BA if this is too long...let me know and I'll edit it down more...

my comments are in italics.

SAMU says:
About your message.

Quote:

"Actually, I find the rebuttals of more interest."

Which one was your favorite?

SAMU

These are just some of them and they are cut up and out of order.

JayUtah:

First, albedo. Geometric albedo concerns only zero-phase diffuse reflection. It does not consider specular reflections, which in many substances accounts for a vastly different visual phenomenon. The moon's albedo is measured as low as 0.07 and as high as 0.12, meaning it diffusely reflects between 7% and 12% of the light it receives back toward the source of the light. The earth's albedo is somewhere in the 0.30 range, considerably brighter than the moon. In fact, when you see pictures of both the earth and the moon taken by outbound interplanetary spacecraft, you have to artificially brighten the moon because the correct exposure for the earth leaves the moon a rather unimpressive dark brown. This I didn't know.

The moon appears bright from earth because it's a the brightest object in an otherwise lightless environment. Look at a candle in daylight, then look at one in an otherwise dark room. This I understood

Second, asphalt. Or more properly, "bitumin asphalt concrete". "Concrete" is, in the general engineering sense, anything composed of an aggregate and a cement. In what we commonly call concrete, the aggregate is sand and gravel and the cement is Portland cement or other such compound. "Asphalt" (bitumin) is the cement in the asphalt concrete used in roadway construction. The aggregate is usually pea gravel. The bitumin asphalt holds the aggregate together in the same way Portland cement holds the aggregate together in concrete. This I've had some experience with - briefly having worked in the aggregates industry (a company I worked for temporarily recycled asphalt).

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The thermal behavior of an object in space under solar radiation is directly affected most strongly by the reflectivity of that object. The Apollo command module was covered in aluminized Kapton insulation. The lunar module was covered in several blankets of aluminized Mylar insulation. The geometric albedo of these materials as applied to the spacecraft is in the 0.50 neighborhood. (It differs from the values for aluminum because the Kapton and Mylar sides were outboard.) I didn't know the material used in the lunar module

The Bad Astronomer:

I have pictures of asphalt I took that make it look bright white. How things look depends on many things, not the least of which is how you expose the film. There are pictures of the Moon's surface making it look pitch black, too. Worse, the illumination of the lunar surface depends on the angle of the sunlight with respect to the camera as well. Understand over/under exposure of film and it's effects on the appearance of surfaces.

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David Simmons

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One more time. Aluminum reflects anywhere from 85% to 91%(depending upon surface treatment such as anodizing, roughening, etc.) of the light that falls on it. Solar energy at earth orbit is 0.033 cal/sec/cm^2. This means that about 0.0043 cal/sec/cm^2, as an assumed overall average, actually enters the aluminum. If the aluminum radiates as a black body the temperature of the skin would be about -36 deg C, or about -32 deg F. The astronauts would rapidly freeze to death. Interesting info here and I can confirm it too.

And, by the way, that heat input is only for those square cms. that are at right angles to the suns rays. Most parts of the capsule exterior would be at some grazing angle less than 90 deg and the heat input to those parts would go way down.I hadn't considered this originally myself - but referring back to JayUtah's information - this is presented there also.

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Karl:

I don't think any of the titanium was exposed so it's not relevant. Metal tends to run hot, (like the polished aluminum). White paint tends to run cold, it it used for radiators. Epoxy white paint Absorptance = .2 Emittance = .85, Acrylic white paint Absoptance = .22 Emittance = .88

The exposed surface of the LM and CM were multilayer thermal blankets.

From another post:

As an interesting part of the side issue, a polished aluminum mirror put in orbit to perform the function you are describing would run very hot, the a/e values for that material are listed as: absorptance = .35 and emittance = .04 for and a/e of 8.75

A 'mirror' made of black paint would run much cooler: absorptance = .97 emittance = .91

If you really want it to run cold, make your mirror out of Optical Solar Reflectors ( silvered quartz mirrors with Teflon): absorptance = .08 emittance = .81

It's amazing how intutition fails totally when dealing with thermal optical properties.

