X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
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Tue, 14 May 91 01:26:48 -0400 (EDT)
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Date: Tue, 14 May 91 01:26:40 -0400 (EDT)
Subject: SPACE Digest V13 #541
SPACE Digest Volume 13 : Issue 541
Today's Topics:
NASA Prediction Bulletins, Part 1
Re: Why the space station?
--> People working at the JPL <--
Re: Why the space station?y
Re: Gas Guns and Tethers
Administrivia:
Submissions to the SPACE Digest/sci.space should be mailed to
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should be sent to space-request+@andrew.cmu.edu, or, if urgent, to
In article <1991May7.024811.8157@uokmax.ecn.uoknor.edu> rwmurphr@uokmax.ecn.uoknor.edu (Robert W Murphree) writes:
>
>In summmary, the plausibility of the sequence "first you build reliable
>space transportation, then you build a orbital space base, then you go
>to the planets" is seriously in question. All you really need to do
>important space science is a big booster -a titan IV. The head of the
>space telescope institute-Giaconni has said that he would much rather
>launch the space telescope into high eliptical orbit and then replace it
>with a new copy than low orbit with manned servicing. The real reason
>for the space station is an ignorant past president who probably consulted
>his wife's astrologer to determine which day to announce the space station.
>The space station is pure pork.
If you assume that you are never going to do large scale in space assembly
and that you are never going to need to launch really large probes into
deep space or to the planets using exotic propulsion systems, or if you
assume that large scale human presence in space is never going to occur
and that you don't need life science data for long term zero G existence,
then a space station is a pork barrel. Otherwise, it is the logical next
step. A valid question is whether Fred is that space station, but the need
for a space station remains.
The situation with space scientists is similar to the idea of using
dugout canoes for transoceanic exploration rather than wasting money
developing proper ocean going vessels simply because it impacts *their*
pet projects *now*. Space will still be there twenty or thirty years from
now. Developing the proper transportation systems to make deep space more
easily and cheaply accessable will, in the long run, make space science
much more productive.
Gary
------------------------------
Date: 9 May 91 02:34:02 GMT
From: csus.edu!wuarchive!sdd.hp.com!mips!pacbell.com!iggy.GW.Vitalink.COM!widener!dsinc!ub!ubvmsc.cc.buffalo.edu!v096my2q@ucdavis.ucdavis.edu (Mark A Wieczorek)
Subject: --> People working at the JPL <--
Hello to everybody working at the JPL! I got a job through
the Planetary Geology and Geophysics research program working on the
Magellan mapping project this summer at the JPL. I would be interested
in talking to people who are currently working on this project and know
what is going on. I keep getting lots of cool maps of venus and manuals
on the spacecraft in the mail, but I only have a very vague idea of
what people do who are working on this project. I was told that depending on
my interests I could be working on the mapping project, developing planetary
models or working with various computer related things. Well I have a physics
background with almost no geology, but hey, they knew what they were
paying for! I'd be interested in hearing from people who are specifically
working in some way with the magellan so I could learn more about what
is done and what I could be doing. If you have some spare time please
write me at:
v096my2q@ubvms.cc.buffalo.edu
Mark Wieczorek
------------------------------
Date: 10 May 91 00:43:07 GMT
From: hub.ucsb.edu!ucsbuxa!3001crad@ucsd.edu (Charles Frank Radley)
Subject: Re: Why the space station?y
collision risk is smaller for Freedom with Shuttle than Progress
with Mir. The Shuttle is manned with several crewmembers watching
the proceedings.
------------------------------
Date: 9 May 91 03:19:43 GMT
From: sdd.hp.com!cs.utexas.edu!news-server.csri.toronto.edu!torsqnt!hybrid!torag!w-dnes!waltdnes@ucsd.edu (Walter Dnes )
Subject: Re: Gas Guns and Tethers
wreck@fmsrl7.UUCP (Ron Carter) writes:
> In article <ce7711w163w@w-dnes.UUCP> waltdnes%w-dnes@torag.uucp writes:
> [regarding capturing sub-orbital payloads with a tether]
> >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.
>
> This is not a problem. It requires only:
> a.) that the decrease in the size of the orbit be managable, or
> b.) the opposite end of the orbit be higher to compensate.
>
> Yes, so? Is an absolutely constant orbit a requirement? For what?
>
Note that the orbit has dropped. It will drop *EACH TIME THAT
YOU REEL IN A SHUTTLE*. Do it often enough, and you'll be cruising at
the top of the atmosphere... "Son of Skylab". Of course you could
fire a rocket engine to boost the combined spacestation-and-shuttle
back up. But that would be equivalent to having fired the shuttle up
to the higher orbit in the first place !!! Reeling in the shuttle to
raise its orbit is no different than firing the shuttle's engines
to raise its orbit. In both cases you're looking at raising an object
against gravity. The net work is the same...
_ r=GEO
/ Where G = gravitational constant
| GMm GMm GMm M = mass of earth
| --- dr = --- - --- m = mass of shuttle
| r^2 LEO GEO LEO = radius of Low Earth Orbit
_/ GEO = Geosynchronous Earth Orbit
r=LEO all orbital radii relative to centre of earth
> If you'd take a detailed look at the energy and angular momentum
> transfers, you'd realize that tethers don't offer a free lunch, or
> a free launch. What they give you is checking and credit, letting
> you loan or transfer energy and angular momentum w/o using rockets.
In another reply on this thread, I made a glaring error that
would seem to allow this scheme to work. I assumed that a shuttle
could be "reeled out". ( Silly me, I'll never graduate to sci.skeptic
this way. ) If the shuttle detaches and the main station unreels
several thousand miles of tether... you'll merely end up with an
atrocious "crowsnest" like no fisherman has ever seen before. The
shuttle will tend to remain in the same orbit as the station, *UNLESS
IT FIRES ITS ROCKET ENGINES TO DE-ORBIT*. That's what the shuttle has
to do right now.
Our disagreement seems to boil down to this...
I see 2 expenditures of energy; raising the shuttle from LEO to
GEO, and then dropping from GEO to LEO. You seem to believe that two
shuttles (1 coming, 1 going) can cancel each other out. I.e. you think
that energy can be transferred from one shuttle to the other. I think
that you've run afoul of the 2nd law of thermodynamics (entropy) with
something resembling Maxwell's demons that could filter cold and hot
molecules in a gas. Rather than us making general statements to each
other, how about you coming up with a solution that is consistent with
known physical laws and posting it here ? It only takes one counter-
example to prove me wrong. Can you do it ?
Walter Dnes (Please tell me I got the headers right this time)
