Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V08/V8_236.TXT

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From ota Sat May 28 03:04:37 1988
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Date: Sat, 28 May 88 03:04:22 PDT
From: Ted Anderson <ota>
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Subject: SPACE Digest V8 #236

SPACE Digest                                      Volume 8 : Issue 236

Today's Topics:
               Name change vote
              Re: Hawaiian launch sites
              Re: Hawaiian launch sites
             Re: How hot is it in space?
             Re: How hot is it in space?
             Re: How hot is it in space?
             Re: How hot is it in space?
             Re: How hot is it in space?
             Technology Transfer Worries?
          Mir watch predictions and orbital elements
           Re: Mir watch predictions and orbital e
----------------------------------------------------------------------

Date: Mon, 9 May 1988 13:19-EDT
From: [e-mail]
To: "/usr/amon/Email/Email.L5" <[e-mail]>
Subject: Name change vote

The results are official. Ballots were counted over the weekend by Gary
Oleson and Terry Dawson:

National Space Society:        3388        64%
Space Frontier Society:        1830        34%
Blank and write-in:          64         1%


The numbers I'm giving might possibly be off by a few since I got them
from Gary at his office and he quoted them from memory. Nonetheless,
the results are rather overwhelmingly in favor of NSS. For all those
who took voted, regardless of your choice, I thank you for
participating in the democratic process. I personally may not agree
with the choice, but the will of the majority has been spoken.

                Welcome to the National Space Society.
                Dale Amon
                NSS Board of Directors

------------------------------

Date: 7 May 88 22:16:15 GMT
From: cfa![e-mail]  (Steve Willner)
Subject: Re: Hawaiian launch sites

[Apparently this article failed to go out earlier.  If it did go out, I
apologize for sending it twice.]

>From article <[e-mail]>, by [e-mail] (Eugene N. Miya):
> Ach!  You guys have such a lack of sensitivity!  A great way to wreck
> one of the best optical observing sites in the world.  Okay, SPACE at
> all costs.

You refer no doubt to Mauna Kea, from which I have just returned.  It is
indeed one of the world's best observing sites.  But how wreck?  The
work lights would be behind Mauna Loa and below the clouds.  Launches
would only briefly illuminate the south.  And if ever there comes a time
when there are many launches per night, some of them will be carrying
telescopes.

Steve Willner            Phone [phone]         Bitnet:   willner@cfa
60 Garden St.            FTS:      830-7123           UUCP:   willner@cfa
Cambridge, MA 02138 USA                 Internet: [e-mail]

------------------------------

Date: 12 May 88 15:10:49 GMT
From: mcvax!ukc!its63b![e-mail]  (ERCF08 Bob Gray)
Subject: Re: Hawaiian launch sites

In article <[e-mail]> [e-mail] (Peter Scott) writes:
> ... Does anyone know where Ariane
>is built and how it is shipped to Kourou?

As I haven't seen any other replies...

Arianne is built at the Aerospatiale works in France,

The first and second stages are taken my sea to Kourou.
The third stage and payload are taken by air.
    Bob.

------------------------------

Date: 4 May 88 18:08:30 GMT
From: [e-mail]  (Joe Beckenbach)
Subject: Re: How hot is it in space?

In article <[e-mail]> [e-mail] (Thomas Hacker, ACM) writes:
>>of about 290 K (no surprise). Surprisingly (to me, anyway) a polished
>>aluminium body will be much hotter (it absorbs less sunlight, but
>>radiates far less).
>
>Why would a polished surface be much hotter if it is not absorbing any
>energy (if it reflects 100% of the incoming radiation across the whole
>spectrum), and it is (I assume) radiating energy due to heat radiation
>(usually called "blackbody" radiation)? Planck's law doesn't have a
>term within it that makes the intensity of the radiation emitted a
>function of the reflectivity of the surface.

>Thomas J. Hacker ([e-mail])

    Because aluminum and other metals, though they absorb little in
the way of EM radiation, they can radiate it much more slowly than they
can receive it. Most metals [that I've come in contact with.. OUCH! :-)]
reflect visible light well and infrared less well. They can't reradiate
at all quickly though! That is why metals are hot in sunlight on the
earth, and after an hour's drive in the country you can't stand barefoot
on the hood of your car without risking severe burns for about fifteen
minutes.
    The reflectivity of the body is not involved in Planck's Law,
true; the problem is that no material reflects evenly over the entire
spectrum.  Planck's Law describes only what goes out, not how it got in.
And no material is actually a black body- I don't know what comes
closest.
    So to design using a material knowing it will both radiate and
absorb, the problem is to balance the input and output energy. If a hunk
of radiator will be in sun 50% of the time and exposed to black space
50% of the time, I need to know the ratio of reradiation to absorbtion.
If it absorbs faster, I get more energy than I can reradiate later in
the radiator-- instead of cooling I get heating. Oops. Ratio of 1.0000..
is not a help either: the energy taken in matches the energy reradiated,
and I can't use it to cool my craft. Only when the _net_ reradiation is
greater than the _net_ absorbtion will my radiator be useful. Polishing
normally ups the reflectivity, thus lowering the absorption rate;
conventional wisdom states that polishing does nothing to the
reradiation rate from Planck's Law.

