Artificial auroral effects from a bare conducting tether

Abstract

Abstract. An electrically floating metallic bare tether in a low Earth orbit would be highly negative with respect to the ambient plasma over most of its length, and would be bombarded by ambient ions. This would liberate secondary electrons, which, after acceleration through the same voltage, would form a magnetically guided two-sided planar e beam, and result in auroral effects (ionization and light emission) upon impact on the atmospheric E layer, at about 120-140 km altitude. This paper examines in a preliminary way the feasibili.ty of using this effect as an upper atmospheric probe. Ionization rates can reach up to 105 cm '3 s '• if a tape, instead of a wire, is used as tether. Contrary to standard e beams, the beam from the tether is free of spacecraft charging and plasma interaction problems, and its energy flux varies across the cross section, which is quite large; this would make possible continuous observation from the satellite, with high resolution, both spectral and vertical, of the induced optical emissions. Ground observation might be possible at latitudes around 40 ø , for night, magnetically quiet conditions.

The orbital-motion-limited regime of cylindrical Langmuir probes

“…If conductive, its electrodynamic interaction with the ionosphere and geomagnetic field has potential applications that range from power generation and propulsion 1 to the use of wave 2,3 and particle emissions. 4 The standard tether carries insulation, and has end devices to establish and control electrical contact with the ionospheric plasma. The bottleneck for such applications is the efficient capture of ionospheric electrons at the anodic end of the tether: the electron gyroradius and Debye length are so small compared to any useful, threedimensional, passive anode that both magnetic guiding and electric shielding greatly reduce collection.…”

Analysis of Tether-Mission Concept for Multiple Flybys of Moon Europa

“…With hollow cathodes off during each flyby, the tether will be electrically floating [8], attracting ions over most of its length. This results in a continuous beam of energetic secondary-emission electrons, with their energy and flux increasing with distance from the anodic tether end, allowing for auroral effects to probe the Jovian ionosphere [16]. Some characteristic mission values are given in the Table 1.…”

“…A total eccentricity decrement Ae T «-0. 16 is required to reach the Ganymede apojove at e = 0.86 from e h « 1.02. The eccentricity decrement perperijove pass proves nearly independent of both radius r" and e value before each pass (for e > 0.5, suppose); the dose per orbit proves similarly near independent of eccentricity and perijove radius if near Jupiter, with the number of perijove passes thus being a metric for the total dose [8].…”

A review of electrodynamic tethers for science applications

“…The low ion current makes for no ohmic effects, bias increasing linearly with distance d from the top at the E m rate. Ambient ions impacting the tape both leave as neutrals and liberate additional secondary electrons, which race down the magnetic field and excite neutral molecules in the E-layer, resulting in auroral emissions [18].…”

“…An iterative solution scheme uses density values at a step in evaluating a 10 3 x 10 3 linearized kernel matrix, to determine densities at the next step. Proceeding with inversion requires a regularization technique; a direct approximation to the actual density profile used as good initial guess to start the iteration, which would not converge otherwise, is first obtained by fitting parameters in a model and using a Direction Set (Powell) technique [18].…”