Aucbvax.5481
fa.space
utzoo!decvax!ucbvax!space
Tue Dec 15 04:10:29 1981
SPACE Digest V2 #60
>From OTA@S1-A Tue Dec 15 04:01:46 1981
To: SPACE@MIT-MC
Reply-To: Space-Enthusiasts at MIT-MC
SPACE Digest Volume 2 : Issue 60
Today's Topics:
Laser launch systems
Sub Orbital Launch
Skyhook Stability
Linear accelerators as launchers.
interest rates & launching lasers
specific thrust of materials
Cables in space
the Gap
interest rates & launching lasers
Elevators, fuel
Ultimate limits
Shuttle's wings
Shuttle's and laser launching system
laser launching systems
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Date: 14 Dec 1981 0724-PST
From: Jim McGrath <JPM SU-AI AT>
Subject: Laser launch systems
To: space at MIT-MC
Although there does seem to be some similar points between laser weapons
and a launch system, the launch system is far more practical. Certain
advantages are as follows:
1) Launch from a high elevation. This decreases fuel costs but, more
importantly, decreases the amount of atmosphere you have to punch
through.
2) Launch in good, calm, weather. You can take your time when launching,
just as shipmasters of old did. Keep a shuttle in reserve for an
all weather transport.
3) Use several lasers (which can be time-shared between different payloads)
for launching. This reduces the need for a continous beam from a
single laser.
4) Use different pathways for the laser beams. If the beams are firing in
burst mode, then this reduces the effects of blooming considerably.
5) Use a nuclear power plant, selling excess power to the electric grid.
This is actually a far more cost effective idea than most of the
comments so far indicate. For instance, launch only during the
night - that way the power demand curve is evened out, and little
extra costs are incurred. Use the day for repairs. It also gives
you fantastic night launchings if you can see the beam!
The ideal site would be in southern US or Mexico, hooked into a large
power grid, at a high elevation and with clear, calm weather at night.
Any suggestions from folks down thataway?
Jim
PS Note that while I am more confident that the system would work,
I am still not totally convinced. Any document out there with
hard, crunchy, numbers?
------------------------------
Date: 14 Dec 1981 0725-PST
From: Jim McGrath <JPM SU-AI AT>
Subject: Sub Orbital Launch
To: space at MIT-MC
An interesting article appeared in ANALOG magazine a year or so ago
on sub orbital launching. Throw something up into the air at relatively
low speed. In near space it encounters a linear accelerator which
transfers momentum from itself to the payload, placing it in orbit.
The accelerator itself stays in orbit either via ion drive, solar
sails, or momentum transfer from incoming payloads to earth.
Couple this with a laser launch system and you have a more effective
combination. We could do it in a 10-15 year time frame (it all
depends on how big you want the facility). Will we have a beanstalk
by then? Probably not due to the greater materials (in technology and
volume) requirements of the latter - you will need an accelerator in
order to develope space sufficiently in order to let you get anywhere
with skyhooks.
Jim
------------------------------
Date: 14 Dec 1981 0734-PST
From: Jim McGrath <JPM SU-AI AT>
Subject: Skyhook Stability
To: space at MIT-MC
There appear to be large technical problems with skyhook stability due
to two factors. First, the skyhook is vertically unstable. That is,
small displacements will not tend to be corrected. I do not believe there
is a similar horizontial stability problem, but there is another difficulty
due to the fact that a skyhook is a very long and thin structure, with
the primary strength criteria for construction being compression, not
shear. If the structure suffers a horizontial shock, then the energy
will be transmitted as a wave throughout the structure, potentially
causing a lot of damage.
First, are my fears grounded? Second, can we get materials that have
both compression and shear characteristics we want? Finally, can we
use feedback in order to dampen some of these problems (remember that the
speed of light is a serious limitation here).
Jim
------------------------------
Date: 14 Dec 1981 0741-PST
From: Ted Anderson <OTA AT S1-A>
Subject: Linear accelerators as launchers.
To: space at MIT-MC
CC: jpm at SU-AI
The real problem faced by any linear accelerator used in a orbital launch system
is that all practical lengths lead to rather large accelerations. This is due
to the fact that for a given length (l) and required final velocity (v) the
average acceleration is v^2/2/l. Plugging in some sample numbers we have low
earth orbital speed of 8 km/s, and say our accelerator is 10 km long. This
gives an acceleration of 320g. This is unacceptably high for people and other
relatively fragile cargo. Note that the laser scheme mentioned recently had
and acceleration of 10g for 90 seconds. This gives a length of 400 km. This
still causes soem problems but you don't have to build a track thats 400 km
long.
