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Post by JayUtah on Nov 9, 2011 23:23:23 GMT -4
First read the top part of this page from the site. www.clavius.org/envheat.htmlWhen you say "it" was 225 F, you have to know what "it" is. In space it's possible for the sunny side of the spacecraft to be very hot, but the shady side to be very cold. When we say "225 F in the sun" we mean the part that the sun is actually shining directly on. The LM lands facing west, and the sun was behind them. The forward part of the LM is the cabin. The aft part, where the sun was shining, is all equipment. Look at this picture: www.hq.nasa.gov/office/pao/History/alsj/a11/AS11-40-5924.jpgThat's the rear of the ascent stage. If you took off the aluminum sheets you'd see a lot of the electronic equipment mounted there, on a rack attached to the back of the habitable cabin. There's really no way to move far enough back inside the cabin to get any heat from the sun. The problem with being wrapped in a rubber suit is that it doesn't breathe to let out perspiration. Without air circulating through it, the suit makes you sweat more. Then when air gets inside through the neck and wrist holes, it's cold and uncomfortable. I hope that helps. Heat transfer is a funny subject that goes against common sense.
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Post by ka9q on Nov 9, 2011 23:35:54 GMT -4
I've never understood the "can't change the battery" objection. The iPhone is designed to operate without any maintenance for the length of time that most purchasers are expected to use it, a little more than two years. Some people do use their devices for more than the battery lifetime, and they really resent the deliberate built-in obsolescence. Another reason to permit a user-changeable battery is to provide extra capacity when one cannot easily recharge the battery, such as on a long camping trip.
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Post by chew on Nov 10, 2011 0:02:40 GMT -4
Hello everyone, i am new to this website, and do not know any thing about the apollo landings, but i was listening to Buzz Aldrins book and he talked about trying to sleep in the LEM, but it was too cold, they even had on their space suits, and he says they were cold, they are wrapped in rubber suits and they are cold. he talked about opening the window shades to warm the lem, but the windows were on the shadow side of the lem, makes me wonder where he was? it was potentially 225°F in the sun, but the LEM was cold? maybe they should have scooted to the sunny side of the lem. I thought the problem on the moon was cooling not heating. Keep in mind an object has more surface area than the area receiving the sunlight. Take for example a box. A box has six sides. Sitting on the lunar surface only one side (for the most part) is receiving solar radiation and the other 5 sides are available to radiate that heat away.
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Post by ka9q on Nov 10, 2011 4:24:40 GMT -4
True, but there's another very important source of radiation: the lunar surface. Half of the sphere around the landed LM is occupied by the lunar surface, which emits blackbody radiation in the far IR range (10-15 microns) just as the earth does. The surfaces of both the moon and the earth reach equilibrium temperatures where the incoming solar power in the visible and near IR equals the blackbody radiation in the far IR.
The moon's blackbody radiation will tend to warm any object exposed to it unless the object is totally insulated by covering it with a material that appears completely reflective in the far IR region.
And the LM is in fact very well insulated. The descent stage is almost completely covered with very conspicuous thermal blankets of many layers of metalized Mylar that, in a vacuum, behave much like the walls of a thermos bottle. The ascent stage is also surrounded by thermal blankets, but they're generally hidden by thin metallic panels on spacers to form Whipple-type micrometeoroid shields.
The basic idea is that since the LM will be exposed to uncontrollable extremes of temperature, isolate it as much as possible from the outside. Since this also traps internally generated metabolic and equipment heat, active cooling is needed to get rid of it. That was done by vaporizing water into space in a sublimator.
The EMU (EVA suit plus PLSS) works on exactly the same principle: insulation plus active heat removal with a sublimator.
Although the LM was well insulated, it wasn't perfect. That's why Aquarius on Apollo 13 slowly got so cold. A secondary reason was that the sublimator had to continue dumping heat. I'm not sure exactly why, but apparently it was necessary to keep all the equipment at safe temperatures.
The astronauts also noticed the effects of lunar surface thermal radiation. There's a discussion of this observation at 132:01:20 in the Apollo 12 transcript in the Apollo Lunar Surface Journal. The crew and the journal editor were puzzled as to why the LM and suits seemed to gradually warm up on the lunar surface given that without an atmosphere the sun was at full brightness as soon as it rose above the horizon. I suggested that they were almost certainly feeling the effect of increasing lunar surface temperatures and far-IR thermal radiation.
All of the Apollo landings were in the early morning at the landing site, and even the long J-mission visits were over before local noon, avoiding the hottest surface temperatures and associated thermal radiation.
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Post by echnaton on Nov 10, 2011 10:23:37 GMT -4
I've never understood the "can't change the battery" objection. The iPhone is designed to operate without any maintenance for the length of time that most purchasers are expected to use it, a little more than two years. Some people do use their devices for more than the battery lifetime, and they really resent the deliberate built-in obsolescence. Another reason to permit a user-changeable battery is to provide extra capacity when one cannot easily recharge the battery, such as on a long camping trip. I understand that is the objection many people have, and for a some it represents real behavior. Many of the people I personally know who have made this objection are typical mobile phone users that get a new phone about every two years because of the vast improvement in successive generations. I'll skip the long Starbucks fueled analysis and say that it seems to be an aspirational objection rather than a practical one. That is people want to have a level of flexibility that they are very unlikely to use. But that and two bucks will get me another cup of Starbucks....
