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Date: Sat, 23 Feb 91 01:59:02 -0500 (EST)
Subject: SPACE Digest V13 #194

SPACE Digest                                     Volume 13 : Issue 194

Today's Topics:
		     Re: Terraforming, sun shield
     Re: Commercially-funded Space Probes (was Re: Space Profits)
		    Re: Magellan Update - 02/20/91
      UN Moon Treaty (was Re: Commercially-funded Space Probes)
			 Re: nuclear rockets
			   Re: Doing What?

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

Date: 22 Feb 91 07:13:55 GMT
From: usc!samsung!crackers!m2c!jjmhome!lectroid!STRATUS.COM!tarl@rutgers.edu  (Tarl Neustaedter)
Subject: Re: Terraforming, sun shield

In article <5705@optilink.UUCP>, cramer@optilink.UUCP (Clayton Cramer) writes:
|> In article <28676.27c07594@kuhub.cc.ukans.edu>,
2fmzmumble@kuhub.cc.ukans.edu writes:
|> > Problem:  Terraform Venus.  Method:  Orbit a large shield in front
of the sun
|> > to cut incident visible sunlight by 50%.  Assume:  Manufacturing
and
|> 
|> First problem -- it's own gravitation would cause it crush down to a
|> little sphere in no time.  Any object with a mass equivalent to a
|> 200 mile sphere conforms itself into a round shape, rapidly.  I'm
|> afraid your shield won't last.

Not necessarily. You could have the shield be spin-stabilized, which
requires
that the material be stretch and tear resistant but doesn't require any
particular rigidity.

As for maintaining position, the obvious answer is to put the shield in
the
lagrange-2 position between the sun & venus (refer to A.E.Roy's Orbital
Motion,
ISBN 0-85274-229-0 or any standard celestial mechanics text for details
on
lagrangian points), and some small active measures to maintain position
(this
lagrange point is unstable, so you have to continually correct your
position).

Since you're talking a large object with small mass, you could also use
Robert
Forward's "statite" concept (see Analog about 3-4 months ago, he also
has filed 
for a patent). In this concept, the light pressure on the object itself
is used
for thrust; A solar sail. There are limits in which directions the
thrust can 
be applied, and you probably have to balance object mass against amount
of
thrust available. Since the amount of thrust is defined by the amount of
sunlight
that you are blocking, you may actually have to add mass to your object
to get
the effect desired. You also need to use some of the thrust off-axis to
precess
the object about 1.5 degree/day so that the face stays pointing at the
sun
(this actually means having the center of thrust offset from the center
of mass,
and has all the wondrous problems of torque on a spinning object).

If your object has no external thrusting available except light
pressure, you
would have to put it inside the L2 point (closer to the sun than 0.85 of
venus
orbit, roughly 16 million km from venus), and have the thrust be
directly away
from the sun (to account for the fact that you have to travel slower
than orbital
velocity to keep station with an object outside of your orbit).
According to the
back of my envelope, at that distance an object with a diameter of
200,000km
produces a pinpoint umbra on the center of venus. The rest of venus is
in a 
dense penumbra, so you've managed to cut out almost all of the sunlight
reaching
venus. Reduce the diameter to increase sunlight on venus.

Once you determine how much sunlight you want to arrive, you can derive
the size
(diameter) of the object, and then you can derive mass and thrust
figures as well.
	Tarl Neustaedter

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

Date: 22 Feb 91 17:50:25 GMT
From: bonnie.concordia.ca!news-server.csri.toronto.edu!utzoo!henry@uunet.uu.net  (Henry Spencer)
Subject: Re: Commercially-funded Space Probes (was Re: Space Profits)

In article <YAMAUCHI.91Feb21170759@heron.cs.rochester.edu> yamauchi@cs.rochester.edu (Brian Yamauchi) writes:
>would there be any interest in commercially-funded space probes to
>survey resource deposits in the asteroids, comets, Jovian moons, Moon,
>Mars, etc?

