Spaceborne long vertical wire as a self-powered ULF/ELF radiator

In December 1987, on the occasion of the first demonstration flight of the shuttle-borne Tethered Satellite System (T.S.S.), NASA will deploy in orbit a 20-km vertical conducting wire (electrodynamic tether) and will test, among other things, the wire\´s ability to function as generator of de electric power, through the mechanism of interaction, as well as its capability to operate as a serf-powered radiator of ultra-low frequency/ extremely low frequency waves (ULF/ELF), through such mechanisms as the Alfvén Wings. The wire\´s ability to generate dc electric power up to the 100 kW level has been investigated by several authors and it is now considered to be a reasonable expectation. Concerning the wire\´s ability to radiate ULF/ELF waves, rigorous analytical evidence still has to be worked out. The expectation at this time is that this vertical radiator may be able to inject from above into the earth-ionosphere transmission line about 10 W at night and by day. Thus in the "hot spot" on the earth\´s surface, directly underneath (in a magneto-conjugate sense) the orbiting system, signal-to-noise ratios of practical interest may be achievable against natural micropulsation noise. The tether\´s ability to excite from above long-range propagation modes in the earth-ionosphere transmission line has still to be verified analytically. It is expected that by 1987-1989, comprehensively analytical and experimental evidence will be available to the ULF/ELF community, so that conclusions may be drawn as to the feasibility of strategic communications using orbiting wires. The advantage of the spaceborne placement for the ULF/ELF radiator, compared with the traditional ground-based placement, may be the avoidance of the potential environmental threat posed by the conventional siting.