Aucbvax.5438
fa.space
utzoo!decvax!ucbvax!space
Fri Dec 11 03:37:00 1981
SPACE Digest V2 #56
>From OTA@S1-A Fri Dec 11 03:28:28 1981
SPACE Digest Volume 2 : Issue 56
Today's Topics:
Shuttle's wings
Shuttle's and laser launching system
laser launching systems
Meteor showers
Penthouse, please..
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Date: 10 December 1981 1040-EST (Thursday)
From: David.Smith at CMU-10A (C410DS30)
To: space at mit-mc
Subject: Shuttle's wings
Message-Id: <10DEC81 DS30@CMU-10A 104051>
The shuttle's wings are as big as they are because the Air Force won
the argument with NASA. The AF wanted the ability to fly up to
1,000 miles cross-range on reentry. This is needed in the event that
a shuttle launched into a polar orbit from Vandenberg has to come
down after one orbit.
------------------------------
From: BRUC@MIT-ML
Date: 12/10/81 11:12:09
Subject: Shuttle's and laser launching system
BRUC@MIT-ML 12/10/81 11:12:09 Re: Shuttle's and laser launching system
To: Space-Enthusiasts at MIT-MC
First, the research on the laser launching system was done by
Avco Everett Research Labs. I've asked them for a report, and if and
when I get it, I will report some of its results here.
Next, I don't know too many technical details of the system,
but Dr. Kantrowitz did mention a few. The system they were designing
would have put a one ton capsule into orbit (at 10 g's). It would have
required a one gigawatt (average power input) laser. Currently, the
unclassified record is two megawatts (probably average power output).
In any event, getting something that big would require many lasers
operating in parallel. The cost of operating the system is that of the
power plus whatever maintenence. At 10 g, orbit is achieved in about 90
seconds, so the system requires 25000 kwh per ton in orbit. At 10
cents/kwh, that's $2500.
As far the politics of developing the shuttle went, NASA's
decision to go with the shuttle at the time was OK. Laser technology
was nowhere near the levels it's at now. Mass drivers would have
plausible. Ditto for the big dump booster idea. It's understandable
why they didn't pursue any more esoteric system, but that doesn't make
it any less of a shame. Avco isn't working on the laser launch system
anymore, and they should be. The research should still be happening,
but the threat it poses to the shuttle via the powerful critics of the
shuttle is still signifigant. I suppose that once the shuttle is
operational and in heavy demand, we can really start pursuing all
these launch systems energetically. But then, there probably won't be
any money for research on advanced designs (OMB is trying to cut all
such research from NASA's budget.)
------------------------------
Date: 10 Dec 1981 1158-CST
From: Jonathan Slocum <LRC.SLOCUM AT UTEXAS-20>
Subject: laser launching systems
To: space at MIT-MC
It occurs to me that a laser launching system can be considered to be
just another use of a high-power laser weapon, in that the operational
characteristics are essentially identical. Rather than melting the
skin of the vehicle, of course, one hopes to heat/vaporize some
substance that exhausts at a high velocity. But there are some very
serious problems with this approach. To quote from the most recent
issue of High Technology (v. 1, no. 2, Nov/Dec 1981, pp. 79-80):
As the evidence indicates, there's no consensus of opinion
on the feasibility of laser weapons. The technological issues
are complex and far from settled, and they present a major
challenge for scientists and engineers. Building a large enough
laser, while by no means a trivial task, is probably the easiest
step; even such pessimists as Tsipis [MIT] and Callaham [CMU]
concede that high laser powers appear to be attainable. The
most serious problems arise in reliably directing high powers
onto a small enough area of a distant, moving target for a long
enough time to do lethal damage.
The atmosphere presents a complex set of problems. Although it
looks transparent, the atmosphere isn't transparent enough for
high-energy lasers. Even clear air absorbs a tiny fraction of
the light going through it, and any absorption at all can be a
serious source of trouble when trying to transmit millions of
watts of light. That slight absorption is enough to heat the
air a little, and as the air is heated it expands, reducing its
density. As density decreases, the refractive index of the air
in the beam path decreases, in effect making the air into a negative
lens, spreading out the beam -- an effect called "thermal blooming."
Atmospheric turbulence and a variety of other effects can also make
laser beams wander off their targets.
The next paragraph goes on about focussing problems (insuring sufficient
energy presence/density at the target) which arise even in space. A
recent Sci. Am. article dwells on the focussing/tracking issues, which
are a source of some controversy. But the big, perhaps insurmountable
problem for earth launches would appear to be atmospheric distortion.
Unless the atmosphere is darn-near 100% transparent at some wavelength
for which we can induce a substance to lase at extraordinary power levels,
or we can find a way to make and sustain large tubular holes in the air,
it ain't-a-gonna-work!
------------------------------
Date: 9 Dec 1981 2039-EST
From: G.RONNIE at MIT-EECS at MIT-AI
Subject: Meteor showers
To: ota at S1-A
Has there been some kind of meteor shower going on in the past 3 or
4 weeks? I ask because during this time I have seen an excess of
meteors shooting across the sky.
------------------------------
Date: 10 Dec 1981 18:51 PST
From: Wedekind.ES at PARC-MAXC
Subject: Penthouse, please..
To: Space-Enthusiasts at MIT-MC
cc: Wedekind.es
I think it was OMNI where I saw the space elevator idea; they would run on
cables which are anchored on the equator and extend somewhat past the
geosynchronous orbit (22,000 miles?), where there is a big weight tied at
the end to keep them stretched tight.
If I remembered that much right, a few picky technical problems come to
mind. The first is that it requires very strong cables - able to support
at least 3,000 miles of their sea level weight by my calculations.
I don't remember if the OMNI article was presented as speculative science
or out-and-out fiction; does the idea seem ridiculous now, ridiculous for
the near future, or just forevermore ridiculous?
Jerry
------------------------------
End of SPACE Digest
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