ARG@SU-AI.ARPA (07/31/84)
From: Ron Goldman <ARG@SU-AI.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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