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Post by ouloncollouphid on Aug 31, 2005 18:32:48 GMT -4
Well, in that case, why was I invited to contribute to another thread?
Well, that is interesting. I must confess that it is kind of fun when HBs like yourself are baited, fun to marvel at the flights of fancy and outrageous disregard of sense and logic displayed. All very entertaining.
But more seriously, as Jay and the others have explained many times, it is important to counter the HBs, in order to expose their ludicrousness to any lurkers observing.
I am mainly a lurker myself, but sometimes I can't resist.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Aug 31, 2005 18:46:33 GMT -4
Margamatix, I'm still waiting for you to tell us why the PLSS cooling system wasn't up to the task. Please derive for us how much heat "that" is and explain why the cooling system was incapable of rejecting it. Clearly you already have the answers to these questions or else you would not have been able to say the cooling system wouldn't do the job. So please don't delay any longer and explain it to us.
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Post by hubcapdave69 on Aug 31, 2005 19:08:27 GMT -4
All right, Marga. I am a layman when it comes to this, same as you. that being said, I see the flaw in your arguement very clearly. It shows in your goldfish example.
You used the adjective "ambient" to describe the tempurature on the moon, and your fish example would be an example of "ambient" tempurature. The term ambient means "existing on all sides" (from the latin term meaning "to go around"). You can have an ambient tempurature on Earth because there is an atmosphere, there are gaseous compunds which you can heat up or cool off. The moon doesn't have an atmosphere. No gaseous compunds to heat up or cool off. The only things that get heated or cooled on the moon are surfaces. There would be no ambient tempurate because there is nothing past the surface of the moon to heat up! Therefore, all you have to cool off is the effect of the surface of the spacesut being heated up and raising the ambient tempurature inside the suit (the inside of the suit does have an atmosphere, so it would have an ambient tempurature). Since it dumps heat into a vacuum, it has no outside tempurature to deal with!
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Post by Mr Gorsky on Aug 31, 2005 19:34:29 GMT -4
Hence the outside of the suit is white, which (very effectively) reflects away a great deal of the light from the sun, thereby ensuring that the ambient temperature within the suit is kept at a manageable level.
Margamatix, you gave a perfect example of why posters here get frustrated dealing with your arguments. You wrote ...
... yet you offer absolutely no justification whatsoever for your assertion that the backpacks would have been unable to do this, and state it as though it were a simple and irrefutable fact.
Other posters (who actually understand and work with the technologies involved here) have pointed out to you in great detail how and why the PLSS would have done this job without any problems at all.
You then further sully your entire argument by talking about it being "overwhelmed by the ambient temperature", when even I know that you need an all-encompassing medium (such as water or an atmosphere) in order to have an ambient temperature.
As others have mentioned many, many times already, if you put forward an unsupported argument, such as this one, then receive a detailed, scientific response outlining how and why you are in error then you cannot just ignore that response and simply restate your argument. You must address the issues raised which cast doubt on your argument, lest you be branded a troll.
If I buy a car which the previous owner claims to be a Ferrari, and others (with greater knowledge of cars than I) point out all the reasons why it is actually a Volkswagen Beetle, I cannot just continue to claim that I own a Ferrari without addressing those points.
Well ... I can. But I would be an idiot!
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lenbrazil
Saturn
Now there's a man with an open mind - you can feel the breeze from here!
Posts: 1,045
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Post by lenbrazil on Aug 31, 2005 20:15:32 GMT -4
Well, in that case, why was I invited to contribute to another thread?
Because you were invited by someone who just registered on this forum yesterday and hasn't dealt with your BS like the rest of us.
I asked you and other HBs I named you specificlly because you stood out as the most prolific HB here
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lenbrazil
Saturn
Now there's a man with an open mind - you can feel the breeze from here!
