Numerical study of current collection by an orbiting bare tether

An electrodynamic (ED) Tether is a long thin conductive string deployed from a spacecraft. A part of the ED tether near one end is rendered positive with respect to the ambient plasma. This positive potential is maintained by the motion-induced Electromotive Force (EMF) or by the power supply, depending on the application of the ED tether. Some part of the positively biased tether is uninsulated and exposed to the ambient plasma, collecting ionospheric electrons. Collected electrons are driven as a current inside the tether and emitted from the other end. The current interacts with the geomagnetic field and produces Lorentz force (forward or backward). Drag force is obtained by deploying the tether upwards and collecting electrons through the part near the top end. Thrust is instead obtained by deploying downwards, applying a power supply to reverse the current and collecting electrons at the bottom end. An ED tether travels in LEO under mesothermal conditions, meaning that the electron thermal velocity is much faster than the tether's orbital speed whereas the ion thermal velocity is much slower. In the frame of reference moving with the tether, ions approach the tether at hypersonic speed, get deflected by the very large positive potential on the tether and create a wake behind it. Due to the asymmetry of the plasma distribution, the conventional probe theory becomes almost inapplicable. The asymmetric and non-stable plasma conditions entail the necessity of computational work for the prediction of current collection. A numerical code using a Particle-In-Cell (PIC) method is developed to calculate the electron current collection to a positively charged electrodynamic bare tether.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Onishi, Tatsuo

Advisor dc:contributor.advisor

• Manuel Martínez-Sánchez.

• Aeronautics and Astronautics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/29748

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/29748