Magnetic self-field effects on current collection by an ionospheric bare tether (original) (raw)
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Performance of Bare-Tether Systems Under Varying Magnetic and Plasma Conditions
Journal of Spacecraft and Rockets, 2000
Electrodynamic tethered systems, in which an exposed portion of the conducting tether itself collects electrons from the ionosphere, promise to attain currents of 10 A or more in low Earth orbit. For the rst time, another desirable feature of such bare-tether systems is reported and analyzed in detail: Collection by a bare tether is relatively insensitive to variations in electron density that are regularly encountered on each revolution of an orbit. This self-adjusting property of bare-tether systems occurs because the electron-collecting area on the tether is not xed, but extends along its positively biased portion, and because the current varies as collecting length to a power greater than unity. How this adjustment to density variations follows from the basic collection law of thin cylinders is shown. The effect of variations in the motionally induced tether voltage is also analyzed. Both power and thruster modes are considered. The performance of bare-tether systems to tethered systems is compared using passive spherical collectors of xed area, taking into consideration recent experimental results. Calculations taking into account motional voltage and plasma density around a realistic orbit for bare-tether systems suitable for space station applications are also presented.
Current Collection to Electrodynamic Tether Systems in Space
2nd International Energy Conversion Engineering Conference, 2004
Three important electrodynamic-tether system configurations have been investigated: an insulated tether with an end body collector, bare tether, and bare tether with end body collector. This paper discusses the current collection capabilities of these configurations and their respective advantages and disadvantages. University of Michigan's TEMPEST computer model was used to conduct the analyses of the three configurations. Analysis has determined that all three configurations allow orbit raising from 400 km to 700 km in around 18.5 days under similar ionospheric and system conditions. In addition, the best tether geometry to use for any of these configurations would be a slotted tether oriented perpendicular to the plasma flow with the individual wires as far apart as possible and as narrow as possible. This would minimize atmospheric drag, increase collision survivability, and keep the electron collection level close to the orbital-motion limit, while increasing the redundancy of the tether in case of micrometer collision..
A Review of Electrodynamic Tethers for Space Applications
44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2008
Space applications of electrodynamic tethers, and basic issues and constraints on their operation are reviewed. The status of the bare-tether solution to the problem of effective electron collection from a rarefied magnetized plasma is revisited. Basic modes of tether operation are analyzed; design parameters and parametric domains where a bare electrodynamic tether is most efficient in deorbiting, rebooking, or power generation, are determined. Use of bare tethers for Radiation Belt Remediation and generation of electron beams for ionospheric research is considered. Teiher heating, arcing, and bowing or breaking, as well deployment strategies are discussed.
Journal of Geophysical Research: Space Physics, 2014
The interaction between a positively biased body traveling through an ionospheric space plasma has direct application to electrodynamic tether (EDT) systems. A 2-D3v particle-in-cell model has been developed to study the plasma dynamics near a positively charged EDT system end-body and their impact on the current collected. The results show that the azimuthal current structures observed during the reflight of the tethered satellite system (TSS-1R) mission develop in the simulations and are found to enhance the current collected by the satellite by 67% when the magnetic field is ∼ 15 • off of perpendicular to the orbital velocity. As the component of the magnetic field in the simulation's plane increases, the electrons are not able to easily cross the field lines causing plasma lobes to form in the +y and −y regions around the satellite. The lobes limit the current arriving at the satellite and also cause an enhanced wake to develop. A high satellite bias causes a stable bow shock structure to form in the ram region of the satellite, which limits the number of electrons entering the sheath region and thus limits the current collected. Electron-neutral collisions are found to destabilize the bow shock structure, and its current limiting effects were negated. Analytical curve fits based on the simulations are presented in order to characterize the dependence of the current collected on the magnetic field's orientation, space plasma magnetization, and satellite potential. The variations in the collected current induced by space plasma environmental changes may introduce new instabilities in an EDT system's dynamics.
