Author Topic: Skylab 3 Apollo CSM  (Read 10850 times)

Offline Launchpad911

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Skylab 3 Apollo CSM
« on: 11/13/2009 04:38 PM »
I was looking online today for photos of the Skylab 3 launch and also found this picture of the CSM docked to Skylab -



In the above photo, the command module is dull white rather than the typical silver/gold of the lunar type Apollo command module like below -



I know there must be someone here that can explain the difference in appearance. I thought all Apollo command modules had a reflective coating. Thanks for you help.
« Last Edit: 11/13/2009 04:39 PM by Launchpad911 »

Offline iontyre

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Re: Skylab 3 Apollo CSM
« Reply #1 on: 11/13/2009 04:41 PM »
I think you are seeing reflection off the Skylab itself, not the color of the CSM.

Offline Jorge

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Re: Skylab 3 Apollo CSM
« Reply #2 on: 11/13/2009 04:41 PM »
I was looking online today for photos of the Skylab 3 launch and also found this picture of the CSM docked to Skylab -



In the above photo, the command module is dull white rather than the typical silver/gold of the lunar type Apollo command module like below -



I know there must be someone here that can explain the difference in appearance. I thought all Apollo command modules had a reflective coating. Thanks for you help.

All Skylab and ASTP CMs were as shown in the picture. The different coating is for thermal.
JRF

Offline Launchpad911

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Re: Skylab 3 Apollo CSM
« Reply #3 on: 11/13/2009 05:05 PM »
Thanks for the quick replies. A picture of the ASTP CM after splashdown shows it had a mirror coating like a lunar Apollo CM. I thought thermal protection was the reason they had this mirror coating. Would a mirror coating provide more radiation protection since the lunar Apollos travelled outside the Van Allen belt?


Offline kevin-rf

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Re: Skylab 3 Apollo CSM
« Reply #4 on: 11/13/2009 06:03 PM »
I think it was for thermal control while attached to skylab, half the CM was painted. You can sort of see the silver side on the top edge in your photo.
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Offline Launchpad911

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Re: Skylab 3 Apollo CSM
« Reply #5 on: 11/13/2009 06:55 PM »
I think it was for thermal control while attached to skylab, half the CM was painted. You can sort of see the silver side on the top edge in your photo.

I think you are right. I found to images of the CM on display and you can see definite delineating lines. Is this image you can see a line running through the right side docking window.



This image is very large so I will only post the link -

http://historicspacecraft.com/Photos/Apollo/CM-118_NASM_2008_RK_2.jpg

You can see the line running up the left side. The white are is the same shown in my original photo. It is strange the CM didn't have a uniform application of reflective material. Thanks for noticing that, Kevin.


« Last Edit: 11/13/2009 06:57 PM by Launchpad911 »

Offline kevin-rf

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Re: Skylab 3 Apollo CSM
« Reply #6 on: 11/13/2009 07:14 PM »

I vaguely remember it being discussed in the past on one of the billions and billions of nsf space flight threads...
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Offline Jim

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Re: Skylab 3 Apollo CSM
« Reply #7 on: 11/13/2009 07:41 PM »
It is strange the CM didn't have a uniform application of reflective material.


It isn't strange.  Skylab CSM's had to be modified because 95% of the time, the same side always faced the sun while docked to Skylab, unlike during Apollo missions where they could perform the BBQ roll for thermal condition.  The white is passive thermal control and reflects the solar heat.  There were other mods like extra heaters on the opposite side of the CSM, since it would not be in the sun

Offline Jim

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Re: Skylab 3 Apollo CSM
« Reply #8 on: 11/13/2009 07:41 PM »
Would a mirror coating provide more radiation protection since the lunar Apollos travelled outside the Van Allen belt?


Nothing to do with radiation, see above

Offline koennecke

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Re: Skylab 3 Apollo CSM
« Reply #9 on: 11/13/2009 11:12 PM »

http://images.jsc.nasa.gov/luceneweb/fullimage.jsp?searchpage=true&selections=SL3&browsepage=Go&hitsperpage=100&pageno=2&photoId=S73-36435
A recovered CM-117 aboard USS New Orleans. The two distinct surfaces can be seen. Why the surgical masks? Was it a question of immune supression during extended stays in orbit?
« Last Edit: 11/13/2009 11:15 PM by koennecke »
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Offline Jim

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Re: Skylab 3 Apollo CSM
« Reply #10 on: 11/14/2009 12:07 PM »
Why the surgical masks? Was it a question of immune supression during extended stays in orbit?

