OTA@S1-A.ARPA (08/01/84)
From: Ted Anderson <OTA@S1-A.ARPA> Date: 31 Jul 84 0243 PDT From: Ron Goldman <ARG@SU-AI.ARPA> 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 *************** ------------------------------ End of SPACE Digest *******************
OTA@S1-A.ARPA (08/03/84)
From: Ted Anderson <OTA@S1-A.ARPA>
Date: 2 Aug 1984 8:49-PDT From: dietz%USC-CSE@ECLA To:
redford@shorty cc: space@MIT-MC.ARPA Subject: Re: How Does
Geostar Work?
Geostar works by triangulation. A signal addressed to a portable
tranceiver is sent from the central ground station via one of the
satellites. The ground unit then emits a very short
omnidirectional microwave pulse (with ID information included).
All four satellites receive this pulse, and transmit it back to
the ground station. Time delays are used to compute position.
The position is then transmitted back to the ground unit.
The Geostar ground unit is simply a microwave tranceiver capable
of emitting high power (500 watts, I believe) short duration
pulses, along with some fast control logic to detect when the
unit is being polled and to receive and display position
information. Average power consumption is low, because the
pulses are so short (a microsecond?).
The Navstar system uses passive ground units, since they must
operate in combat conditions where radio silence is critical.
These passive units must do the triangulation themselves, so they
are expensive.
Paul Dietz dietz%usc-cse@usc-ecl
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Date: 2 Aug 1984 14:41:29-EDT From: Hank.Walker at CMU-CS-UNH
Subject: tethered satellite stories
A recent one is "Tank-Farm Dynamo" by David Brin in the November
1983 Analog. A space station is created out of two groups of
shuttle external tanks connected together by cables. Shuttles
take advantage of the fact that the lower platform is moving
slower than orbital velocity by "landing" on it and transfering
their payload. The dynamo effect of a cable moving through
magnetic fields is used to pump energy into the stations orbit to
compensate for atmospheric drag.
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Date: Thu, 2 Aug 84 10:51:41 pdt From: David Smith
<dsmith%hp-labs.csnet@csnet-relay.arpa> Message-Id:
<8408021751.AA01896@HP-MARS> To: space%mc@csnet-relay.arpa
Subject: Apollo 2-6 Cc: dsmith@csnet-relay.arpa Source-Info: From
(or Sender) name not authenticated.
The spacecraft which burned on the pad was known as Apollo 204
for some reason. I think (but am not at all sure) it was also
counted as Apollo 4. One unmanned Apollo was lofted into a high
suborbital trajectory, then rammed into the atmosphere at 25000
mph to test the heat shield.
David Smith dsmith%hp-labs@csnet-relay
...!ucbvax!hplabs!dsmith Formerly at Cmu-cs-ius.arpa
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End of SPACE Digest *******************