Ted Anderson
------------------------------
Date: 14 December 1981 1144-cst
From: Bill Vaughan <VAUGHANW AT HI-MULTICS>
Subject: interest rates & launching lasers
To: POURNE at MC, Leavitt at USC-ISI
Cc: SPACE at MC, VaughanW
Whether you set the generator up in Baja or Utah is probably immaterial.
The fact remains that the utility buying your excess power is going to
have to accept a 100% reduction whenever you want to launch a
spacecraft. That means you are not selling that utility any base load;
you are selling peaking power - so the customer will only buy it when it
is needed, not the rest of the time. Your power plant will actually be
producing salable power less than 25% of the time. This will reduce
return on investment substantially.
As far as equity taking the place of interest: this is true only to
the extent you can convince investors that their equity will increase
at a rate greater than the interest rate. (By the way, those investors
are precisely the venture capitalists that Leavitt advocates avoiding.
?? ) It is true that the American investor is a perennial sucker, but
will they go for this? Maybe - if you can produce a convincing (and
nonfraudulent) prospectus.
Anyway, my only point was that financing costs would be greater
than fuel costs. I still think that's true.
------------------------------
Date: 14 Dec 1981 1452-CST
From: Jonathan Slocum <LRC.SLOCUM AT UTEXAS-20>
Subject: specific thrust of materials
To: space at MIT-MC
What Hans neglected to explicate in his reply concerned how one
determines what theoretical thrust is. The basic information is
partly there already, but some dummies like me might not be able to
piece it together. I shall not pretend to be as facile as he is with
the numbers (or the physics) but here is a sketch of the limitations.
Thrust is determined by the velocity and mass of the combustion
products; velocity is determined by (combustion) temperature as well
as the molecular weight of the exhaust products. Therefore, the
higher the temperature, the higher the thrust (in chemical reactions,
of course, the mass is constant). With each fuel/oxidant combination,
one can determine the temperature at which the combustion products
decompose (e.g., water -> hydrogen + oxygen at around 3,000K as I
recall) in an endothermic reaction -- which reduces temperature, hence
exhaust velocity.
As it turns out, hydrogen is the best possible chemical fuel; as an
expert would put it, it has the highest possible "specific thrust"
(probably has something to do with its binding energy, resulting from
chemical reactions within the innermost electronic shell, which Hans
was talking about). Therefore, a hydrogen-burning engine operating at
3,000K is as good as you can possibly get in principle; the Shuttle
engines approach this limit, thus we are near the theoretical limit
w.r.t. chemical engines.
-------
------------------------------
Date: 14 Dec 1981 13:43 PST
From: Wedekind.ES at PARC-MAXC
Subject: Cables in space
To: Hans Moravec at CMU-10A (R110HM60), space at MIT-MC
cc: Wedekind.es
Thanks for a clear explanation of some of the technical issues re space
cables. To reiterate, the figure I gave in my original question for the minimum
characteristic length (~3k mi) of any potential cable material is all wet, because
it assumed no tapering.
I was next going to bring up coriolis forces on the cargo and atmospheric
turbulence but first I better get ejukated.. please tell me what references you
have besides the Clarke and Sheffield books.
Jerry
------------------------------
Date: 14 Dec 1981 1623-PST
From: Stuart McLure Cracraft <MCLURE AT SRI-AI>
Subject: the Gap
To: space at MIT-MC
cc: dist at SRI-UNIX
!n067 1530 14 Dec 81
BC-G(Newhouse 006)
By PATRICK YOUNG
Newhouse News Service
WASHINGTON - Four astronomers think they have found a great cosmic
hole largely devoid of galaxies in a place so far from Earth that
light takes more than 360 million years to bridge the gulf.
The gap itself isn't what has surprised their fellow scientists.
It's the size that has astronomers, cosmologists and astrophysicists
puzzled.
''Since we see large clusters of galaxies, one would expect to see
gaps,'' says David Schramm of the University of Chicago.
The area is some 300 million light-years - roughly 18 quadrillion
miles - in diameter and 180 million light-years deep. (A light-year
is the distance light travels in a year, or about 5.9 trillion miles.)
A gap that big doesn't fit easily into current thinking.
''Existing theories of the distribution of matter in the universe
can't quite explain the discovery,'' says John Huckra of the
Smithsonian Astrophysical Observatory in Cambridge, Mass. ''There is
still some doubt whether it is real.''
But if the gap is real - and new work suggests it is - it should
provide a deeper understanding of how galaxies formed some 1.5
billion years after the birth of the universe. It may even shed some
new light on the Big Bang itself, that gigantic explosion believed to
have begun the universe we know some 10 billion to 20 billion years
ago.
The universe is populated by galaxies, which tend to cluster
together. These galaxy clusters also tend to be grouped into what are
called superclusters. In between are vast regions of space containing
little matter.
