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Post by ka9q on Feb 18, 2010 19:35:08 GMT -4
Either the "hoax community" is very small or they talk with each other constantly, because in the past few days I've also run into someone who wants to know why the LM didn't need to be turned while it was on the surface.
I pointed out that the thermal environment on the moon is very different than in deep space, which elicited a rather skeptical response: "It's all just space!". I don't think he understood my explanation involving thermal (longwave) IR emissions.
I also said that my understanding is that the BBQ roll was primarily to protect the CM's heat shield, while the LM lacked a heat shield to protect and was well insulated with thermal blankets.
And I said that while LM could control its own temperature on the lunar surface by active cooling, this expended precious water and battery power. By rolling the whole stack on the way to the moon, the LM could be shut down and those consumables preserved for use on the moon. The LM still had a few heaters that were kept operating on CSM power on its way to the moon.
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Post by brotherofthemoon on Feb 18, 2010 20:23:21 GMT -4
Finally, I have an excuse to break out my copy of Virtual LM. Pages 194 and 195 feature some interesting 3D models depicting the ascent stage's "passive" thermal control system. For the most part, the crew cabin, thermal blanket, and micrometeorite shield never actually came into contact with one another. As shown in these diagrams, they were mounted on supports which kept it at least two inches from the structure. A simple, ingenious system - which explains why HBs can't seem to understand it!
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Post by PhantomWolf on Feb 18, 2010 21:33:04 GMT -4
we actually have something on Earth that works very much like the way the LM's passive thermal systems were set up. It's called a thermos (or vaccum) flask.
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Post by ka9q on Feb 20, 2010 13:17:08 GMT -4
Actually predicting the temperature of any spacecraft in a certain thermal environment requires a detailed analysis, usually involving a fairly complex thermal model running on a computer.
So does anybody happen to know how the quiescent LM behaves thermally:
1) in deep space with a fixed solar attitude, e.g., shining on the -Z (rear) side; 2) in deep space performing a slow continuous yaw about the X axis with the sun perpendicular to this axis; and 3) on the lunar surface in mid morning with the sun shining on the -Z and +X surfaces?
My understanding is that the LM structure was more or less able to take care of itself passively thanks to extensive thermal blanketing.
The RCS thrusters were a significant thermal problem. They had to be mounted on the LM where they could provide the necessary torque and cool themselves by radiation, and this could cause them to get quite cold and possibly misfire were they to remain out of sun in deep space for an extended time. So they were provided with electrical heaters.
The LM needed active cooling (water evaporation) primarily to reject waste heat from the systems, so this cooling was not needed when the systems were shut down.
Is this mostly correct?
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Post by fiveonit on Feb 20, 2010 22:46:01 GMT -4
While we're on the topic of the LM, perhaps someone could answer a question for me. I noticed that in many of the stills taken while in Lunar Orbit, the CM is below, in a lower orbit than the LM. Why would the LM ever need to be in a higher orbit once it separated from the CM?
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Post by JayUtah on Feb 22, 2010 2:06:50 GMT -4
It's higher at one end so that it can be lower at the other end and yet have the same period. The CSM and LM orbits were initially designed to be harmonic and to afford two rendezvous opportunities per rev.
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Post by fiveonit on Feb 22, 2010 20:59:52 GMT -4
It's higher at one end so that it can be lower at the other end and yet have the same period. The CSM and LM orbits were initially designed to be harmonic and to afford two rendezvous opportunities per rev. So if I understand you correctly, they both had elliptical orbits. Which makes senses to me, considering (as far as I know) there's no such thing as a perfect orbit. Since the 2 orbits did not overlap perfectly, this gave them a rendezvous opportunity at each point were the 2 orbits intersected. Am I close or way off base?
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Post by JayUtah on Feb 22, 2010 21:09:01 GMT -4
Yes, that's essentially it.
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Post by carpediem on Mar 2, 2010 20:28:15 GMT -4
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Post by ka9q on Mar 2, 2010 21:00:00 GMT -4
Tried to look at Svector's videos tonight and found the account was suspended. Wonder why? What's the usual reason, a DMCA complaint? Would be a shame to lose his stuff, he's a regular hoax debunker. Under the alias "rudbrps" he pulled a cute hoax on the hoaxers in which he superimposed himself in casual clothes at the edge of a surface scene from Apollo 16 and labeled it as "found footage" from a relative. At least one HB insists that the scene was real and svector/rudbrps is just trying to discredit it. :-)
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Post by ka9q on Mar 2, 2010 21:14:43 GMT -4
For the most part, the crew cabin, thermal blanket, and micrometeorite shield never actually came into contact with one another. This is to enhance micrometeoroid protection. When a particle hits the outer blanket it may not lose a lot of momentum but it fragments into a spray of little bits. The gap between the layers allows them to spread out before they hit the next layer, which can then stop them more easily as independent small particles. It's a Whipple Shield and an example of clever engineering that the HBers can't even begin to appreciate. Misapplying their earth-based intuition, all they see is a flimsy-looking device covered with foil. They can't begin to fathom how it could stop anything moving so fast. It just occurred to me that the Whipple shield is analogous to an entirely different mechanism in my own field, communications: concatenated coding. It's common to stack one error correcting code on top of another with an "interleaver" between them to spread out any uncorrected errors from one decoder before they reach the other. Many codes perform better when the errors are spread out in time instead of occurring in a burst, even when the average error rate is the same.
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Post by Data Cable on Mar 3, 2010 1:54:31 GMT -4
For the most part, the crew cabin, thermal blanket, and micrometeorite shield never actually came into contact with one another. This is to enhance micrometeoroid protection. Not to mention thermal insulation. The only direct conduction paths from inner hull to outer skin would be the standoffs themselves.
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Post by ka9q on Mar 3, 2010 2:38:11 GMT -4
Not to mention thermal insulation. The only direct conduction paths from inner hull to outer skin would be the standoffs themselves. Well yes, but any amount of separation in a vacuum would do that. You don't need the layers any farther apart than necessary to keep them from touching. They would still be radiatively coupled, which is why the facing layers are usually metalized. Most metals are highly reflective in the long IR as well as the visible spectrum, and objects near room temperature have the peak of their thermal blackbody curves in the long IR.
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Post by trebor on Mar 4, 2010 19:39:31 GMT -4
To go back to the topic of funny YouTube comments, here is one from a HB....
He then went on to claim that mass and weight are exactly the same thing, and that you lose mass when in a different gravitational field.
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Post by Ginnie on Mar 4, 2010 20:00:40 GMT -4
...hold on there - am I reading that right?
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