Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V11_3/V11_387.TXT

Internet Message Format | 1991-07-08 | 20KB

Return-path: <[e-mail]>
X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/[e-mail] (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests)
          ID </afs/andrew.cmu.edu/usr1/ota/Mailbox/YaGZEN:00VcJ0IZU4j>;
          Fri, 11 May 90 01:56:42 -0400 (EDT)
Message-ID: <[e-mail]>
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Fri, 11 May 90 01:56:11 -0400 (EDT)
Subject: SPACE Digest V11 #387

SPACE Digest                                     Volume 11 : Issue 387

Today's Topics:
          Re: Manned mission to Venus (long)
          Venus and Mars and Asteroids O MY!
             Re: Re: Dyson spheres (long)
              Re: SPACE Digest V11 #344
    Re: Terraforming Venus (was: Manned mission to Venus)
            Re: Terraforming Venus
           Re: Voyager Confirms Relativity
        Re: A Non-military economy possibility
----------------------------------------------------------------------

Date: 10 May 90 15:48:30 GMT
From: usc!zaphod.mps.ohio-state.edu!uwm.edu!mailrus!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Manned mission to Venus (long)

In article <[e-mail]> [e-mail] (John Roberts) writes:
>You also seem to assume you would get windows. Of all the places in the
>solar system humans might conceivably go in the next 100 years, Venus is the
>least likely to have windows. Whatever is chosen for window material must
>withstand extreme pressure *plus* high temperature *plus* high temperature
>differential, must resist chemical attack, and must serve as an effective
>thermal insulator...   (Does anybody know what
>the Soviet landers used for windows?)

Not sure about the Soviet landers, but the big Pioneer Venus descent probe
used a diamond window for one of its instruments.  (Hughes got a rebate on
the import duty for the diamond after pointing out to US Customs that it
had been exported again!)
--
Life is too short to spend    |     Henry Spencer at U of Toronto Zoology
debugging Intel parts. -Van J.| uunet!attcan!utzoo!henry [e-mail]

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

Date: 10 May 90 19:40:33 GMT
From: zaphod.mps.ohio-state.edu!samsung!rex!rouge![e-mail]  (Fraering Philip)
Subject: Venus and Mars and Asteroids O MY!

This posting will, like the previous one, cover several topics:

1. Incomprehensibility of space:

Mark S. was talking about the space shuttle system, and why the liquid
hydrogen motors were both extremely complex and unsafe. I would like to
state that although the turbines on the SSME are very complex, they are not
much more complex than the most advanced jet engines in use today. The
problems with the SSME's are not due to the fact that they were liquid
hydrogen fuelled, but that our favorite bureaucracy has made them much
more complex and advanced than an engine should be (see all the recent
postings about the Six Blind Men and the Shuttle RFP...:-)

In fact, the most unsafe part of the shuttle was and is the SRB's. Without
their vibration loads, the SSME's would be much more reusable than they are
now. The shuttle would have exploded or crashed if it were fuelled with
 hydrogen, methane, gasoline, or old tires when the flame from the SRB
joint was held against the External Tank. Most designs for shuttle
replacements I have seen use Liquid Hydrogen but no solids (for safety as
well as economic reasons.)

2. About a Venus Base being a pleasant place to live:

Well, if you recreated an earthlike enviornment inside the giant bathyscape,
it would be a pleasant place to live. Of course, so would New Iberia.
Actually, as someone else has posted, you could do this anywhere. Would it
be worth it?

3. About space colonies and industrialization:

Hell, I can't think of any other way to power (and maybe even feed) the third
world. SPS would be better than burning the Rain Forests for a couple more
acres of fertile ground (which will remain so for only a year or two anyway).

4. About Carl Sagan: Surely he is being misquoted. He would be insane to
want to save the lifeless hunks of rocks which are the asteroids from the
chance to be used as resources to save the biosphere of the earth and to
save them from the awful fate of terraforming or being used to create
space colonies.

Mark S. also questions the ability of Space Industrialization to make
a difference in how we live here, saying the military will eat all of the
benefits and nothing here will change.

I severely disagree with this. Solar Power sattelites could provide a
cheap source of renewable energy indefinately. Asteroid mines could
provide us with metals without destroying biosphere. It would be exporting
our problems, but wouldn't it be prudent to export them to somewhere where
there is _no_ life whatsoever?

Given the several tens of thousands of asteroids out there, there are more
than enough for us to supply ourselves with metals well into the fourth
millenium, build space colonies, and still have enough left over for
Dr. Sagan to find out the ultimate Answer to Life, the Universe, and
Everything. (42!).

