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From: wmartin@brl-tgr.ARPA (Will Martin )
Newsgroups: net.space
Subject: Re: Shuttle External Tanks and Space Stations
Message-ID: <586@brl-tgr.ARPA>
Date: Wed, 11-Dec-85 13:52:24 EST
Article-I.D.: brl-tgr.586
Posted: Wed Dec 11 13:52:24 1985
Date-Received: Fri, 13-Dec-85 20:08:57 EST
References: <8512011611.AA12940@s1-b.arpa> <6196@utzoo.UUCP> <6205@utzoo.UUCP> <2364@amdahl.UUCP>
Organization: USAMC ALMSA, St. Louis, MO
Lines: 49

I'm sure we can all agree that there may be difficulties in using
shuttle External Tanks (ETs) in building a space station. However, I'm
also sure that we can all agree that there MAY be a use for them later
in the space station construction project. Some possibilities (general
storage, air or fuel storage, garden space, privacy areas, etc.) have
already been suggested on the net. 

In any case, right now we are taking them to a certain point, and then
discarding them back to burn up in the atmosphere. To stop doing this may
cost something in shuttle payloads, or save something in fuel usage
(I've seen both views expressed here). I think the problem is that, if
the ETs are taken up to LEO, and just left there, their orbits will
decay relatively rapidly, and they will burn up and be lost anyway (plus
we'll have the old "Skylab-is-falling" bad PR of space debris falling
back in random locations).

So, what will it cost (in terms of impact on current missions,
development and implementation costs, etc.) to arrange for all future
ETs to be carried up to LEO and then put into some higher "parking"
orbit, where they can orbit eternally out of everyones' way until
someone decides they want one? Thus they can be stored for eventual use
if and when they are needed. I would think that this would be the best
course. It keeps open the greatest possible number of options, and I
would think that the incremental cost to do this would be roughly the
cost of one PAM or equivalent per shuttle launch, plus some amortized
engineering costs. This is trivial in comparison to the costs at some
future time to boost into orbit enough raw material or prefab assemblies
to create enclosed space equivalent to the volume of an ET.

When the future space station operators need an ET-sized space, all
they'll have to do is send up the inter-orbit transfer vehicle to the
"parking lot" where the ETs are orbiting, and give one a shove in the
right direction and time so that it sprials down to the station's orbit
at a convenient moment. Minimal cost, no need to bother the groundhogs, etc.

After all, mass in orbit is like money in the bank -- if you've got it
there, you can always get it out, and it can be left indefinitely for
future use, even if now you can't figure out what good it might be. If
it is not there, it will cost you to get some in there. Why throw away
what we already [almost] have by discarding ETs any longer? Up till now,
shuttle flights have really been more like experiments than operations,
so I can't fault NASA for not complicating things by trying to do this
too. But, as shuttle flights become routine business, lets get this
built in as a side benefit, as long as it can be done reasonably.

Regards,
Will Martin

UUCP/USENET: seismo!brl-bmd!wmartin   or   ARPA/MILNET: wmartin@almsa-1.ARPA