Posts: 1,045
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Post by lenbrazil on Aug 31, 2005 20:22:41 GMT -4
Would you debate some one who believed in the 1st 2? How would react if they rejected out of hand every resonable argument you made? 1) No 2) No 3) No 4) Don't know. 5) Yes I am flattered to have become such an object of attention, but could I just ask that in future you start more generalised threads, as I do not have the time to answer everybody on every thread which is specifically directed towards me- thanks.
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lenbrazil
Saturn
Now there's a man with an open mind - you can feel the breeze from here!
Posts: 1,045
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Post by lenbrazil on Aug 31, 2005 20:36:42 GMT -4
I am not sure. I was hoping someone better informed would answer. My guess is that since it's surfaces [and what lies beneath them] that get hot or cold up there if you were on the dark side you'd freeze your butt [bum for your Brits] off! If you you were on the bright side you'd be quite hot. The side of you directly facing the sun would feel hotter than the side of you receiving solar radiation being reflected off the moon's surface. It's that same reflected radiation in the form of light that so confuses HBs like Jack White. Len So if you stood naked on the moon, but insulated from the surface, would you feel very hot or would you feel very cold?
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Post by rocketdad on Aug 31, 2005 22:51:48 GMT -4
I'm not a scientist, but I think I can explain heat a little better and less tecnically. Forgive my Farenheit handicap, I'm a Yank.
First, get the fish out of the boiling water, that analogy is all backwards, and the SPCA will slap you.
The single word "heat" means two different things: the vibrations of the molecules of a substance, and the infrared part of the electromagnetic spectrum which contains, but is not only, light.
The human body is a Snickers-powered meatcandle illuminating the universe in the infrared spectrum. The human body is intrinsically lazy as a survival tactic and wants to illuminate as little of the universe as possible.
What the human skin senses as heat is several things. One is the temperature of the surface of the skin. One is the amount of difference between skin temperature and body core temperature, or to put it differently, how much heat you are dumping. A fever is confusing to the body, because the skin is hotter than normal human surface temp, and it sometimes "feels" hot, but the skin is colder than the room so you "feel" cold. This is all comparative information, not absolute like a thermometer.
The skin also detects light in the infrared spectrum. Don't believe me? Close your eyes and see how close you can get to a lightbulb without touching. Your hand is detecting the infrared light coming from the filament.
That is called "radiant" heat.
Cut up a carrot, put it in a skillet and turn the stove on High. The carrots are not 1500 degrees. The pan is not 1500 degrees. The flame under the pan is gas vibrating and radiating at 1500 degrees, (round terms, no nit-picking please) and it has to transfer by conduction (flame surface touching pan) convection (flame heats air, air flows across pan) and radiation (flame emits light, more is absorbed by pan than reflected).
There is no oil on the carrots. The pan overheats and the carrots scorch. Adding oil increases the surface area contact between the hot pan and the cold carrot. The greater the delta-T (difference between 2 temps) the faster the heat flows through whatever is conducting or resisting. R13 insulaton conducts at 1/R, or one divided by 13. R13 insulaton is a U0.077 conductor. Hot oil conducts the 500 degree heat to the 40 degree carrots, and they stir-fry up nicely.
The sun is a giant lightbulb, emitting radiant heat. In August here in Colorado the afternoon surface of a car can be 150-plus degrees on a 90 degree day. Overnight the air cools to, say, 70 degrees. The car is 70 as well. We call this "ambient" temperature. There is no ambient temperature on the moon, as no heat can wander from place to place by convection and conduction.
In the lunar "morning," the lunar dirt is really cold. It has radiated heat from the previous "day" out into deep black space where nothing reflects any infrared back. The sun beats down, and over a month warms the lunar dirt to a temperature that others quote to be 250 degrees. I don't have the references to look it up, so lets just say it's so.
How long did it take the pan on your stove to warm from "ambient" room temperature to 500 degrees? How long did it take to cool down to ambient after you turned it down? These are a function of conduction to air, convection carrying hot air away and bringing more cold air in, and by radiation of infrared light to the room. Most of the kitchen absorbs the light rather than reflecting it back to the pan. A volcano is much more dangerous than space, as you can see.