Finally, I would like to comment on Space Program Drivers. Mark's program
would be focused on spectacle and the achivement of very hard tasks so
that a few people could explore Venus.

It is also elitist as hell.

One of the main problems with the U.S. space program has been that it
contains so many programs, such as Hubble, the Neptune Probes, etc. that
cater mostly to pure scientists that it seems to be a vehicle mainly
for the studies of those _high priesthood_ projects of finding the
origin of the universe, what was God thinking when he did it, and other
such things.

The public wants very little part of this. They want to see benefits and
also a way for ordinary people to go into space, work there, and see space
exploration make a difference in the life of the people on this planet.

Space Industrialization can do this.

If we make the program mainly a spectator sport, it will fail. Football
is cheaper.

Philip Fraering
[e-mail]

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

Date: Wed, 9 May 90 20:40:46 EDT
From: John Roberts <[e-mail]>
Disclaimer: Opinions expressed are those of the sender
    and do not reflect NIST policy or agreement.
Subject: Re: Re: Dyson spheres (long)


>From: usc!cs.utexas.edu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca![e-mail]  (Christopher Neufeld)
>Subject: Re: Re: Dyson spheres?

>In article <[e-mail]> [e-mail] (Russ Cage) writes:
>>
>>Needless worry.  Here is a back-of-the-envelope analysis:
>>
>>Assume inner surface of sphere is at 500 K and radiates like a
>>blackbody.  Radiation is 3540 W/m^2 (uniformly inside the sphere).
>>
>>Surface of Sol is at roughly 5000 K, and is close to a blackbody.
>>Radiation from Sol is rougly 35,400,000 W/m^2.
>>
>>Sol will get back ~1e-4 of its own radiated output from a Dyson
>>sphere radiating uniformly at 500K, less from a cooler one.  You
>>can probably ignore this; at worst, it will be a small problem.
>>
>   Nope, it doesn't work that way. Your conclusion is correct, though.
>   Consider this back of the envelope calculation: take the sphere as a
>solid object, thin skinned compared to the diameter of the sphere, with
>equal temperatures on the outer and inner surfaces. Now, assuming that
>the total potential energy of the sphere isn't increasing, it must
>radiate as much energy to the outer surface as the Sun delivers to the
>inner surface. If the skin is thin, the area of the inside is roughly
>equal to the area of the outside. Since the two surfaces are at the
>same temperatures, the inside surface radiates as much energy as the
>outer surface, so it radiates one solar power of energy back into the
>sphere. The Sun subtends 6.8E-5 steradians of solid angle from the inner
>surface of the sphere (at 1AU). Assuming that the radiation from any
>element of the sphere is isotropic (I don't know how good an assumption
>this is), the Sun catches 1.1E-5 of the reradiation, which raises the
>surface temperature of the Sun by much less than 1 degree.

There's a much simpler approach, which I would have a greater tendency to
trust:

According to the Stefan-Boltzmann law of radiation, 'the energy radiated in
unit time by a black body is given by E = K * (T^4 - T0^4), where T is the
absolute temperature of the body, T0 is the absolute temperature of the
surroundings, and K is a constant'. (I *think* the constant K is the
Stefan-Boltzmann constant, which is 5.6696E-8 W/(m^2 * Kelvin^4) ). If
we assume that the power output of the sun is constant, that everything acts
like a black body, that the current temperature of the sun is 5000K, that the
temperature of space is about 3K, and that the inside surface of the Dyson
sphere is 500K, then putting a Dyson sphere around the sun will raise its
surface temperature by about 1/8 of a degree K. If more of the energy is
reflected inward, the effect is intensified. (Any perfectly reflecting Dyson
sphere will eventually explode.)

If I got the calculations right, a blackbody Dyson sphere at 1AU would be
heated to about 400K rather than 500K. That's still very hot - all living
quarters would have to be heavily refrigerated. That's why I wanted to put
it out at 1.4 AU - 330K would be more manageable. Come to think of it, a little
further probably wouldn't hurt. (Of course, the numbers will be different for
real-world, non-blackbody materials).

