X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
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Wed, 1 May 91 01:27:52 -0400 (EDT)
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Date: Wed, 1 May 91 01:27:43 -0400 (EDT)
Subject: SPACE Digest V13 #485
SPACE Digest Volume 13 : Issue 485
Today's Topics:
Re: Saturn V and Design Reuse: Saturn VI?
Re: Transportation Tethers (Beanstalks)
Scientific Humor
NASA Prediction Bulletins: Space Shuttle
Re: Terraforming Mars? Why not Venus?
Re: Gas Guns and Tethers
Gif files
Re: Saturn V vs. ALS
Re: new gifs available
Re: HOW TO TELL IF Re: Galileo works?
Administrivia:
Submissions to the SPACE Digest/sci.space should be mailed to
space+@andrew.cmu.edu. Other mail, esp. [un]subscription requests,
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mars. There is a huge amount of corrosive acid on the surface, let alone the stuff in the atmosphere. If you were to convert the atmosphere, there would still be acid/methane etc.etc.etc vaporising from pools on the surface. The other problem is the vulcanism and earthquakes. there is no way you are going tobe able to stop them with a little [little?] catalyst. ther are mainly a result of the spin of the planet and the greater gravitational disturbences of the sun.hence, you would clean up the p
lanet but have your buildings flattened fast.
If you were really set on the terraformation of Venus, and you had some pretty
hot technology, you could calculate the interference caused by the sun and the magnetic flow caused by the planets spin and SLOW DOWN THE PLANET to the required level. [about that of earth] and the vulcanism/earthquakes would slow and probably drop to a more manageable level after a while [while defined as a minimum period of a few centuries!!]. Well, that's my eight cents worth.
katani.
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Date: 30 Apr 91 03:33:23 GMT
From: agate!bionet!uwm.edu!wuarchive!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo!utdoe!torag!w-dnes!waltdnes@ucbvax.Berkeley.EDU (Walter Dnes )
Subject: Re: Gas Guns and Tethers
eder@hsvaic.boeing.com (Dani Eder) writes:
>
> This ignores the fact that you do not have to have a tether all
> the way from orbit to the ground. A shorter tether hanging vertically
> in orbit will have it's lower end moving sub-orbitally. A launch
> system then only has to reach the bottom of the tether, rather than
> orbit. Anything that makes a launch vehicles' job easier is
> beneficial. The reminder of the ride to orbit (which is at the
> center of mass of the tether) can be via elevator.
> ___
|___| Space I think that you've fallen into the old
| station "pull-yourself-up-by-your-bootstraps" fallacy. Here's a
| simplified diagram of the situation, just before the
| launch vehicle grabs the bottom of the tether. Assuming
| that the mass of the tether is small relative to the main
| station, the centre of mass of station+tether will be near
| the space station itself. When the shuttle grabs the
| |===| tether, we have a new body, i.e. station+tether+shuttle.
shuttle You have three problems to deal with...
Theoretical problem 1) The centre-of-mass of the combined structure has
instantaneously dropped closer to the earth's surface without the orbital
velocity increasing. The result should be a lower orbit.
Theoretical problem 2) Remember my "Summary:" line about no boostrapping?
As the shuttle climbs the tether, the space-station+tether descend a bit.
Since we're dealing with a closed system, the centre-of-mass must remain
in the same orbit.
Practical problem 1) Conservation of angular momentum... Unless the
shuttle matches velocity *VERY* closely with the station, the two bodies
will be spinning around each other at some horrendeous rpm's by the time
the shuttle has climbed all the way up the tether.
The theoretical problems are where many "perpetual-motion machines"
trip over reality. It takes X joules of work to lift a specific payload
to a specific orbit. TANSTAAFL... There Ain't No Such Thing As A Free
Lunch. Rather than a tether, how about a "Tower of Babel", reaching up
to GEO ? Technologically impossible, but good for a sci-fi story or two.
At least in the stories, you could take an elevator to the top. Where
