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

Abstract

All four giant planets, far from the Earth and sun and having deep gravitational wells, present propulsion and power mission issues, but they also have an ambient plasma and magnetic field that allows for a common mission concept Electrodynamic tethers can provide propellantless drag for planetary capture and operation down the gravitational well, and they can generate power to use along with or be stored for inverting tether current The design for an alternative to NASA's proposed Europa mission is presented here. The operation requires the spacecraft to pass repeatedly near Jupiter, for greater plasma density and magnetic field, raising a radiation-dose issue that past analyses did take into account; tape tethers tens of kilometers long and tens of micrometers thick, for greater operation efficiency, are considered. This might result, however, in attracted electrons reaching the tape with a penetration range that exceeds tape thickness, thereby escaping collection. The mission design requires keeping the range below thickness throughout, resulting in an orbit perijove only hundreds of kilometers above Jupiter and tapes a few kilometers long. A somewhat similar mission design might apply to other giant outer planets. Copies of this paper may be made for personal and internal use, on condition that the copier pay the per-copy fee to the Copyright Clearance Center (CCC). All requests for copying and permission to reprint should be submitted to CCC at www.copyright.com; employ the ISSN 0748-4658 (print) or 1533-3876 (online) to initiate your request.*

Comparative Saturn‐Versus‐Jupiter Tether Operation

“…Saturn and Jupiter operations present an important difference involving i av and the issues raised in (Sanmartin et al, ). Consider how maximum tether point temperature varies with L and B (Sanmartin et al, ), …”

“…Planetary capture is more effective ( S/C ‐ to‐tether mass ratio M SC / m t is higher), the thinner and longer a tape, and the lower the incoming S/C periapsis, B dipole value decaying very rapidly with distance to the planet. But Jovian tethers cannot operate at extreme optimal conditions because of the very high B value itself, which might lead to strong tether heating and to electrons crossing the tape with penetration range greater than thickness h , escaping collection; maximum mass ratio for effective capture by Jupiter might only reach to about 3.5 (Sanmartin et al, ).…”

“…All Giant Outer planets have magnetic field B and corotating plasma, allowing nonconventional exploration. Electrodynamic tethers, which are thermodynamic (dissipative) in character, can 1. provide propellantless drag both for deorbiting spacecraft in Low Earth Orbit at end of mission and for planetary spacecraft capture and operation down the gravitational well, and 2. generate accompanying, useful electrical power, or store it to later invert tether current (Sanmartin et al, 1993;Sanmartin & Estes, 1999).…”

Tether capture of spacecraft at Neptune

“…A disruptive bare-tether concept enhanced current flow by eliminating tether insulation and a large spherical conductor at the anodic end [4], making current and relative plasma-bias vary along the tether -causing it to act as a giant Langmuir probe. Design capture-efficiency requirements for Jupiter are less than expected because its high B value might result in strong tether heating and/or energetic attracted electrons crossing the thin-tape tether and missing collection [5]. This requires limiting tether length L t -to keep length-averaged current density well below a maximum: short-circuit value σ t E m (σ t being tether conductivity)-due to ohmic effects and proportional to field B.…”

Planetary exploration of Saturn moons Enceladus and Dione

“…Following capture by Saturn, repeated Lorentz force around periapsis may bring the apoapsis first to an elliptical orbit at 1:1 resonance with Dione. After a number of flybys, with its Hollow Cathode off to explore Dione, as had been suggested for a minor tether mission to moon Europa [7], repeated tether operation might bring the apoapsis down to reach a resonance with Enceladus, for parallel flybys. Section 4 shows that Lorentz-drag peaking at periapsis greatly simplifies the analysis, and tether operation in touring Enceladus and Dione is explicitly determined.…”