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Date: Tue, 31-Jul-84 19:58:00 EDT
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Posted: Tue Jul 31 19:58:00 1984
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From:  Ted Anderson 


Date: 31 Jul 84 0243 PDT From: Ron Goldman 
Subject: tethered satellite To: space@MIT-MC.ARPA

n129 0015 31 Jul 84 BC-TETHER (ScienceTimes) By WALTER SULLIVAN
c. 1984 N.Y.  Times News Service NEW YORK - The ''skyhook,'' a
concept with deep roots in history, is still alive in the minds
of men.  ''Let us build us a city and a tower, whose top may
reach into heaven,'' said the descendents of Noah, according to
the Book of Genesis.  But to thwart such an impious project the
Lord confused the builders with a multitude of languages and the
Tower of Babel was never built.  The idea of a tower that, in a
sense, reached to heaven was revived in a series of proposals,
beginning in 1895, for the building of cable-car systems or other
''highways'' into space.  Their direct descendent is a scheme of
the National Aeronautics and Space Administration for a satellite
tethered to a space shuttle by a 60-mile cable.  It was in 1895
that Konstantin E. Tsiolkovsky, the original Russian dreamer of
space travel, proposed building a tower on the Equator that would
reach beyond geostationary altitude.  At the geostationary
height, 22,300 miles above the earth, the motion of an object in
a west-to-east orbit keeps pace with the earth's rotation.  It
therefore remains stationary relative to features on the earth
beneath it.  While gravity would pull on that part of a tower's
structure below that elevation, the stress could be compensated
by centrifugal force of the earth's rotation, Tsiolkovsky
reasoned, if the tower were extended beyond geostationary height.
''The point is,'' he wrote of such a tower, ''that the top part
aspires to fly due to the centrifugal force; while the lower part
pulls in the opposite direction.'' In the 1960s there were
several proposals in which the structure, instead of being built
up from the earth, would be suspended from orbiting objects whose
combined center of gravity was at geostationary elevation.  Y.N.
Artsutanov in the Soviet Union, who suggested such an anchor in
space, envisioned it supporting a ''funicular'' or system of
cable cars that would carry payloads into the cosmos.  Six years
later John D. Isaacs of the Scripps Institution of Oceanography
and three colleagues, apparently unaware of the Russian
proposals, published in the journal Science a similar scheme that
they called the ''Skyhook.'' Once cargo passed the geosynchronous
level, they pointed out, the energy of the earth's rotation would
throw it off into space.  This energy, they added, might even be
used to lift the load from the earth's surface.  ''Very large
masses could be slung into space,'' they said.  A Skyhook could
also be used to support a laboratory at the geosynchronous level,
deliver supplies to spacecraft, collect energy or material from
space or support very tall structures on Earth.  The proposal was
published despite doubts by the journal referees as to its
practicalty.  A seemingly insurmountable problem was providing a
cable thousands of miles long, strong enough to carry the load,
yet not so heavy that it would break of its own weight.  Closer
to the planned NASA missions was one for a low-level,
geostationary communications satellite proposed in 1969 in the
Journal of the British Interplanetary Society by A.R.  Collar and
J.W.  Flower.  The satellite would be kept close enough to the
earth for low-power communications by being suspended from a
satellite high enough so the combined gravity of both vehicles
would be at geostationary level.  The first tests of a tethering
scheme were initiated in 1981 by Prof.  James G. Anderson of
Harvard University.  They consisted of lowering an instrument
package as much as 12 miles below a balloon at very high
altitude, then reeling it back up again to obtain data at many
levels of the stratosphere.  The space missions now being planned
call for a space shuttle to deploy a tethered capsule that, with
its own propulsion, will be able to climb higher or descend lower
than the shuttle's own orbit.  This will enable it to make
observations in relatively ''hot'' regions of the Van Allen
radiation belt, above the shuttle orbit, or descend into upper
fringes of the atmosphere where, because of drag, the shuttle
itself could not long remain.  This Tethered Satellite System is
sponsored by the American and Italian space agencies, which have
invited researchers to submit proposals for its first three
flights.  On the first mission it is planned to project the
capsule 12 miles upward with instruments to record the earth's
magnetic field as well as high energy particles magnetically
trapped in the Van Allen radiation belt.  On the next mission, a
year later, it is planned to send the capsule down to make
atmospheric observations.  The third mission would again be above
the shuttle.  As presently planned the capsule will be a
1,000-pound sphere, five feet in diameter, equipped with gas jets
to control its deployment out to 60 miles from the shuttle.  The
tether is a Kevlar cable one-sixteenth of an inch thick that
weighs only 3.56 pounds per mile and has a breaking strength of
650 pounds.  Instruments can be attached to the capsule on long
arms.  On each flight it will be left deployed for about 16 hours
before being reeled in.  The project was devised by two Italians
associated with the Smithsonian Astrophysical Observatory in
Cambridge, Mass., Mario D. Grossi and the late Giuseppe Columbo.
Last summer about 150 specialists from government, industry and
academia conducted a workshop on applications of tethered
satellites and the findings have been summarized in a NASA
memorandum by Georg von Tiesenhausen of the Marshall Space Flight
Center in Huntsville, Ala.  nyt-07-31-84 0313edt ***************

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End of SPACE Digest *******************