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>From OTA@S1-A Sat Dec 19 03:27:44 1981

SPACE Digest                                      Volume 2 : Issue 64

Today's Topics:
				 Skyhooks
	Nuclear Power Plant vs. SPS for Laser Launch System Power
			      Laser launches
				Spaceports
				Spaceports
			       Momentum   
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Date:  18 December 1981 18:05 est
From:  Tavares.Multics at MIT-Multics
Subject:  Skyhooks
To:  Space-Enthusiasts at MIT-MC
In-Reply-To:  Message of 18 December 1981 06:03 est from Ted Anderson

I assume you're suggesting building a hollow pyramidal skyhook, 200
meters wide at the base and meeting at the point?  It seems to me that
this would ADD strain to the structure.  For instance, small to
medium-size radio towers come to a point at the bottom just so wind
flexing won't tear them apart.  I should think that the magnitude of
possible side forces on a skyhook structure would be much worse.

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Date: 18 Dec 1981 17:39:41-PST
From: A.exp at Berkeley
Subject:  Nuclear Power Plant vs. SPS for Laser Launch System Power

I don't like radiation.  Why not use an laser SPS instead of the
nuclear power plant for the laser-launched shuttle?  The power could
be beamed to Earth and stored, then fired from Earth based lasers
during the first part of launch to reduce thermal bloom while the shuttle
is still deep in the atmosphere.  After the shuttle gets out of the atmosphere
it could be illuminated directly by the laser on the SPS, saving storage
costs on the ground and allowing you to get away with fewer lasers on the
ground since the reduced ground cost would allow decreased efficiency 
during part of the boost.

If only ground-based lasers are used, the thermal bloom must be fought
even after the shuttle itself clears the atmosphere, but for an SPS
laser, after the shuttle gets through the denser layers there is a
corresponding reduction in the thermal bloom effect, so you would need
only one laser on it.  Also note that nuclear power plants have had
the problem that they are out of commission .2 to .5 of the time.

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Date: 19 Dec 1981 00:47:53-EST
From: dee at CCA-UNIX (Donald Eastlake)
To: space at mc
Subject: Laser launches

If you need a lot of power for just 90 seconds, can't you accumulate it in
flywheels or something over a longer period of time??  (Maybe a flywheel
at each of multiple lasers?)

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Date: 19 December 1981 03:10-EST
From: Robert Elton Maas <REM at MIT-MC>
Subject: Spaceports
To: Hans Moravec at CMU-10A
cc: SPACE at MIT-MC

Even if the mass and complexity of the 600 km linear accellerator is
the same as the rotating&dipping cable in orbit, the l.a. is much
easier to build. Why? (1) It can be built and tested incrementaly.
Each piece can be installed in sequence and suborbital test flights
of cheap passive material (dirt, rock) can be made. When enough
sections are installed to achieve orbital velocity, it becomes
operational. The dipping cable, on the other hand, must be built
and installed as one big piece somehow. (2) The cable must be put
into space somehow whereas the linear accellerator can be installed
by conventional means such as bulldozers cranes trucks etc. Thus
the linear accellerator can be started now without needing the
shuttle whereas the dipping cable will DETRACT from shuttle payload
capacity by diverting capacity from normal use to cable use, and can't
be started anyway until the shuttle is operational. Thus I don't
think the cable should be done until after we are well out into
space, whereas unemployed construction workers could be assigned
to the accellerator in 1982. We could use the shuttle for delicate
equipment and people, and the linear accellerator for bulk materials.
(I'm not sure whether we should do the Earth-based accellerator now
and use it for bootstrapping ourselves into space industry, or
go instead with the moon-based accellerator which WILL need a
few shuttle payloads to get it installed but possibly be more
effective due to lower moon gravity and lack of atmospheric friction.)

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Date: 19 December 1981 04:22-EST
From: Jerry E. Pournelle <POURNE at MIT-MC>
Subject: Spaceports
To: Hans Moravec at CMU-10A
cc: SPACE at MIT-MC

Galombos proposes a spaceport, cnsisting of a large mass in high
orbit that can lower a cable about 400 km long; hook onto a
suborbital mass at Shuttle; and up it goes. The energy in the
spaceport is restored by ion engines and solar arrays.

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Date: 19 December 1981 04:25-EST
From: Jerry E. Pournelle <POURNE at MIT-MC>
Subject: Momentum   
To: HPM at S1-A
cc: SPACE at MIT-MC

AHA! You want to use Earth's rotational energy for space
launches. YUou technologists never care about the environment at
all.  What about all the creatures that can't survive longer
days and nights?

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End of SPACE Digest
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