Very little.  With the staggering costs of space transportation at present,
it is very difficult to devise a scheme for exploiting such resources that
could show a profit.  Worse, any such venture is very long-term and quite
risky by investment standards, which means that the payoff has to be huge
to make it worthwhile.  So far the market is very dependent on things like
in-space activity -- importing space materials back to Earth is just too
expensive at current launch prices -- and so the market is very uncertain
and nobody wants to take a chance on it.

>Part of the question is whether any companies have the foresight to
>invest millions now to receive a return of billions in the future.

If those billions looked like a sure thing, there would be no shortage.
The trouble is that they are very uncertain billions.

>If American corporations are too short-sighted, are European and Japanese
>companies any better?

Not very much.  They're still in business to make money, and taking huge
long-term risks is not usually in their best interests.  The Japanese are
mildly interested, but not to the point of spending hundreds of millions
of dollars on early exploratory missions.
-- 
"Read the OSI protocol specifications?  | Henry Spencer @ U of Toronto Zoology
I can't even *lift* them!"              |  henry@zoo.toronto.edu  utzoo!henry

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

Date: 22 Feb 91 15:59:22 GMT
From: magnus.ircc.ohio-state.edu!zaphod.mps.ohio-state.edu!rpi!uupsi!sunic!lth.se!newsuser@tut.cis.ohio-state.edu  (Magnus Olsson)
Subject: Re: Magellan Update - 02/20/91

In article <1991Feb21.022020.1935@jato.jpl.nasa.gov> baalke@mars.jpl.nasa.gov (Ron Baalke) writes:
>
>                        MAGELLAN STATUS REPORT
>                           February 20, 1991
[...]
>     The M1051 mapping command sequence with its associated radar control
>parameter and mapping quaternion files was successfully sent to the spacecraft
			^^^^^^^^

Are these the quaternions of Hamilton (i^2=j^2=k^2=ijk=-1)? And, in that
case, what does quaternions have to do with the mappin of Venus?

Magnus Olsson                   | \e+      /_
Dept. of Theoretical Physics    |  \  Z   / q
University of Lund, Sweden      |   >----<           
Internet: magnus@thep.lu.se     |  /      \===== g
Bitnet: THEPMO@SELDC52          | /e-      \q

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

Date: 22 Feb 91 17:44:41 GMT
From: rochester!sol!yamauchi@louie.udel.edu  (Brian Yamauchi)
Subject: UN Moon Treaty (was Re: Commercially-funded Space Probes)

In article <9324@hub.ucsb.edu> 3001crad@ucsbuxa.ucsb.edu (Charles Frank Radley) writes:

   +  The other part is the question of when space law will catch
   +up and  establish guidelines for property rights in space.
   +There are enough  asteroids and enough open territory on
   +planets and moons that I can't  imagine too many fights over
   +the same resource deposit.  On the other  hand, we need a way
   +for a company to obtain rights to minerals on a  world without
   +being able to claim the entire world (and prevent others  from
   +mining it).

     Unfortunately you are too late.   The United Nations Treaty on
   the Activities of States on the Moon and all Celestial Bodies,
   already prohibits the private property rites which you address.
       The resources of the solar system beyond earth are defined as
   Res Publica.   This somewhat ill-defined term more or less
   translates as the common heritage of mankind.  I believe this
   language is also used in the Law of the Seabed treaty.
       It calls for an international regime to regulate and TAX all
   revenues or extra-terrestrial mining operations of all member
   states.   Member states are not permitted to authorize private
   mining operations.

Yes, this treaty would have killed private enterprise in space -- if
it had been ratified.  Fortunately, the L5 Society came to the rescue
and convinced Congress NOT to ratify the Moon Treaty.  In fact,
according to NSS literature, no major nation has ratified the Moon
Treaty.  This is without question the single most important action
taken by a pro-space organization.  It's reassuring to know that a
group of space activists could triumph over the political power of the
UN in this matter.