>>Re-reflecting the waste heat inside the sphere several times could
>>increase its lifting capacity in direct proportion to the energy
>>being reflected (photon momentum P = E/c).  Put that in your
>>equation and crank it.
>   Yes, but that makes the sphere less useful as a heat engine. BTW, in
>the scenario I described in the first section, each surface would see
>about three times the solar momentum flux (twice on absorption and once
>on emission) or about 1.4E-5 kg / m s. In real units, that's one
>kilogram for 425 m^2 of exposed surface, assuming solar momentum flux is
>the only force which opposes the gravitational attraction.
[Later revision]
>   I left out some geometric factors in the integrals. Unless I missed
>some others, it should be closer to 9E-6 kg / m s^2 (correct units this
>time), or one kilogram for 630 m^2 of exposed surface. This is because
>non-orthogonal incidence changes that "three times the solar momentum
>flux" to about twice the solar momentum flux (only the radial component
>of the flux is important).

Upon further consideration, I don't think the re-radiated heat will help
to inflate a sphere of black body material which radiates equally to the
inside and to the outside. Consider the situation you described (I think it
was the nonreflecting surface): as you pointed out, the sphere in steady-state
must radiate to the outside the same amount as the solar energy directly
incident upon its inner surface - about 1400 W/m^2 at 1AU. It also radiates
the same amount to the inside. According to my earlier spherical integration,
the perpendicular force vector from this radiation is reduced by a factor of
2 because the surface radiates in all directions. The inside of the sphere
absorbs 2800 W/m^2 (half from the sun, half uniformly distributed over a
solid angle of 2*pi sr from the rest of the inner surface of the sphere). The
surface of the sphere thus experiences an outward force of 1.5 times that
of the solar flux alone, and an inward force of .5 times the solar radiation
pressure. The net result is that the sphere experiences no more outward force
than if the surface radiation were ignored. (Again, if the inner surface is
reflective, the situation is different - but the black body formula has to be
modified.)

I didn't quite follow how you got some of your numbers - more detail might
be helpful.

Two books for further reading:
  "Thermal Radiation Heat Transfer" by Siegel and Howell, Hemisphere / McGraw-
Hill, 1981. (862pp, a textbook, with SI and other scales in parallel)

  "Theory of Heat Radiation" by Dr. Max Planck, 1914. (225pp, translated)

              John Roberts
              [e-mail]

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

Date: 10 May 90 04:51:18 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: SPACE Digest V11 #344

>>> The West German Space Agency plans to establish a commercial organization
>>> to operate and market its payloads on the Columbus space station.
>>                                            ^^^^^^^^^^^^^^^^^^^^^^
>>        Um, excuse me. What the h*ll this is?
>Hopefully, that was a typo. Columbus is the name of the European Space
>Agency's attached module for Space Station Freedom.

Don't be so sure.  ESA has hinted several times that they are prepared
to go it alone if the US has one more spasm of indecision about "Space
Station Fred".  (So have the Japanese.)  Presumably it would cost them
extra time to provide an independent power system, but I assume they'd
then use Hermes anyway and that's a ways down the road.

If I were them, I'd bolt now and get started.  I suspect Fred ain't
flying soon.

--
 1955-1975: 36 Elvis movies.  |  Tom Neff
 1975-1989: nothing.          |  [e-mail]

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

Date: 10 May 90 21:30:47 GMT
From: [e-mail]  (Edward Joseph Bennett)
Subject: Re: Terraforming Venus (was: Manned mission to Venus)

> I think using Saturn's rings as H2O fodder for terraforming
>Venus is a Bad Idea. There are other sources of ice in the
>Solar System, and destroying a beautiful ring sytem unecessarily
>seems wrong. Kind of similar logic to national parks or
>historic buildings. The Rings have a value where they are.
>                        JDN

Good point. We can use rings from Jupiter or Neptune or some set of
rings that is not as spectacular. Would we have to use enough of the
rings to make a noticable difference anyhow?

Ed

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

Date: Thu, 10 May 90 08:31:14 PDT
From: [e-mail] (Sam Sivakumar CH2-87, 554-5595)
To: "[e-mail]"@HERMES.intel.com
Subject: Re: Terraforming Venus

>voder!dtg.nsc.com![e-mail] writes:

>In "A Step Farther Out" by Jerry Pournelle (many years old now) he advocates
>using blue-green algae dropped in massive clouds from above. He assumes that
>these will gradually cause rain to precipitate rainstorms, which will
>slowly descend through the Venusian atmosphere, will eventually hit the
>ground and thereby cool it.

>Anyone read this and/or could comment?
--
...........................................................................
>Andrew Palfreyman        and i am dumb to tell a weather's wind
>[e-mail]        how time has ticked a heaven 'round the star
>        free energy and immortality!