Effect of magnetic field on current colection on bare tether in LEO
Aiaa Asme Sae Asee 38th Joint Propulsion Conference and Exhibit Proceedings of the Conference 38th Aiaa Asme Sae Asee Joint Propulsion Conference Exhibit 7 10 Jul 2002 Indianapolis Indiana, 2002
An eiectrodynamic Tether is a long thin conductive string deployed from a spacecraft. A part of the ED tether near one end, which is rendered positive by the Electromotive force (EMF) along the tether, collects electrons from the ambient plasma. In the frame of reference moving with the tether, ions flow toward the tether, get deflected near the tether by its high positive potential and create a wake. Due to the asymmetry of plasma distribution and the weak but significant Geomagnetic field, the conventional probe theory becomes almost inapplicable. Computational work for the prediction of current collection is thus necessiated.. In this paper, we analyze effects of magnetic field on velocity distribution fantion at a point that is far from the tether, and discuss a new way to treat electrons at computational boundary. Three cases with different magnetic field are simulated and compiled so as to provide a part of the pre-ftight prediction of the space experiment by NASA ProSEDS, which is planned September 2002. Plasma oscillations and associated increased electron density due to trapped electrons are recognized in the computation when the magnetic field is absent. In the presence of magnetic field, current collections tend to be £~ 3 higher than the 2D Orbital-Motion-Limit (OML) without significant appearance of trapped electrons. It is argued that, because of the three-dimensional motions of electrons, the 3D OML limit may be the upper limit even though the geometry is two-dimensional.
Science with an electrodynamic tether
Proceedings of the International Round Table on Tethers in Space International Round Table on Tethers in Sp 28 30 Sep Noordwijk, 1994
Ionospheric interaction experiments using a conductive, fully bare tether are discussed. With an optimal design, requiring 1.15 mm diameter and 7.5 km full length for a collected current of 0.87 A at day conditions, the tether radiates 0.33 watts as Fast Magnetosonic waves and 0.16 watts as Alfven waves. Secondary keV electrons are produced over a 6.5 km length, giving raise to noticeable auroral effects in the D-layer, at low geomagnetic latitudes. A preliminary design of the experiment, to be implemented on either a satellite or a Station, has been carried out. An ejector gives an initial velocity to an end mass, a free spool of tether unwinding from that mass during a first stage of deployment; other phases are monitored through the tether velocity, driving a reel with an unwinding device.
A review of electrodynamic tethers for science applications
Plasma Sources Science and Technology, 2010
A bare electrodynamic tether (EDT) is a conductive thin wire or tape tens of kilometres long, which is kept taut in space by gravity gradient or spinning, and is left bare of insulation to collect (and carry) current as a cylindrical Langmuir probe in an ambient magnetized plasma. An EDT is a probe in mesothermal flow at highly positive (or negative) bias, with a large or extremely large 2D sheath, which may show effects from the magnetic self-field of its current and have electrons adiabatically trapped in its ram front. Beyond technical applications ranging from propellantless propulsion to power generation in orbit, EDTs allow broad scientific uses such as generating electron beams and artificial auroras, exciting Alfven waves and whistlers, modifying the radiation belts and exploring interplanetary space and the Jovian magnetosphere. Asymptotic analysis, numerical simulations, ground and space tests and past and planned missions on EDTs are briefly reviewed.
CURRENf COU.ECTION AND CURRENT CLOSURE IN THE TETHERED SATELLITE SYSTEM
2020
In this paper we address two aspects of the Tethered Satellite System: i) the current collection in the vicinity of the tethered satellite and il) the appropriate physics for modeling the closure path of the tether current in the ionosphere. Our approach to the issue of current collection has been based on numerical simulations performed with one and two dimensional codes. We have found that during transient current collection a positively charged body will attract an electron current which is greater than the steady state value by a factor > 40. The mechanism responsible for this is the influence of plasma ions while they are being evacuated from the sheath region. The duration of the enhancement for ionospheric conditions at 300km altitudes is on the order of a millisecond. During this transient phase some of the electrons in the sheath are accelerated to energies of twice the applied potential. The structure of the evolved sheaths in the simulations indicates that electron col...