''We would like to know how galaxies and galaxy clusters formed,''
says Robert Kirshner of the University of Michigan in Ann Arbor, a
member of the team that discovered the gap.
''At the beginning, we think, everything was homogeneous with matter
evenly distributed. Somehow we have to account for how the structure
of the universe formed. If we understand how this structure grew from
early times to present, we could infer what happened at the
beginning.''
Until now, the largest known gap was about 60 million light-years
across. The new gap appears five times larger, and it takes up far
more space than the largest known supercluster of galaxies.
The new hole was discovered by Kirshner, Augustus Oemler Jr. of Yale
University, Paul L. Schechter of the Kitt Peak National Observatory
in Arizona, and Stephen A. Shectman of the Mt. Wilson and Las
Campanas Observatories in Pasadena, Calif.
The four, using telescopes at Kitt Peak, the Smithsonian's Whipple
Observatory in Arizona and Mt. Palomar in California, were conducting
a survey to determine the distance of galaxies far from Earth. They
were able to observe galaxies up to 40,000 times fainter than the
naked eye can see.
The hole was inferred from three samples of galaxies that formed a
triangle in the area of the constellation Bootes. In each sample, the
gap began about 360 million light-years away and continued outward to
540 million light-years. Preliminary results from more than 100 areas
studied within that triangle has since supported the gap's existence.
Viewed from Earth, the patch of sky appears small. ''If you hold a
garbage can lid up at arm's length, it's that big a piece of the
sky,'' Kirshner says.
But because the region is so far away, the hole actually represents
about 1 percent of the observable universe. Thousands of galaxies
should be found there. Yet the four astronomers find 10 times fewer
than expected.
''To have found a population density of less than three times
average would have been a rare find,'' Schechter says. ''But finding
that the density is about 10 times less than the average is
exceedingly hard to understand.''
The gap intrigues scientists trying to fathom the birth and
evolution of the universe, for it goes to some basic issues in
cosmology. Although matter does clump in galaxies and galaxy
clusters, overall the material of the universe is evenly distributed.
''Two of the most fundamental questions in cosmology today are: Why,
on the large scale, is the universe so smooth; and why, on the small
scale, is it so bumpy,'' Schramm says.
Kirshner and his colleagues continue to investigate whether matter
might exist in the gap in some form other than normal galaxies. Two
unlikely possibilities are as great clouds of gas or as unusually
tiny, faint galaxies, making the gap a ''place where all the galaxies
are pygmies.''
''That in itself would be surprising,'' Kirshner says.
BJ END YOUNG
nyt-12-14-81 1831est
**********
-------
------------------------------
Date: 15 December 1981 03:55-EST
From: Jerry E. Pournelle <POURNE MIT-MC AT>
Subject: interest rates & launching lasers
To: VaughanW at HI-MULTICS
cc: POURNE at MIT-MC, SPACE at MIT-MC, VAUGHANW at MIT-MC,
Leavitt at USC-ISI
It seems clear to me that one could launch on off-hours, or
otherwise schedule to the convenience of customers for power. I
see no reason at all why clever scheduling cannot manage to sell
a lot of power and simultaneously get a lot of stuff into orbit.
Example: an electric furnace steel plant, given the low cost of
labor in certain areas, plus a break on power, might well forgoe
the third shift, leaving one shift for launch and two for
selling power to a steel plant; or, if I can assure you I'll
deliver your power during the hours of 8Am to 8PM, you're likely
to buy; and I'll have 12 for launching.
I fail to understand why we must have a rigidly
scheduled system. Unless, as Alex points out, we can't launch at
night because you can't see where you're going...
------------------------------
Date: 15 December 1981 0410-EST (Tuesday)
From: Hans Moravec at CMU-10A (R110HM60)
To: space at MIT-MC
Subject: Elevators, fuel
CC: Hans Moravec at CMU-10A
Re skyhook stability - The anchored kind is VERY stable vertically -
after it is constructed the bottom end is anchored to the ground,
and the top end (as much as 70,000 miles beyond synchronous orbit)
is ballasted with a counterweight which tries to escape centrifugally,
and puts the entire cable at design tension. When a payload travels
on the part of the cable below synch orbit, its weight (decreasing as
the payload rides up into lower g, higher centrifugal heights) merely
removes some of the load on the anchor - the cable above the load feels
no change in the forces on it, the cable below the payload has its
bias stress temporarily lessened. Coriolis forces are also
no problem - they just cause the cable to lean a tiny bit. Careful
payload scheduling can minimize the long term induced sway.
The cable is so thin for its length that payloads simply thrusting
up and down on it cause no material shear forces to speak of - just
a little local bowing. Unlike a weight on a taught catenary, the
anchored skyhook is a constant tension system. Resonances are another
issue; Pearson's first two papers in the reference list below conclude
that all serious oscillations can be easily avoided. Some ascent/descent
speeds excite resonances, but if you accelerate through those speeds
quickly, the vibrations don't have time to build up.
