Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V10_2/V10_273.TXT

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Subject: SPACE Digest V10 #273

SPACE Digest                                     Volume 10 : Issue 273

Today's Topics:
          Re: Steam powered solar power sats (SPSPS)
           NASA Space archive service now available
                 Shuttle Book
          Re: Steam powered solar power sats (SPSPS)
            Re: Moon Colonies / Ant Tanks?
           Re: Why NASA wants to go to Mars
             Re: Viewing Earth w/the HST
----------------------------------------------------------------------

Date: 23 Nov 89 21:26:36 GMT
From: daisy.learning.cs.cmu.edu![e-mail]  (Marc Ringuette)
Subject: Re: Steam powered solar power sats (SPSPS)

paj@mrcu (Paul Johnson) writes:
> [Everybody] seem to be proposing solar power satalites
> using square miles of solar cells.  Why not use mirrors (cheap &
> light: make them out of sodium) and run a steam turbine.

Using a large mirror plus a high-temperature generator is a great idea for
space power production, as far as I can tell.  A turbine containing water
or some other fluid is one possibility.  An alternative to turbines is
thermionic power conversion.

Thermionic Power Conversion (TEC)
---------------------------------
The idea of TEC is to heat up an electrode until electrons are moving so fast
that some of them can jump across a potential gap.  If you make sure the
other electrode isn't as hot, so the electrons don't jump back, you can use
this to drive an electrical load.

It looks like a winner.  It has no moving parts, turns a temperature difference
directly into electricity, doesn't use up any material, and works at high
temperatures for a good power-to-weight ratio.

The research was mostly done at NASA Lewis.  A 1981 article in Horton's book
(references below) cited these figures:

  input power densities of up to 100 Wt/cm/cm (Wt = watts total)
  output power densities 10-40 We/cm/cm  (We = watts electrical)
  operating temperatures 1300-1900K input
               900-1500K output
             500-1000K differential gives 10-40 We/cm/cm

Note that the power densities are in watts per unit area, rather than watts
per kilogram.  I have figures for solar flux level in outer space of 0.1 to
0.15 W/cm/cm, so an input flux of 100 Wt/cm/cm is about 700-1000 times that
of ambient sunlight.

Another 1966 paper from the Szego book, from JPL, has a TEC working at
24 W/cm/cm, weighing 260g, producing 48W at 2000K emitter temperature.
Pretty good power densities for that early stage.

The Radiator
------------
Most space power systems are driven by a temperature difference.  This
difference must be maintained by some sort of radiator on the cool side of
the generator.  The radiator can often be the heaviest part of a system.
However, the higher the temperature, the more energy you can radiate, which
is an advantage for a TEC or turbine system.

In fact, some TEC systems are configured so as not to need an external
radiator; they operate at high enough temperature that the necessary
temperature gradient can be maintained by merely keeping one side dark.
One article is by Shimada and Ewell of JPL, in the Horton book; the power
densities weren't spectacular, though.

If you use a radiator, the basic design conducts heat to a set of radiating
fins, by fluid flow or a heat pipe.  There are some untested but interesting
alternatives like the one Keith Henson pointed out, which use dust or gas to
increase the ratio of surface area to weight in the radiator.

References
----------
Finke, Electric Propulsion and its Application to Space Missions, AIAA, 1981
Horton, ed., Spacecraft Radiative Transfer and Temperature Control, AIAA, 1981
Szego & Taylor, Space Power Systems Engineering, AIAA, 1966

Summary
-------
Cool stuff, and potential for orders of magnitude improvement in space
power generation.  If you like to think about this kind of stuff, you might
want to join 'space-tech', a mailing list I run.  We talk about all sorts
of ideas for space transportation and exploration, with emphasis on working
out the physics of what's going on.  To join or ask for more info, send mail
to '[e-mail]' on the Internet.


--  Marc Ringuette  //  CMU CS Dept, Pittsburgh  //  Internet: [e-mail]

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

Date: 22 Nov 89 07:08:17 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: NASA Space archive service now available

I've added an extra directory to the archive server running on
ames.arc.nasa.gov.  Now, if you miss a status report posting, or you
want to read back issues of NASA Headline News, you can!  The archive
is available via both anonymous ftp and archive-server mail response.

Instructions:

    Anonymous FTP

    ftp to ames.arc.nasa.gov (128.102.18.3).  Cd to pub/SPACE.
    Get any of the files you want.  The file index contains a
    listing of what's available.