So in the vacuum of space the only way heat normally leaves a thermal mass is by radiation, since no conduction and convection are available. A better analogy than putting a fish in boiling water is to put a fishtank in a cold room and give it too small of a heater: the tank is dumping heat to the room faster than the room and the heater are adding heat to the tank. Fish die under these conditions by snuggling the 150 degree heater in the 60 degree tank trying to be 78 degrees of cozy.
Heat the pan again, then dump really cold water on it. Some of the water immediately boils, but the pan cools down very quickly.
I think the space suit coolers used wasteful techniques like spraying the radiating surface with something that carried heat away to the universe at large.
If you don't understand what I've said, ask specific questions, not general.
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Post by PhantomWolf on Aug 31, 2005 23:45:04 GMT -4
So if you stood naked on the moon, but insulated from the surface, would you feel very hot or would you feel very cold? Neither, you'd be dead. Why? Because there is no air, thus you'd suffocate. Of course after that your corpse would most likely freeze. The reason here being that since the surface of the moon can't transfer or radiate heat to you directly or indirectly we can ignore it totally and treat the situation as if you were just out in space. Out in space there is no ambient temperature because there is nothing to -have- an ambient temperature. Without air or water or something, there is nothing to heat up. While the human body is avaiiable in many wonderful colour tones from deepest black/brown to paleass white we'll pick the colour most astronauts were, sort of beige. That's a light colour and so is reflecting a lot of light and radiative heat from the sun. meanwhile the water in the skin and body is esentially boiling and removing heat. The body loses more heat through that action then it gains directly from the sun's IR radiation and so the overall temperature drops, eventually freezing the corpse. Now let's consider the situation if we remove the insulation about the person so the lunar surface does play an effect. Now it depends on the time of Lunar day, so let's cover the entire 28 Earth days that it takes for the Moon to have one day pass. Again the person is dead because there is no air. Once more we have no atmosphere and so no ambient temperature to deal with, thus we only have two sources, the Sun, and the surface. The Sun reacts the same way as before, mostly being reflected away from the corpse, however this time we have an additional source as well, the rock. Now starting at dawn the rock will be extremely cold, this is because, like the corpse in out last example, the surface of the moon is radiating more heat as IR than it gets back without sunlight hitting it, so it's nett energy is a loss and it cools, and so it will drain heat directly from the corpse lying on it. Thus the contact with the rock will freeze the body. Of course as the Sun comes up and the angle gets bigger, more sunlight hits the rock, thus starting to balance out the IR loss with that gained by the Sun. At a certain point they cancel, then the Sun is high enough that the surface is gaining more IR than it is losing. At this point, with the Sun bearing down, the surface will begin to warm, but it's not an instantanous thing, the rock heats slowly so that throughout the morning it goes from freezing to bearable to hot until by midday it's very hot. Now our body is getting a lot of heat transferred from the rock both by radiation and directly. This will heat up the corpse, thawing, and then frying it, again it's not instantaneous but takes time. As evening comes, the amount of sunlight hitting the surface decreases due to the angle, and the surface once more starts to radiate more heat then it is getting Thus while still hot, it starts to cool down and as the sun gets further away and finally is blocked by the horizon, the rocks cool faster. So does our corpse. With total darkness they both head towards freezing again. And so the cycle will continue. Now let's consider our Astronuats. What do we have to do for them. Well thay need air to start with, so let's give them a pressure suit. Now that they can breathe, what type of heat do we need to protect them from? The sun's IR and the ground's IR will be hitting them everywhere, and any direct contact with the ground could cause a problem. So how can we minimise it? Well since the ground doesn't heat up instantly, nor does it cool instantly, we could have them there when the ground hasn't heated up too much, but isn't frozen, or we could have them there when it's not extremely hot, but hasn't cooled to freezing, that would help a lot. Okay so when do those occur, well the first is early to mid lunar morning, the later is during the late evening night. Because we don't want them landing and working in the