Can electrodynamic tether propulsion use the solar magnetic field?

Question

Electrodynamic tethers have been proposed for satellite propulsion in the magnetic fields of Earth and the Gas Giant planets.

Is it realistic to consider using the Sun's magnetic field for electrodynamic propulsion in the inner solar system? The Sun's magnetic field is stronger than Jupiter’s, and the solar wind is electrically conductive https://en.wikipedia.org/wiki/Interplanetary_magnetic_field so the two primary requirements for electromagnetic tether propulsion are met.

Magnetic field strength increase closer to the Sun. The interplanetary magnetic field strength is much too low at 1AU (almost an order of magnitude less than Earth LEO). But the solar field strength at the Sun's poles is more than an order of magnitude greater than Earth's. At some distance inside 1AU, the interplanetary magnetic field strength must be equal to or greater than Earth's.

At what orbital radius is electrodynamic tether propulsion realistic? A solar powered, tether-propelled spacecraft could potentially perform long term, propellant-free missions in this zone.

Answer 1

Some figures I found suggest that 300km above the earth would have a strength around 0.24 gauss (Research India), while the interplanetary field at 1AU is only about 50 micro gauss (Valee). I suspect that it would be very difficult to make use of a field that weak.

Answer 2

There’s no definition of “practical” except in some context.

Mission proposals exist using IMF tethers, given the parameters of 1) long-enough tethers, of good enough properties, and 2) light-enough spacecraft, reducing the demand on the forces needed. In turn, 2) implies mission schedules work out, which itself implies trajectory design works out to something usable.

The specific proposal I saw was for a fleet of ~3U cubesats, each taking X years to reach a target using a tether of Y length. Given the mass of a 3U, and X, (and of course the observed field strength,) length Y was certainly long, but no longer than a hundred other proposed tethers. All told, the proposal was no wackier than a hundred other tether-based concepts.

Change the parameters to a human capsule, going a significant distance, within however many days to weeks, and the proposal goes wacky. The tether length necessary will exceed any human construct.

Answer 3

in NASA’s “Tethers In Space Handbook” p42 https://ntrs.nasa.gov/api/citations/19920010006/downloads/19920010006.pdf is a discussion of a "Heliocentric Alfven Engine for Interplanetary Transportation" It considers generation of propulsion for interplanetary travel by using the electromagnetic interaction of a superconducting tether and the interplanetary magnetic field.

This system could be used to spiral away from or toward the sun, or to move out of the ecliptic. Theoretically, such a spacecraft could attain the solar wind velocity of 400 km/sec. Use of the electromagnetic interaction between a conducting tether system and the solar wind may allow much shorter transfer times and larger payloads for planetary missions.

The proposal considers the use of a 1000km length wire tether which would produce 2MW.

More detailed study and evaluation of this application are required