    Archive-server mail response

    Send a letter to [e-mail] (or to
    ames!archive-server, or ames::archive-server).  As the
    subject of your message you may send commands like:
    "send space index" or "send space STS-34.Press-Kit".
    Send the command "help" for more detailed instructions
    on how to use the archive-server.


File names:

    Generally files are named by type and date.  For example, the
    Shuttle Status report for this morning would be named
    ss11.21.89.  Common prefixes are "ps" for Payload Status,
    "h" for NASA Headline News, "r" for Press Release, "ss"
    for Shuttle Status, "gs" for Galileo Status", "ms" for
    Magellan Status, "cs" for COBE Status, "la" for Launch
    Advisory, etc.  There are also several other files with
    more descriptive names.


Problems:

    Send me e-mail if you have problems accessing the archives.


Start of Service:

    I started filling the archive yesterday, so there isn't much there
yet.


                            -Peter Yee
                            [e-mail]
                            ames!yee

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

Date: 20 Nov 89 10:54:30 GMT
From: mcsun!ukc!strath-cs!cs.glasgow.ac.uk![e-mail]  (Mr Kevin Waite)
Subject: Shuttle Book

Can anyone recommend a good medium-level text on the Space
Shuttle that concentrates on the technical issues rather than
the political ones.  By 'medium-level' I mean something between
the "the Space Shuttle is a spaceship" level and the "design
of turbopump turbine blades" level.

Thanks in advance.
Kevin

--
Email:   [e-mail]  (JANET)
     [e-mail]  (INTERNET)
Address: Dept. of Computing Science,  University of Glasgow,
     17 Lilybank Gardens,  Glasgow,  United Kingdom.  G12 8QQ

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

Date: 23 Nov 89 17:45:43 GMT
From: cs.utexas.edu!samsung!shadooby!mailrus!jarvis.csri.toronto.edu!ists!yunexus!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Steam powered solar power sats (SPSPS)

In article <[e-mail]> paj@mrcu (Paul Johnson) writes:
>...he and everyone else seem to be proposing solar power satalites
>using square miles of solar cells.  Why not use mirrors (cheap &
>light: make them out of sodium) and run a steam turbine...

Actually, one would use aluminum rather than sodium.  Just as good, if
not better, as a mirror (most astronomical telescopes use it), and not
nearly the hassle to handle.  Aluminum mirrors can be very thin; 30nm
of aluminum is still highly reflective.

The main problems with solar-dynamic powersats are (a) moving parts
and (b) greater sensitivity to structural distortions and inaccurate
Sun-pointing.  Also, there is very little experience with solar-dynamic
power systems in space.  A solar-dynamic powersat is probably a better
design, but as of today it's also a riskier design.

>BTW, how much would solar cell production by the square mile damage
>the environment?

Depends on the type of cell.  Silicon is no big deal.  Gallium arsenide
is a bigger problem, due to highly toxic materials.  The best place to
build parts for power satellites is, in any case, either in space or on
the Moon.

>Similarly, for power down to Earth, everyone assumes microwaves.  Why
>not set up an antimatter factory in orbit and ship a few milligrammes
>back down to Earth every so often?

With current designs, antimatter production is *very* inefficient, and
using antimatter for power production is not great either.  The big
advantage of microwaves is that the conversions to and from electricity
are quite efficient.
--
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry [e-mail]

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

Date: 23 Nov 89 18:24:48 GMT
From: mailrus!jarvis.csri.toronto.edu!ists!yunexus!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Moon Colonies / Ant Tanks?

In article <[e-mail]> [e-mail] (Mark Gellis) writes:
>... this means you have to have
>carbon as an initial material.  How common is carbon in the solar
>system (not counting hard to reach places like the core of the sun)?

Quite common, actually, although it tends to be associated with volatile
compounds and hence isn't common on the Moon.  Barring that, it is one
of the half-dozen commonest elements for quite fundamental reasons.
The solar system has lots of carbon dioxide and methane, although much
of it is not in the most convenient places.  There is, however, a useful
amount of carbon in certain classes of meteorites and hence very probably
in certain classes of asteroids.

>Could it be, say, extracted from the ice/junk surfaces of the moons
>of the gas giants?

Reasonably likely, picking the colder moons, although it is difficult to
be sure since our knowledge of the surface compositions of those moons
is somewhat indirect.