    This idea (pretty nifty, in my opinion) was also discussed by Carl
Sagan in one of his books (The Cosmic Connection, I think).  The idea came
from the fact that some of the underwater thermal springs and geysers have
a host of blue-green algae living in them.  These have adapted to life at
extremely high temperatures and pressures.  While they may not survive at
the Venusian surface (900K would probably be too much), I think that the
idea was to "seed" the clouds high above the surface with several shiploads
of algae and sit back and let them do their thing.  Blue-green algae are
plants and they will, given sufficient time, convert the CO2 into oxygen.
I am not very sure, though, about whether this is practical.  However, if
it would work, what better way can there be! (Look, honey ... biodegradable
terraformers :-)

    I wonder if any biologists reading this thread would care to
provide some numbers on this approach.

---------------------------------------------------------------------------
Sam Sivakumar            |   M/S CH2-87 Intel Corp. |   [phone] (O)
[e-mail] |   5000 W. Chandler Blvd. |
                         |   Chandler, AZ 85224     |

            "Don't have a cow, man!!" -- Bart Simpson (radical dude)
---------------------------------------------------------------------------

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

Date: 10 May 90 08:18:00 GMT
From: mcsun!hp4nl!philapd!ssp17![e-mail]  (Gordon Booman)
Subject: Re: Voyager Confirms Relativity

In article <[e-mail]> [e-mail] (Arnold G. Gill) writes:
>... all the evidence points to quasars being at far extragalactic distances...

I'm not sure that that "all" is justified, but there certainly is more
evidence than just the red-shift for quasars being distant, as many people
have informed me by mail.  I thank everyone that has replied.  I feel a
little better about the standard model now (but not entirely convinced :-).

I hope everyone agrees that it is important to occasionally step back and
consider what slender supports we sometimes build our models on.

The universe would be pretty boring if we were always right, wouldn't it?
--
Gordon Booman SSP/v2b25  Philips TDS Apeldoorn, The Netherlands  [phone]
domain: [e-mail]             uucp:  ...!hp4nl!philapd!gordon

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

Date: 8 May 90 16:17:00 GMT
From: swrinde!zaphod.mps.ohio-state.edu!brutus.cs.uiuc.edu!ux1.cso.uiuc.edu!ux1.cso.uiuc.edu!m.cs.uiuc.edu!bucc2![e-mail]
Subject: Re: A Non-military economy possibility


>/* Written  6:04 pm  May  5, 1990 by cis.udel.edu!pezely in bucc2:sci.space */
>/* ---------- "A Non-military economy possibility" ---------- */
>
>The show was Bill Moyers (I think), and the interview was with a
>professor at Columbia University in New York City.  I believe the
>professor's name was Melman or Melmak....
                                ^^^^^^
                            Been watching too much ALF, eh? :-)

>They were talking about swithching from a military enconomy to a
>civilian one.  My question is, why not a SPACE ECONOMY?
>
>The problem with switching to a civilian economy, they said, was that
>the DOD contractors would have to lay-off lots of people.
>
>But, if you look at who the DOD contractors are, you'll see that most of
>them are also heavilly into aerospace.  Hmm.  That solves the problem
>with laying-off the factory workers, and the engineers and creative
>people just switch departments.
>
>It's just a thought.  Don't send me mail because I wont reply to it,
>and I wont be checking the newsgroups to see the follow-ups.

    Minor question: Why post if you don't care about others' ideas
    on the same subject? Or are you leaving school for vacation,
    as I will rather soon as well?

>-Dan
>Computer Science Lab, Smith Hall, University of Delaware, Newark, DE 19716
>[e-mail];  Lab: 302/451-6339,fax: [phone];  Home: 302/368-5931
>*** BITNET: a nice place to visit, but I wouldn't want to live there.  ***

    These are ideas that are long overdue. I mean we here knew
    that, to quote Arthur Clarke, that space exploration was
    "...the moral equivalent of war" (2061), but what I think will
    really happen is that, yes, these industries may turn to
    space, and yes, NASA might actually get a hefty increase in
    its budget (for a change), but the majority of the "peace
    dividend" is actually going to go to payments on the deficit.

    Naturally, since I am no prophet, this is all IMHO.

As of 5/16/90, no answers to mail, but 'till then:
Craig\The Moonman\Levin
Bitnet {?}: [e-mail]      |  uiucdcs\
Internet: [e-mail] |      noao>bradley!bucc2!moonman
I'm just an undergrad. THEY don't   |     cepu/
care if I have opinions or not.     |

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

End of SPACE Digest V11 #387
*******************