dark, we'll send them so that they land during the lunar morning at the site of interest. (which funnily enough was when they did each of the landings.) Okay so that is one thing that is minimised, what else can we do? How about we add some layers of insulation to prevent heat escaping from our astronauts, or entering them, that way if they do touch a rock that is hot, or cold, they won't burn themselves. Sort of like you do with an oven mitt on getting a roasting dish from the oven. How about we also protect them from the IR from the sun and surrounding surface? To do that we just need to add a reflective layer. White's pretty good for that. So we have a white overlayer, insulation layers and a pressure suit. Want to compare that to what they actually used? Okay so now we have protected our Astronaut from the enviroment, we have a problem. You see on Earth, our bodies cool themselves by sweating, the excess heat is removed by vapourising the water into the air. Inside a suit, that air quickly warms up and saturates until no more sweat can be evaporated and so no more heat can be lost. That means we need a way of getting the heat out of the suit. See, this is what the PLSS was for, not protecting the Astronuat from the enviroment, but getting their body heat out of the suit. By running a series of tubes about the body in an undergarment we can run cold water through them. The body heat, heats the water, reducing the body's temperature.That's handy, but we still have hot water after a while, so we need a way to cool it. Well we can run it through a heat exchanger, but all that does is move it from one system to another, it doesn't expell it. But wait, remember I said way back in the space corpse example that the water in the skin and body would boil taking away the heat? We could use the same system. By boiling water off into the vacuum of space we could remove the excess heat from the suit. Unfortunately that takes a lot of water because when exposed to a vacuum, liquid water just boils away without added heat. However, there is a special type of porous metal which water can seep through very slowly, and when it just coats something, water forms into icecrystals when in a vacuum, it doesn't just boil away. This is very useful because if we can just dribble the water through the plates of the exchanger, they will cover it in ice, and since ice requires more heat to subline that water takes to boil, we can remove even more heat. That means that the heat in the cooling water can be transfered to the ice and in subliming it, that heat will be removed giving us cold water again to recirculate. Excellent, we now have a way to remove the excess heat, a system so efficent and effective, that it was used by the Gemini crews during their space walks and is still used by the Shuttle and ISS crews today, 40 years later. This is how the PLSS works, it relies on it being inside a vacuum. It wouldn't work in an atmosphere or underwater, it requires that the ice can sublime and take the heat with it. This is why it's great for space walks and EVA's on the moon, there is no atmosphere. It's also why it's totally different to an air conditioning unit and can't be compared to one or to the "goldfish" idea. The goldfish is in water, not a vacuum, and an airconditioner works with exchanging heat between air going in and coming out. Totally different systems.
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Post by PeterB on Aug 31, 2005 23:58:51 GMT -4
Margamatix
Think about this. The spacesuits used by the astronauts on the Space Shuttle for spacewalks are based directly on the suits used in Apollo. Both suits operate in a vacuum. Now if the Space Shuttle suits work, why wouldn't similar suits work on the Moon? It's no hotter there than in direct Sunlight in Earth orbit.
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Post by rocketdad on Sept 1, 2005 0:22:00 GMT -4
I'll go back to the fish-suit now for a moment: the suit is designed to protect the fish from the heat input of the boiling water. The inside of the suit is 78 degrees, the outside is 212 degrees or less. The cold side of the heatpump needs to be colder than 78 by goodly amount (call it 58, for a delta-T of 20 degrees, not so cold it chills the aquanaut) and hot side needs to be hotter than the boiling water by a goodly amount.
The greater the difference in temp the faster the transfer happens, so lets call it 300 degrees. Ignoring the heat of the radiator conducting back thru the fish-suit, an ordinary heat pump could help an explorer-fish survive a dangerous journey in the soup-pot. I'm not a qualified engineer to provide specifics, I'm just a guy who actually understands how the refrigerator keeps my milk cold. The cold air at the back of my fridge is about 20 degrees, and the milk in the door averages 45. The surface of the fridge is about 2 degrees colder than the room.
I love my point-and-click laser thermometer! Can you tell?