Information I didn't have, but that can be confirmed...

K. Hovis:

snipped... The LM's were made primarily from Titanium, the outer skins being .015" thick in many places. Titanium loses 10% of its strength and will enlongate about 10% of a part's length when exposed to 200 deg. F heating for 1/2 hr. (Check MIL-HNDBK-5F for 6Al-4V Ti).Milspecs I understand...and I know where to check the info

Donnie B.:

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The main question is, if an Apollo spacecraft lost nearly all electrical power, would the cabin warm up or cool down?

Your own evidence shows that the designers were coping with a major heat buildup problem(under normal conditions) -- so much so that they had to provide lots of active cooling. The issue becomes, what is the source of that heat? We know of three possibilities: solar radiation, the astronauts' metabolisms, and the onboard electronic equipment. Which was the main contributor?

If it was the electronics, your claim falls apart, because all the CM systems were shut down, and the LM systems were running at a minimum level (and still being actively cooled, I might add -- you can't use a computer as a space heater without causing it to fail in both capacities).

OK, so how do we determine where the heat came from? We can discount the astronauts themselves. Their body heat wasn't nearly enough to require all that refrigeration. So was it the sun, or the electronics? I say that the presence of the radiators proves that it was the latter.

Remember, weight is critical on any space mission, and the lunar missions especially so. Refrigeration systems are heavy, and the more heat they have to dissipate, the heavier they get. So a spacecraft designer is going to do everything in his power to reduce the amount of heat that has to be removed.

But an electrical or electronic system can only get so efficient (given a particular era's technology). This was in the infancy of mircocircuits, and even a modern computer puts out quite a bit of heat. So for a given roster of electrical gear, there would be an irreducible heat budget.

But solar gain is something you can do something about, and it's not only easy to do but costs nothing in weight. That's to make the spacecraft as highly reflective as possible, reducing the solar gain so as to make the cooling system's job that much easier. A shiny surface doesn't weigh any more than a dark one -- maybe less.

In summary:
- Apollo had active cooling systems.
- So, Apollo had to get rid of excess heat.
- So, Apollo would have been designed to absorb as little solar heat as possible.
- So, since it still needed radiators even though it was reflective, the heat source was something else.
- So, the heat source was internal electrical equipment.
- The electrical equipment was nearly all turned off after the explosion on 13.
- Therefore, the cabin got cold.

I've said all I care to say on this topic. Have a nice, paranoia-filled life, SAMU.

Those old electronics ran hot. They still have cooling problems with electronics. That was one of the assumed problems with exceeding a 586 processor - cooling it.

JayUtah

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Quote:
B.A.:The Moon is not a specular reflector

True, but asphalt is. I wasn't trying to describe the moon as much as I was trying to point out that geometric albedo is a poor quantification of the total lighting properties of a surface. Something like asphalt with a "low" albedo can actually reflect enough light in the specular sense (not measured by albedo) to impair vision. The glare off the asphalt roadways here in Utah is quite striking.

You mention the moon's emphasis on zero-phase lighting. That's correct, visually verifiable from earth, and quite evident in the Apollo lunar surface photographs. Again, geometric albedo does not account for these "special" lighting effects, hence it is a poor quantification for the lighting properties of the lunar surface.

Quote:
SAMU:You want to talk metals? Now you're talking my bussines.

The skill of cutting metal to a pattern given to you by someone else is not equivalent to the skill of determining those patterns. That happens to be my busines. When you cut tailcones or wing spars or what have you, you're simply following the instructions given to you by people like me who work out the designs for you. I've heard this many times when refering to engineers. That the person actually doing the job and working with the material knows more - that's simply not the case - as for understanding the all the considerations that go into the best material - I'll leave that to the engineers. I'll just constrain my *****es to not enough room to actually perform necessary maintenance when they do the layout design for a peice of equipment.

