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Aviation History
1988
1988 - 1859.PDF
E rr Shut / .. . .•• .,. apsule / CB / \ lliilltflll8 li V TSi :f:': ^sagr. re-entry is induced by atmospheric drag after release into the upper atmosphere. Another tether application could be orbital transfer, deploying a satellite from Shuttle into a high orbit without the use of a rocket motor. With the tether extended, the Shuttle would be below the system's e.g. Momentum from the Shuttle is transferred to the plat form or satellite at the tether's end, which is above the e.g., and when the satellite is released its higher-than-normal momentum boosts it into a higher orbit. At the same time, the Shuttle's lower-than-normal momentum will lower its orbit, which could assist its return to Earth without the use of the orbital manoeuvring system. The active control of a moveable attach ment point of a tethered body is a new method of attitude control. This could be used for the high-precision pointing of a science and applications platform tethered to a Space Station. The Shuttle might be used to deploy a small TSS, appropriately instru mented with an attitude measurement and control system, to achieve tens of arcseconds performance. Aeritalia says that the goal of such a flight would be the measurement of attitude dynamics with and without attitude control, the measurement of attitude stabilisation in response to induced dynamic disturbances, and the measurement of displacement mech anism and control system performance. A proposed Shuttle mission would use a tethered Spartan free-flier. Test-mission results could lead to the deployment of a telescope from Space Station. A ten-ton plat form has already been designed, carrying a five-ton payload, a power line supplying 15kW, and an optical-fibre link, carrying data at 20 megabytes per second. Gravity gradiency provides a tethered system self-orientation along the local verti cal. This feature could be used to maintain the correct orientation of structures being erected in space, which tend to be unstable during assembly. Passive control may be achieved by attaching one or more tethers with end masses for ballast. A tethered system, using an electro magnetic tether, could provide the basis for an orbiting long antenna to generate ULF/ELF/VLF waves for worldwide communications. Aeritalia says that a giant loop antenna could result from "electrons from the ionosphere spiralling along magnetic field lines and being attracted by the electron collector at the end of the tether. The electrons move down the tether and are shot back into space from an electron gun on Tethered Satellite could be used to control the re-entry of recoverable capsules Shuttle. They then spiral along magnetic field lines back into the ionosphere, closing the current loop. "The antenna generates electromagnetic waves into which messages can be incorpo rated by modulation, for example, by switch ing the electron gun on and off at the desired frequency. Theoretically, these waves may be spread quickly over the globe by a process called ducting." A Shuttle demonstration flight would use a 20km to lOOkm-long tether with a 10A tether current. This would inject about 1W by night and 0-1W by day into the transmission line. By stringing several instrumented probes along a tether, deployed towards the Earth from a spacecraft, it is possible to study the atmosphere at different levels, with good time correlation of measurements. This one- dimensional constellation could be valuable for low-altitude studies, and when data has to be collected simultaneously in different atmospheric regions. A Shuttle demonstra tion flight would use a TSS with five probes attached to the tether, and able to crawl along it. Aeritalia has suggested a "getaway tether" service, in which small tethered systems would be deployed from the Shuttle's Getaway Special compartments to conduct basic and low-cost experiments. A system could comprise a 20kg upper mass and a 50kg lower mass, connected by a one- kilometre tether. An experiment, called Gate, is already being designed to evaluate electrodynamic thrust and power generation. Looking further into the future, Aeritalia has proposed several advanced applications, one of which uses tethers and spent Shuttle external tanks. The tanks would be latched together like a raft, and two rafts would be connected by a tether system. This would act as spaceport, or as an anchor for tether experiments into astrophysics, for example. Multiple tethered systems could be used to enhance the Space Station, providing orbital transfer vehicle (OTV) hangar refuelling facilities, momentum release of an OTV, and retrieval of the OTV, as well as a 50-ton science platform trawled beneath the Station: A space elevator would provide for micro- gravity experiments, re-entry, tether inspection, and repair. Further afield, a proposed Mars aeronomy mission would deploy an aerodynamically- designed tethered satellite to conduct low- level measurements of the planet's atmos phere. Similar missions could be performed on the Moon and planets. „ FLIGHT INTERNATIONAL, 16 July 1988 37
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