Re hydrogen/oxygen as the best chemical fuel - actually hydrogen/fluorine
is a little better. The HF reaction product is heaver than the H2O of
the shuttle's engines, but the greater reaction energy more than makes
up for it. Of course both the fuel and the exhaust vapor are very
unpleasant to man and machine - and the reaction is very hot. Still
its one of the major fuels used in high power chemical lasers.
The very highest specific impulse from a chemical reaction undoubtedly
comes from the recombination of atomic hydrogen. H + H -> H2 both
liberates a lot of energy and has a very light, thus high velocity
for the energy, reaction product. Storing the monatomic hydrogen
until it's needed represents a still unsolved packaging problem, however.
Possibly the hypothetical metastable metallic hydrogen is an answer
to this problem too.
Here are the elevator references requested:
Y. Artsutanov, V Kosmos na Elektrovoze (To the Cosmos by Funicular Railway),
Komsomolskaya Pravda, July 31, 1960
(contents described in Lvov, Science 158, p 946, November 17, 1967).
J.D. Isaacs, A.C. Vine, H. Bradner, G.E. Bachus, Satellite Elongation
into a True "Sky-Hook", Science 151 p 682, February 11, 1966 and 152,
p 800, May 6, 1966.
Y. Artsutanov, (The Cosmic Wheel), Znanije-Sile (Knowledge is Power)
No. 7 p 25, 1969.
J. Pearson, The Orbital Tower: A Spacecraft Launcher Using the Earth's
Rotational Energy, Acta Astronautica 2, p 785, September/October 1975.
J. Pearson, Using The Orbital Tower to Launch Earth Escape Payloads Daily,
27'th IAF Congress, Anaheim, Ca., October 1976. AIAA paper IAF 76-123.
J. Pearson, Anchored Lunar Satellites for Cis-Lunar Transportation
and Communication, European Conference on Space Settlements and Space
Industries, London, England, September 20, 1977. in Journal of the
Astronautical Sciences.
H.P. Moravec, A Non-Synchronous Orbital Skyhook, 23rd AIAA
Meeting, The Industrialization of Space, San Francisco, Ca., October
18-20, 1977, also Journal of the Astronautical Sciences 25,
October-December, 1977.
J. Pearson, Lunar Anchored Satellite Test, AIAA/AAS Astrodynamics Conference,
Palo Alto, Ca., August 7-9, 1978, AIAA paper 78-1427.
H.P. Moravec, Skyhook!, L5 News, August 1978.
H.P. Moravec, Cable Cars in the Sky, in The Endless Frontier, Vol. 1,
Jerry Pournelle, ed., Grosset & Dunlap, Ace books, November 1979, pp. 301-322.
R.L. Forward and H.P. Moravec, High Wire Act, Omni, Omni publications
international, New York, July 1981, pp. 44-47.
------------------------------
Date: 15 December 1981 04:56-EST
From: Jerry E. Pournelle <POURNE MIT-MC AT>
Subject: Ultimate limits
To: FONER at MIT-AI
cc: SPACE-ENTHUSIASTS at MIT-MC
Ultimat limits to matter: 42
Reference: Hitchhiker's Guide to the Galaxy...
------------------------------
Date: 15 December 1981 05:05-EST
From: Jerry E. Pournelle <POURNE MIT-MC AT>
Subject: Shuttle's wings
To: David.Smith at CMU-10A
cc: SPACE at MIT-MC
But can't they always land on Easter Island...??
------------------------------
Date: 15 December 1981 05:10-EST
From: Jerry E. Pournelle <POURNE MIT-MC AT>
Subject: Shuttle's and laser launching system
To: BRUC at MIT-ML
cc: SPACE at MIT-MC
Art Kantrowitz is the new Chairman of the L-5 Society and will
be writing on laser launch systems for the L-5 News.
(Subscribe by sending $20 to L-5 1060 E Elm Tucson AZ 85719)
(I don't get paid nothing nohow for L-5 News)
NASA has a decision to make: operate stuff, or develop
advanced technology? There's a conflict. Worth thinking about.
------------------------------
Date: 15 December 1981 05:11-EST
From: Jerry E. Pournelle <POURNE MIT-MC AT>
Subject: laser launching systems
To: LRC.SLOCUM at UTEXAS-20
cc: SPACE at MIT-MC
After all, there are people who believe the Earth is flat; znd I
expect that gunpowder weapons were "controversial" for a long
time, especially amongst experienced pikemen./
You want to be your life on Tsipis, go ahead.
------------------------------
End of SPACE Digest
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