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The arguments you offer in favor of your assertions demonstrate that you don't understand thermodynamics. A proper understanding of thermodynamics is necessary to the claims you're making. Not only do you seem rather ignorant on the subject of thermodynamics, you seem especially antagonistic to those who are trying to educate you. I enjoyed the discussions regarding thermodynamics at the last job I had. This is sounding familiar, and reinforcing that which I was learning about there.

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Quote:
SAMU: there is no legitimatly supported theory as to why Apollo 13 got cold when enormous expense is invested in throwing a cooling system that is designed to manage deadly heat up there and it "has to be turned off".

What do you mean by "legitimately supported"? The thermodynamics numbers others have posted seem correct to me. The only quantitative arguments you have made don't constitute valid thermodynamics.

The cooling of the command module has been explained to you as plainly as it can be. The primary source of heat on the Apollo spacecraft was the electronic equipment. The heat production of the astronauts and that absorbed from the sun is very small in comparison. If you run the electronic equipment you must also run the cooling units. If you turn off the electronic equipment you do not need the cooling units. You must either run both or neither.

Without that electronic equipment, the only sources of heat are the astronauts themselves and the radiant heat absorbed from the sun. You've been shown the black-body figures for an object in that situation, which you have sidestepped.

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Christopher Ferro

Jay,

Well, I have come across one bit of albedo stuff online that talks about how difficult it is to compare albedos on Earth with that of objects in space.

http://www.roboticobservatory.com/je...ech/albedo.htm

I will note that comparing the albedo of grass to that of lunar surface material as this author does, is not a "fair" comparison either. Grass looks green to us mostly because chlorophyll absorbs most of the red and blue wavelengths it receives. The brightness of grass is also due to our eyes/brains manipulating the contrast. The problem there is that one can measure albedo in various wavelengths.

Here is a report from an instrument called GOME:

http://www.sron.nl/divisions/eos/gome_moon.html

It shows the albedo falling withing the 6-12% zone, on average, with what seems to be a slight, linear increase in albedo from Near UV to Near IR wavelengths.

CJSF

Great links - but JayUtah got to say that first. Something else to add...

JayUtah

Christopher, excellent material!

I especially like Medkeff's straightforward and comprehensive examination of the geometry of the lunar regolith and its effect on light. me too. Not only does this dispel the incorrect use of albedo as a practical measure of lighting properties, it gives the beginner something of a foothold on what is otherwise an obscure bit of science. Well I can say I understood a good portion of what was said here.

It's difficult to convey in purely textual form the geometrical nature of the behavior of reflecting light. A few years ago I came across a visual representation scheme for incident and reflected light used by computer graphics people, namely Cook, Torrance, and Sparrow. It represents the intensity of reflected light in any direction by a vector along that direction whose magnitude is proportional to the reflection intensity. The set of all such vectors form a surface composed of the vector heads, and which conveys for some incident light direction the total character of the reflected light. Would you believe this...in computer animation we use specular, blinn, phonng, and someother type of light reflectivity - and we can layer the info - hey maybe I can create an accurate moon now! Not likely - but I can try.

JayUtah

Quote:
BA and JayUtah, you two mention "specular reflector" vs. the albedo. I do not understand what you mean. Could you please explain?

The various definitions of albedo do not generally account for any lighting conditions other than Lambert surfaces -- those which reflect light uniformly in all directions regardless of incident light angle. This I didn't know.

In contrast to the Lambertian surfaces we find materials which reflect greater amounts of light in a particular direction congruent to the incident light angle. We term this "specular reflection". Roadway glare is one example of it.Yup! need this for the computer animation stuff - but I went about it through trial and error - now I have info that I can actually plug into the system that it can use - and hopefully *look* correct. Easier than playing and rendering for 4 or 5 hours.

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_________________
Time crumbles things; everything grows old under the power of Time and is forgotten through the lapse of Time.
~Aristotle

<font size=-1>[ This Message was edited by: Trish on 2001-11-14 04:55 ]</font>