Tether radiation in Juno-type and circular-equatorial Jovian orbits

Abstract

Wave radiation by a conductor carrying a steady current in both a polar, highly eccentric, low perijove orbit, as in NASA's planned Juno mission, and an equatorial low Jovian orbit (LJO) mission below the intense radiation belts, is considered. Both missions will need electric power generation for scientific instruments and communication systems. Tethers generate power more efficiently than solar panels or radioisotope power systems (RPS). The radiation impedance is required to determine the current in the overall tether circuit. In a cold plasma model, radiation occurs mainly in the Alfvén and fast magnetosonic modes, exhibiting a large refraction index. The radiation impedance of insulated tethers is determined for both modes and either mission. Unlike the Earth ionospheric case, the low‐density, highly magnetized Jovian plasma makes the electron gyrofrequency much larger than the plasma frequency; this substantially modifies the power spectrum for either mode by increasing the Alfvén velocity. Finally, an estimation of the radiation impedance of bare tethers is considered. In LJO, a spacecraft orbiting in a slow downward spiral under the radiation belts would allow determining magnetic field structure and atmospheric composition for understanding the formation, evolution, and structure of Jupiter. Additionally, if the cathodic contactor is switched off, a tether floats electrically, allowing e‐beam emission that generate auroras. On/off switching produces bias/current pulses and signal emission, which might be used for Jovian plasma diagnostics.

Comparative Saturn‐Versus‐Jupiter Tether Operation

“…At Jupiter, tethers could be effective because its field B is high (Sanmartin et al, ). Tethers would allow a variety of science applications (Sanchez‐Torres & Sanmartin, ). The Saturn field is 20 times smaller, however, and tether operation involves field B twice , which makes that thermodynamic character manifest: The S/C velocity v ′ relative to the corotating magnetized planetary plasma induces in it a motional electric field E m = v ′ ∧ B , in the S/C reference frame, a Faraday effect in XIX‐century language, previous to Relativity. The field B exerts Lorentz drag per unit length I ∧ B on tether current I driven by E m . …”

“…At Jupiter, tethers could be effective because its field B is high (Sanmartin et al, 2008). Tethers would allow a variety of science applications (Sanchez-Torres & Sanmartin, 2011). The Saturn field is 20 times smaller, however, and tether operation involves field B twice, which makes that thermodynamic character manifest:…”

Electrodynamic Tethers For Planetary And De-orbiting Missions

“…In Ref. [90] we carried out a broader analysis of the radiation impedance of a tether, considering both Alfven and FM modes and a range conditions: characteristic arc of two Juno-like orbits, and a prograde or retrograde Low Jovian Orbit (LJO). In all cases, the Alfven velocity is large when compared to the LEO case, because of the low dense, highly-magnetized Jovian plasma; this results in a much larger Alfven impedance.…”