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Post by ka9q on Nov 11, 2011 6:54:54 GMT -4
My current phone is quite a bit older than 2 years, and it is not using its original battery. Even though I work for one of the best-known companies in the mobile phone development business, I simply haven't felt the need to buy a smart phone. I still use a beat-up Motorola RAZR. I'm about to replace it only because the screen has been blanking out increasingly often, probably because of a broken ribbon cable. And I got the RAZR only because my wife accidentally sent my previous phone through the wash.
I'm hardly anti-technology, far from it. It's that no smart phone and no tablet computer even comes close to doing what my laptop does. Since my laptop accompanies me everywhere, what's the point of also carrying a phone that does much more than make phone calls?
A secondary consideration is that I simply refuse to buy a locked-down computing platform when I can buy one that's open. Sure, I could probably jailbreak an iPhone easily enough but I see no need to reward Apple or anyone else with my business for that kind of fascist behavior.
When there's a smart phone that can do everything a late-model laptop can do, I'll consider one. That includes having a decent user interface, which seems highly unlikely in that tiny form factor until we develop Borg-style direct connections to the brain. So it'll probably be a while.
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Post by Apollo Gnomon on Nov 11, 2011 12:19:34 GMT -4
First of all, neither one is a thermodyanamics engineer, so the broad statements made for a general audience lack the weight of detailed analysis.
Second, there's no contradiction because the conditions described are not the same. Aldrin was talking about the actual temperature of the Eagle, which was set lower than for other missions (about 61 degrees) but Bean was talking about a hypothetical example.
Your confusion is caused by trying to make an apple into an orange.
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Post by JayUtah on Nov 11, 2011 13:44:02 GMT -4
Alan Bean says that if the LEM was in sunlight and if the starting temperature in the LEM was 70 degrees and climate controls were turn off, the temperature would continue to rise till 200 plus degrees. No. Well, not immediately anyway. With the sun low on the horizon behind the spacecraft, the rear-facing surfaces would become rather warm. But there are limited paths through which the heat will conduct forward. As the sun rises from there to its zenith (which takes a week on the Moon), more and more of the cabin would fall directly in sunlight and the internal temperature would rise. A week after that, the sun will shine more or less through the cockpit windows and the cabin air temperature would reach well over 100 F at least. Bean's estimate of 200 F seems a little high. Skylab's internal air temperature only got to about 125 F with its heat shield removed. Some parts of the LM were actually painted black or covered with dark material so that they would absorb enough heat from the sun. The LM propellants, for example, like to stay at roughly Earth room temperature. So the outer coverings around the tanks had a few black panels. Yes. First, you're falling victim to the frustration and confusion experienced by most beginning engineering students when they first encounter thermodynamics and heat transfer. It's not always intuitive, so it must be done ruthlessly by the numbers. Here's a very excellent free text book. web.mit.edu/lienhard/www/ahtt.htmlSecond, you're falling victim to conspiracy-theory rhetoric, which tends to respond with hysterics when it encounters anything that looks like an error or inconsistency. Before you think of crying fraud, stop and think whether there might be more information you could find that will fill in the gaps. Both, because they're talking about largely different things. Aldrin is speaking from experience, of course. Bean is speaking according to general heat-transfer understanding, but it's a deeper problem than one can really discuss in a brief interview for the popular audience. I'm not sure what you mean here. You've posted two quotes from individuals, not some general policy statement from NASA. Don't fall also into the trap of thinking that every time someone associated with Apollo opens his mouth, he's speaking on behalf of the agency and all its members past and present. Further, NASA provides an enormous amount of material on the design and construction of the lunar module, including its thermal performance analysis. That gives the engineering student plenty of information to ascertain whether the design may have been valid.
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Post by ka9q on Nov 11, 2011 17:04:21 GMT -4
Armstrong and Aldrin's problem with a cold cabin occurred with Eagle operating normally. The systems were running and the sublimator was dumping excess heat in the form of steam into space. Because of their complaints, changes were made to Intrepid, the Apollo 12 (Bean's) LM, to make the cabin a little warmer.
But the big difference is that Bean hypothesized "turning off the climate controls". I assume by that he meant turning off the sublimator while leaving the rest of the systems on. Without a way to dump waste heat from the equipment, crew metabolism and the relatively small amount of solar heat getting through the insulation, the cabin would warm quite a bit. However, before it could reach 200F the systems would probably fail and the crew would die and cease producing metabolic heat. That would leave only solar heating, and I don't know if that would be enough to actually reach 200F with the sun still low in the east.
A week after landing, with the sun overhead at solar noon, the surface will indeed reach temperatures in the 200F range. Its thermal radiation will certainly warm the LM even further. Now a totally passive object (batteries depleted, crew dead) each part of the LM will reach an equilibrium temperature. In a thermal vacuum chamber with the walls completely surrounding the LM at 200F, every part of the passive LM would also reach 200F. But the situation on the lunar surface is far more complex. There's the lunar surface at 200+ F and the sun overhead, but there's also the shadowed surface below the LM and the black lunar sky. It would take a sophisticated finite-element computer model to take all this plus the detailed design of the LM to determine the temperature of each part of the LM, some of which could be very high. Note that this does not contradict the very cold temperatures of Apollo 13's powered-down Aquarius because it was in yet another thermal environment: surrounded mostly by cold dark space, not the hot lunar surface.
So the bottom line is that you should not read too much into Bean's 200F figure. He was simply making the qualitative point that active heat removal was critical to keep the landed LM from getting too hot from the combined effects of equipment waste heat, crew metabolic heat, and lunar surface thermal radiation (especially a week later with the sun high in the sky). That's it!
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