30 seconds of footage at a time, and you won't be able to hide the fact that you're filming in a plane, particularly if you're trying to film a car driving a 30 metre wide circle while standing 30 metres away (or whatever the distances are). The thing is, we have footage of astronauts practicing activities in a low gravity Vomit Comet, and while the gravity effects are obvious, so too is the fact that they're in a plane.
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Post by capricorn1 on Mar 25, 2010 20:26:04 GMT -4
Satisfacory answers to my question. The contention is indeed piffle.
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Post by banjomd on Mar 25, 2010 21:05:22 GMT -4
capricorn1, I think you're posing questions to the right people (myself excluded)! I've only been here a short while but I've learned that there are many empassioned and knowledgeable scientists here who will help you. Keep it up.
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Post by scooter on Mar 25, 2010 23:42:29 GMT -4
This "wall of air"...why doesn't the dust hit it sooner after leaving the wheel...or later? What is this "wall of air" they speak of, I'd love to hear an explanation of it, and how it's created. Never seen one here on Earth...in the atmosphere.
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Post by Data Cable on Mar 26, 2010 12:16:56 GMT -4
Re: The Rooster Tails hitting a "wall" of air: Don't be fooled into thinking that the formation of regolith particles kicked up by the wheels, as it appears in any single frame, represents a coherent "stream." i.e. the path followed by each individual particle. There may appear to be an abrupt "falloff" in the "arc," but this is likely just a greater population density of particles which happened to be ejected from the trailing face of the wheel a roughly the same time.
BTW, something else which struck me at some point about the "rooster tail" argument which I don't know was ever brought up. In one of the discussions (perhaps the one linked above, I haven't checked it) much was made of using the rover's top recorded speed to calculate a maximum rotational velocity for the wheels. However, it's possible the wheels were turning faster than that when the rooster tails were kicked up.
It was noted the tails occurred mostly when the rover went over large bumps. When that happened, some wheels leave the ground momentarily. A motor which has only to turn the mass of the wheel attached to it will turn faster than a motor which has to propel the mass of the vehicle (or 1/4 of it, anyway.) So the wheels which kicked up the tails, having been temporarily freed of their mechanical load, would have been spinning faster than the wheels which stayed in contact with the ground.
So the relevant value in calculating maximum arc height of any given ejected particle should be the free-spin limit of the wheel alone, not necessarily the highest recorded ground speed.
</threadjack>
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Post by capricorn1 on Mar 27, 2010 17:45:04 GMT -4
Question: Is space cold? I've read....yes it is about 3 degrees kelvin. And I've read.... no it has neither cold nor hot since it is basically a vacuum. I read Jay's temperature assessment on Clavius and it made sense, but didn't answer this point. How fast does heat radiate from a human body in space not just in the PLISS but also whilst on route to and from the moon. It may also have relevance if the Apollo 13 account of the astronauts being really cold on the way back is true (or is that just the film?). Also, is it true that the spacesuits used a water cooling system?
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Post by Jason Thompson on Mar 27, 2010 18:43:22 GMT -4
Question: Is space cold? I've read....yes it is about 3 degrees kelvin. And I've read.... no it has neither cold nor hot since it is basically a vacuum. This is a complex question. On Earth it is an easy question to answer. When someone says 'how cold is it?' they generally are referring to a specific object or the ambient temperature. But heat and temperature are different things. Temperature is a measure of the kinetic energy of a particular thing. It is therefore a property of matter, and space being a vacuum can therefore, by definition, have no temperature. What there is in space is radiation, and this will vary depending on your proximity to any emitter of such radiation (the Sun, for example). It is that which will play a key part in determining how hot or cold anything in space will get, and how long it will take to reach thermal equilibrium. Consider this: You could probably tell me how hot or cold it is in your town right now, but if I asked you how hot or cold Earth's atmosphere is, what would you say? Being picky, there is no 'I' in PLSS, it bieng an acronym for Portable Life Support System. It's a phonetic addition only to make it easier to say. The PLSS also refers specifically to the backpack, not the entire spacesuit. But your question about how long heat takes to radiate away from a human body depends heavily on so many factors that there really is no simple answer to it. That is quite true, but bear in mind Apollo 13 is a special case. The cooling of the inside was in part caused by the fact that the electronics that were still operating needed to be cooled actively to stop them overheating, so there was a system working to remove heat, but no cabin heaters or anything else warming it up at the same time. Yes. Enclose a human in a non-breathing material for any length of time and his opwn metabolic heat will rapidly make the environment unbreable, and will ultimately lead to overheating. It was quite apparent from the Gemini flights that the flow of air circulating inside the suit simply was not sufficient to carry away the excess heat, especially during physically demanding activities, and so a water cooled system was employed for Apollo. In the undergarment was ametwork of thin rubber tubes through which a steady dtream of water was running. The water was close to the astronaut's skin and was warmed by it. The water then passed into the backpack, where it passed through another device that used this warm water to heat up some water that was steadily streamed onto the outside of a metal plate exposed to space. This water froze in the vacuum, and then the warmth from the water inside transferred to this ice, causing it to sublime away. This effectively transferred the heat away into space, cooling the water in the tubes again so it could be recirculated to the suit and begin the process all over again.
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Post by capricorn1 on Mar 28, 2010 5:33:05 GMT -4
This should be easy to answer and the last part of this contention I'm not fully understanding. Was the radiation from the sun completely absorbed by the outer hull then (during transit)? And did the craft rotate slowly to avoid hotspots and assist cooling. Everything making sense so far.
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Post by HeadLikeARock (was postbaguk) on Mar 28, 2010 6:25:33 GMT -4
This should be easy to answer and the last part of this contention I'm not fully understanding. Was the radiation from the sun completely absorbed by the outer hull then (during transit)? And did the craft rotate slowly to avoid hotspots and assist cooling. Everything making sense so far. Only a theoretical ideal black body would completely absorb all radiation falling on it. The surface of the CSM was quite shiny in order to reduce absorption of radiation. Note it is only reduced, not eliminated. The CSM did indeed perform a maneouvre referred to as a "barbecue roll", which pretty much did exactly as you described: avoids hotspots and assists cooling.
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Post by banjomd on Mar 28, 2010 7:54:17 GMT -4
When you see "PTC" they're referring to passive thermal control which is the "barbecue roll". Correct me if I'm mistaken but it is only needed in the coast-phases due to the uninterrupted solar radiation for days.
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