Joe Beckenbach    CS BS ??            -- I'D RATHER BE ORBITING

------------------------------

Date: 7 May 88 22:22:44 GMT
From: cfa![e-mail]  (Steve Willner)
Subject: Re: How hot is it in space?

[Apparently this failed to go out earlier.  If it did go out, I
apologize for sending it twice.]

In article <[e-mail]>, [e-mail] (Thomas Hacker) writes:
> Why would a polished surface be much hotter if it is not absorbing any
> energy (if it reflects 100% of the incoming radiation across the whole
> spectrum),

Nothing, except possibly a superconductor, is a perfect reflector.
Polished aluminum, for example, reflects only about 93% of visible
light.

> and it is (I assume) radiating energy due to heat radiation (usually
> called "blackbody" radiation)?

If it can't absorb, it can't radiate.  Look up "Kirchhoff's Law."

> Planck's law doesn't have a term within it that makes the intensity of
> the radiation emitted a function of the reflectivity of the surface.

Planck's law contains a _factor_ called "emissivity".  Radiation emitted
or absorbed is proportional to this factor.  In general, emissivity is a
function of wavelength.  For aluminum, the visible emissivity is about
7% (as noted above), while the infrared emissivity is about 2%.  Thus an
aluminum sheet will be hotter than a blackbody when illuminated by
sunlight.

(I suppose one could adopt a definition of "Planck's Law" that omits the
emissivity factor and thus applies only to perfect blackbodies, but
that's a matter of semantics, not physics.  One certainly has to include
emissivity in calculating thermal emission from real objects.)

Steve Willner            Phone [phone]         Bitnet:   willner@cfa
60 Garden St.            FTS:      830-7123           UUCP:   willner@cfa
Cambridge, MA 02138 USA                 Internet: [e-mail]

------------------------------

Date: 9 May 88 22:28:51 GMT
From: ddsw1!igloo![e-mail]  (Bronis Vidugiris)
Subject: Re: How hot is it in space?

I don't know how to describe the actual charachteristics of polished
aluminum exactly.  I do know, however, that it does NOT reflect 100% of
the incoming radiation across the spectrum.  I believe the region where
it starts to absorb significantly is in the infra-red, but don't quote
me.

I also know that blackbody radiation is a special case which
DELIBERATELY excludes the properties of the surface from the radiation.
A blackbody is can be made by making a very small pinhole in a hot
cavity, as I recall...

Bronis Vidugiris
igloo!bhv@ddsw1

------------------------------

Date: 16 May 88 22:24:41 GMT
From: netsys!nucleus![e-mail]  (Thomas Hacker)
Subject: Re: How hot is it in space?

In article <[e-mail]> [e-mail] (Bronis Vidugiris) writes:
>exactly.  I do know, however, that it does NOT reflect 100% of the incoming
>radiation across the spectrum.  I believe the region where it starts to
>absorb significantly is in the infra-red, but don't quote me.

   Thank you, I wasn't aware of this.

>I also know that blackbody radiation is a special case which
>DELIBERATELY excludes the properties of the surface from the radiation.
>A blackbody is can be made by making a very small pinhole in a hot
>cavity, as I recall...

   Quote from "Modern Physics"
   Paul Tipler
   Oakland University
   Worth Publishing 1977
   page 102

   "When radiation falls on an opaque body, part of it is reflected and
the rest absorbed.  Light-colored bodies reflect most of the radiation
incident upon them, whereas dark bodies absorb most of it.  If an opaque
body is in thermal equillibrium with its surroundings, it must emit and
absorb radiation at the same rate...."
   "...The radiation emitted under these circumstances is called thermal
radiation....As a body is heated the quantity of thermal radiation
emitted increases, and the energy radiated tends to shorter and shorter
wavelengths..."
   "...A body that absorbs all radiation incident on it is called an
_ideal blackbody_."

   An example a thermal radiator you see in everyday life is an
incandescent light bulb.  It gets very hot due to resistive heating and
thus gives off thermal radiation.
   Thus, I should have said "thermal radiation" instead of "blackbody
radiation", but the people around here call it blackbody radiation.

   Someone told me that the interior of the cargo bay doors of the space
shuttle are covered with a polished metal to dissipate heat.  Is this
true?  How does it work?