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Post by PhantomWolf on Sept 1, 2005 4:40:41 GMT -4
margamatix,
In response to both rocketdad and my longer posts above, I'd like you to answer few questions.
1) Explain the three types of Heat Transfer, Radiation, Convection and Conduction. 2) Explain which ones can occur on the Moon 3) Explain what "Ambient Temperature" means 4) Explain the difference between Heat and Temperature. 5) Explain the what a Phase Diagram of Water is. 6) Explain why water boils at lower temperatures when in lower pressures. 7) Explain what sublimation is, and why it requires more energy than boiling.
These aren't actually hard concepts, they are expected to be known by 1st Year University students, if not before (Phase diagrams are taught here as early as in year 10 science, or at least were when I was at school.) If you learn about these things and understand them, then you will understand exactly how and why the PLSS works.
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Post by sts60 on Sept 1, 2005 13:44:28 GMT -4
OK. On the moon, it is either very hot or very cold (the astronauts seem to be confused about which it is).
No. You seem to be very confused about which it is; the astronauts, scientists, and engineers understand it quite well.
Your problem is that you are thinking only in terms of temperature on Earth, where you are immersed in an atmosphere, and therefore have to deal with convective heating/cooling and evaporative cooling from the body. You are also generally not well isolated from heat transfer to objects via conduction.
The situation is entirely different on the Moon, where there is no convective heat transfer at all, and conductive transfer is minimized by efficient insulation. There is no such thing as a single "ambient" temperature on the Moon. There is the temperature of various objects, which depends on the phase angle of solar insolation (how directly sunlight is striking the object), the object's emittance and absorbance (how fast it emits and absorbs heat via radiation), and the integrated heat input over time. If you look at a certain lunar rock in mid-lunar-day, it might be as high as 250C. If you look at another rock in shadow, it might be 0C. If you look up at the stars, the tempeature is about -270C.
Unlike Earth, there is no medium (i.e., air) which tends to equalize the temperature of things and serves as a reference "ambient" temperature. And even on Earth, the temperature of things is not the same - on a hot summer day, you can walk on nice cool grass or burn your feet on the asphalt.
Assuming it is very hot, then the backpacks would have been unable to reject that amount of heat for that duration of time.
Handwaving. Where are your calculations to show this? What expertise do you have to make this judgement?
Whatever coolant they used, it would have been overwhelmed by the ambient temperature.
They used water, and it rejected heat from the suit via sublimation. The heat of sublimation of water is roughly 50 kJ/mol, or 2.6 kJ/g, or about .73 Wh/g. The human body generates roughly 100 W of heat. Assuming the suit - which is well-insulated from conductive loss or gain to the ground, and is highly reflective to reject solar radiation - neither gains nor loses heat, it would theoretically take about 130 g (roughly 1/3 lb) of water per hour to cool the suit via sublimation. The actual values were considerably higher - the ALSJ says about 12 lbs of water were used to give 8 hours of cooling for "fairly strenuous" activity, about 3/2 lb per hour.
That's why air-conditioning units are the size they are, in order to perform such a small reduction in temperature.
Comparing an air-conditioner used to cool a room or house on Earth to a sublimative unit used to cool an astronaut on the Moon is not a valid comparison. Not even close.
Let me put it another way......
Design a PLSS for a goldfish which is to be immersed in a gallon of boiling water for three hours. The maximum mass of the PLSS is to be no more than 25% of the mass of the goldfish.
This strawman reflects a fundamental ignorance of the lunar environment. The heat transfer problem is entirely different. There is no convective heating or cooling on the Moon.
I'm glad you attempted to defend one of your technical claims. Unfortunately, your defense fails, because you have completely misunderstood the underlying physics.
Do you concede the point, or do you need further explanations?
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Post by papageno on Sept 1, 2005 14:04:14 GMT -4
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Post by JayUtah on Sept 1, 2005 14:49:16 GMT -4
Maybe in the sense that a drowning man could benefit from a swimming textbook.
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