Yes

Offline Hoonte

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Re: Skylab 3 Apollo CSM
« Reply #11 on: 11/14/2009 05:00 PM »

Offline Skylon

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Re: Skylab 3 Apollo CSM
« Reply #12 on: 11/15/2009 04:34 PM »
Thanks for the quick replies. A picture of the ASTP CM after splashdown shows it had a mirror coating like a lunar Apollo CM. I thought thermal protection was the reason they had this mirror coating. Would a mirror coating provide more radiation protection since the lunar Apollos travelled outside the Van Allen belt?



The ASTP CM was originally slated for a lunar mission (Apollo 15 before it was made a J-mission).

Offline Comga

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Re: Skylab 3 Apollo CSM
« Reply #13 on: 11/18/2009 04:52 AM »
It is strange the CM didn't have a uniform application of reflective material.

It isn't strange.  Skylab CSM's had to be modified because 95% of the time, the same side always faced the sun while docked to Skylab, unlike during Apollo missions where they could perform the BBQ roll for thermal condition.  The white is passive thermal control and reflects the solar heat.  There were other mods like extra heaters on the opposite side of the CSM, since it would not be in the sun

Isn't it a matter of emissivity? Both the metallic and white surfaces reflect the majority of the solar flux, which is visible and Near IR light, but the white paint can have a higher emissivity, essentially absorptivity in reverse, out in the thermal infrared.  Isn't that the way it radiates and "rejects" the heat better than a "silvered" surface which has very low emissivity?  I know they use white paint for that reason on satellite thermal radiators.
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Offline Lars_J

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Re: Skylab 3 Apollo CSM
« Reply #14 on: 11/18/2009 10:58 PM »
It does seem a bit strange still... A perfect mirror and a perfectly white surface reflect just as much light/flux/thermal radiation. The only difference is the pattern of the reflection. (reflected back in one direction versus spread out in all directions)

But perhaps the white paint had other properties that made it useful.
« Last Edit: 11/18/2009 10:58 PM by Lars_J »

Offline MKremer

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Re: Skylab 3 Apollo CSM
« Reply #15 on: 11/18/2009 11:24 PM »
It does seem a bit strange still... A perfect mirror and a perfectly white surface reflect just as much light/flux/thermal radiation. The only difference is the pattern of the reflection. (reflected back in one direction versus spread out in all directions)

But perhaps the white paint had other properties that made it useful.

Right. There's a big difference in thermal characteristics between plain white enamel paint and white thermal coat 'paint'.

Offline Comga

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Re: Skylab 3 Apollo CSM
« Reply #16 on: 11/18/2009 11:39 PM »
It does seem a bit strange still... A perfect mirror and a perfectly white surface reflect just as much light/flux/thermal radiation. The only difference is the pattern of the reflection. (reflected back in one direction versus spread out in all directions)

But perhaps the white paint had other properties that made it useful.

Right. There's a big difference in thermal characteristics between plain white enamel paint and white thermal coat 'paint'.

The photos are so wonderful that I was just going to enjoy them and not going to comment on this detail, but as it is being discussed...

The other property is emmisivity, the ability to radiate energy in the form of infrared radiation.

A shiny metailic plate will reflect visible light, preventing heat build-up from sinlight.  But it would also reflect infrared light, like the 10 micron stuff we give off at 310 K = 98.6 F.  To obey the laws of conservation of energy and thermodynamics, if it can't absorb IR light, it can't radiate it either.  Otherwise you get a one-way "energy valve" to power your perpetual motion machine.   :-P

So if you put an insulated  metal plate in the Sun, it will heat up slowly, but it will get very hot.

If you cover a plate with just the right white paint, one that reflects visible light that we see but absorbs far infrared light we can't see, it CAN radiate or emit the heat energy.  That's called "high emissivity" and is the thermal property MKremmer is refering to.

It would also heats up slowly, because it is scattering the visible sunlight which is most of the solar energy.  However, it also radiates its own thermal energy.  It will heat up slowly, but soon reach an equilbrium without getting very hot.

Does that make sense?
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Offline Herb Schaltegger

Re: Skylab 3 Apollo CSM
« Reply #17 on: 11/20/2009 02:00 PM »
It does seem a bit strange still... A perfect mirror and a perfectly white surface reflect just as much light/flux/thermal radiation. The only difference is the pattern of the reflection. (reflected back in one direction versus spread out in all directions)

But perhaps the white paint had other properties that made it useful.

Emissivity.
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