Thomas J. Hacker            ...!uunet!umix!nucleus!hacker ([e-mail])
Physics/CS Undergrad
Oakland University                 "Physics is the poetry of nature."
Rochester, MI 48063

------------------------------

Date: 18 May 88 15:39:24 GMT
From: attcan!utzoo![e-mail]  (Henry Spencer)
Subject: Re: How hot is it in space?

> Someone told me that the interior of the cargo bay doors of the space
> shuttle are covered with a polished metal to dissipate heat.  Is this
> true?  How does it work?

Someone's misunderstood.  The shuttle's cooling radiators are indeed
located on the inside of the cargo bay doors -- that's why the doors
must be opened fairly promptly on reaching orbit, or else the shuttle
has to come down immediately -- but they are active devices, with
circulating fluid, pumps, electronic control, etc.

 Henry Spencer @ U of Toronto Zoology
{ihnp4,decvax,uunet!mnetor}!utzoo!henry

------------------------------

Date: 5 May 88 20:11:29 GMT
From: [e-mail]  (Eric William Tilenius)
Subject: Technology Transfer Worries?

In article <[e-mail]>, [e-mail] (Mike Smithwick) writes:
>"Wouldn't something like this cause problems in the area of stealing
>secrets???"
>
>Carl : "Well, yes, the Soviets would have to worry about us, seeing
>that they are so far ahead in both manned and planetary space
>exploration" (not quite an exact quote, but you get the idea).
>
>This is not to criticize the concept of the mission, so don't start
>another flame.war about that. Just Carl should learn to think before he
>speaks.

I think his point was not what you quoted.  He was trying to say that
there wasn't any real danger in such a peaceful, cooerative space
exploration mission, of technology transfer.

Rather, the Russians might have to SLOW the pace of their Mars
expeditions to make room for us, since they are ahead in scheduling such
missions.

(As an aside, I agree that technology transfer isn't a big issue...
don't you think the Soviets can find out what NASA is up to?  And this
is peaceful technology as well, most of which they do themselves.)

Carl meant to turn the question around, just to make people think... If
the Soviets keep up the current pace, they may have to worry about us
after all.

He wasn't stating it as a set fact (the WILL have to worry about us),
but rather to say that we are on comparible terms, except they have a
more ambitious program at present.

------------------------------

Date: 5 May 88 21:22:37 GMT
From: mtunx!lzaz!lznv![e-mail]  (Paul S. R. Chisholm)
Subject: Mir watch predictions and orbital elements

I just had an interesting chat with a friend about Mir watches and
predictions.  He gets orbital elements every five days, and is using
Woodcock's prediction software to calculate the timing and position of
good, observable passes.  He had some interesting comments.

First of all, his predictions have been late.  That is, Mir has been
showing up sooner than he would expect.  Before everyone jumps on
Woodcock's software, my friend did some thinking and is now suspicious
of NASA's elements!  The actual orbital decay is roughly twice the drag
listed in the elements.  (He quoted both; I dunno the numbers, but the
units were orbits/day, I think.  I just looked at T. S. Kelso's latest
posting, and didn't see anything familiar.  Then again, I haven't played
with orbital mechanics in nearly a decade, and never managed to get my
hands dirty with real objects and numbers.)

Anyway, he's going to play with the numbers: make the predictions twice,
once with NASA's elements, once again by adding a fudge factor of two to
the drag.  If he gets better predictions the second way, I'll let you
know.

Second, Mir was apparently boosted fifteen miles recently.  He'd heard
that Mir would adjust course "fairly often", and assumed this was
relative to geosynchronous satellite station keeping (about every three
weeks).  Nope; every four months is closer to it for Mir.

Third, he says there haven't been *any* observations in a while, not
even marginal ones.  This doesn't sound like a prediction problem; his
elements are never more than five days old, and he *has* gotten fairly
good predictions before.  This may mean something, but I dunno what.

-Paul S. R. Chisholm, {ihnp4,cbosgd,allegra,rutgers}!mtune!lznv!psc
AT&T Mail !psrchisholm, Internet [e-mail]
Neither my friend nor I are speaking for our employers.

------------------------------

Date: 7 May 88 17:28:00 GMT
From: [e-mail]
Subject: Re: Mir watch predictions and orbital e


/* Written  4:22 pm  May  5, 1988 by [e-mail] in uiucdcsm:sci.space */
First of all, his predictions have been late.  That is, Mir has been
  . . .
/* End of text from uiucdcsm:sci.space */

The NASA figure is off by a factor of two; this is intentional.  If you
use the NASA third derivatives of the mean anomaly, you'll find they're
off by a factor of 6.  They're actually the coefficients of a Taylor
series for the mean anomaly, and not the derivatives themselves.

I suspect you're right about Gordon's program.  I'll speak to him about
it at the Denver conference.

------------------------------

End of SPACE Digest V8 #236
*******************