Evidently, this treaty comes up for review again in 1992.  Anyone know
whether there is a serious risk of having it ratified this time?

      I hope you do not plan to defy the United Nations.......these
   days that can become very unpleasant.

Actually, it's only unpleasant if you're a third world nation.  If
you're on the Security Council, you can do whatever you please -- it's
one of the fringe benefits of being a superpower.
--
_______________________________________________________________________________

Brian Yamauchi				University of Rochester
yamauchi@cs.rochester.edu		Department of Computer Science
_______________________________________________________________________________

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

Date: 22 Feb 91 12:41:06 GMT
From: wuarchive!rex!samsung!umich!dgsi!gregc@louie.udel.edu  (Greg Cronau)
Subject: Re: nuclear rockets

In article <1991Feb20.155444.6762@watdragon.waterloo.edu> jdnicoll@watyew.uwaterloo.ca (James Davis Nicoll) writes:
>In article <620@newave.UUCP> john@newave.mn.org (John A. Weeks III) writes:
>>
>>The Pluto missile had a few startling side effects.  It left a trail of
>>radiation that severly contaminated its path.  It also left any animal or
>>person in its path deaf.  Finally, with unlimited range, it was possible
>>that one could get loose and not be stopped, eventually killing all life
>>on Earth.  Sounds like fun...
>
>	Warning: Very Tangental Trivia Question follows
>
>	I have these really dim memories of watching a movie back in the
>60s about something that acted like that; lots of scenes consisting of
>Norman Rockwell families together, followed by the screen going white.
>The good guy dies of radiation poisoning doing something that stops the
>runaway. Anyone have any idea what the film was called.
>
>							James Nicoll				

 Funny thing. When I first read this article, it also reminded me of that
movie. In the movie, people were not just being killed by the radiation, but
by the enormous heat of the object passing overhead. Basic plot:
	Alein thingy from gawd-knows-where goes into high speed(mach 30+) low
earth orbit(10,000 feet?) and *doesn't* burn up. Has outer skin made of
super-duperium. It's also under acceleration. It also appears to be robotic.
Attempts to destroy it with missles fail because they can't get through the
instensely heated plasma ball surrounding the thingy. Can't remember how they
destroy it. Can't remember the name of the movie either, sorry. Seem to
remember that it wasn't too bad from a scientific standpoint, but it's
probably been 15-20 years since I saw it.

gregc@cimage.com

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

Date: 22 Feb 91 17:40:05 GMT
From: swrinde!zaphod.mps.ohio-state.edu!caen!engin.umich.edu!theslim@ucsd.edu  (Eric Michael Slimko)
Subject: Re: Doing What?

In article <MCDANIEL.91Feb21122530@dolphin.adi.com>, mcdaniel@adi.com
(Tim McDaniel) writes:
> In article <1991Feb21.022020.1935@jato.jpl.nasa.gov>
> baalke@mars.jpl.nasa.gov (Ron Baalke) writes:
> 
>    ... the Pioneer [Venus] orbiter is still very active.
> 
> Doing what?  I see the progress reports for old probes: "Pioneer 11
> attempted a UVS on MX2718281828.".  Are these UVSes scientifically
> useful?  Are any of these probes doing anything scientifically useful?
> (Well, I know the far-out ones are looking for a heliopause, but what
> else?)
> 
> In particular: is the Pioneer Venus orbiter collecting optical images
> or using its radar (if any)?  If not, why not, and what other
> instruments does it have?
> 
> Tim McDaniel                 Applied Dynamics Int'l.; Ann Arbor,
Michigan, USA
> Internet: mcdaniel@adi.com                UUCP:
{uunet,sharkey}!amara!mcdaniel

I believe Pioneer Venus Orbiter is being used for gravity field research
of Venus.  Don't quote me on this, but I remember hearing that somewhere.
(Its possible they were using OLD PVO data for the studies, I'm not sure)

Eric Slimko
theslim@caen.engin.umich.edu

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

End of SPACE Digest V13 #194
*******************