>Second, for anyone who knows anything about fusion reactions, also
>related to carbon.  If you have controlled fusion power (which we
>should have sometime in the next hundred years), can you simply make
>carbon from helium? ...

Only with great difficulty.  Controlled fusion will not be up to doing
that in useful quantities for a long time, barring some major breakthrough.
The helium->carbon reaction is geologically slow under conditions that are
likely to be practical in the near future.  (It's not exactly fast even in
most stars.  It requires *three* helium nuclei colliding in the right way,
as there is no stable intermediate that could be formed by collision of two.)

>Fourth, O'neill has his space habitat as a 6.4 km x 32 km. cylinder.
>Is there any reason why a cylinder in space could not be made longer?
>Could you build a 6.4 km. x 320 km. cylinder, for example...

Ideally, no problem.  But there are various non-ideal complications.
Tidal forces need considering if you're doing this anywhere near the
Earth or the Sun, for example.  For another example, a spinning object
generally prefers to spin end over end (formally:  on the axis with
the greatest moment of inertia).  A rigid object is not capable of
changing its spin axis... but no hollow cylinder kilometers across is
rigid in any realistic sense.  Spinning satellites have to be designed
quite carefully to keep the spin axis where it belongs.  I'm not sure
O'Neill thought of this...  The problems will get worse as the cylinder
gets longer.
--
That's not a joke, that's      |     Henry Spencer at U of Toronto Zoology
NASA.  -Nick Szabo             | uunet!attcan!utzoo!henry [e-mail]

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

Date: 23 Nov 89 05:14:12 GMT
From: frooz![e-mail]  (Bill Wyatt)
Subject: Re: Why NASA wants to go to Mars

[...]
< From "Aviation Week and Space Technology," Oct. 30, 1989 (p.15):
< Franklin D. Martin, NASA's associate administrator for exploration, has a
< host of reasons for sending humans to Mars.  [...]
<   "Hey, Frank, you left off science," [...]
<   "Yeah, maybe so.  Yeah," [...] "science is
<    one of the reasons you do these things, but it's not the driver."
<
< Am I the only one who nearly became physically ill after reading this?
< Is this truly what our space program has become, a bunch of administrators
< who are no longer aware that space exploration is meant for science?
< [...]
<  If any of you hopeful ones needed proof of the final
< collapse of the United States' space program, here it is.

Yes, I agree the (U.S.) space program is near collapse, and
YES I agree that sending men to Mars is not done because of
science.

If you want to do space research, there are a hell of a lot
better and more productive ways to spend your money than by
putting people up there. There's a small class of problems
that would benefit by human presence, but there's a long way
to go before you've exhausted the worthy unmanned projects.

As an example: test the absurdity, given present levels of
technology and more reasonable alternatives, of the
following statement:

`We must must embark on a program to send men to Pluto, since
 the Voyagers didn't get out there to take any pictures and
 give us a close-up view of the Pluto-Charon system.'

I'm not against a manned space program, but I do think it's a
crime the way NASA fixates on bloated projects at the expense
of space science, and turns around and denys there's any
alternative. Don't you believe that science has EVER been a
driver for the manned space program; it has ALWAYS been
primarily a politically and then technologically motivated
operation.

The scientific gains have been a bonus, not a driver, ever.

Bill Wyatt, Smithsonian Astrophysical Observatory  (Cambridge, MA, USA)
    UUCP :  {husc6,cmcl2,mit-eddie}!harvard!cfa!wyatt
    ARPA:   [e-mail]
    SPAN:   cfa::wyatt                 BITNET: wyatt@cfa
Bill Wyatt, Smithsonian Astrophysical Observatory  (Cambridge, MA, USA)
    UUCP :  {husc6,cmcl2,mit-eddie}!harvard!cfa!wyatt
    ARPA:   [e-mail]
    SPAN:   cfa::wyatt                 BITNET: wyatt@cfa

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

Date: 22 Nov 89 15:49:24 GMT
From: gem.mps.ohio-state.edu!uakari.primate.wisc.edu!larry![e-mail]  (Scott Ellington)
Subject: Re: Viewing Earth w/the HST

The sunlit earth is far too bright to be observed by any of the HST
sensors.  In any case, the guidance system cannot slew anywhere near
fast enough to track a target on the surface of the earth.

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

End of SPACE Digest V10 #273
*******************