5 research outputs found
A new kind of dynamic instability in electrodynamic tethers
No full textAbstract. Simulation of the dynamics of an electrodynamic tether on a circular inclined orbit shows a
very complex motion driven by the electrodynamic forces acting on the conductive tether. These
forces depend on the current owing in the wire, the Earth magnetic eld, the orbital velocity
and the tether position. In this paper we use a simple model to describe the dynamic eects of
these forces. The tether is modelled as a rigid rod with point masses at the ends. We also adopt
a non-tilted dipole model for the Earth magnetic eld, and we assume that the tether current is
constant. When the current is null, the sytem has a stable equilibrium position with the tether
aligned along the local vertical. When the current is dierent from zero, a periodic motion appears.
A non-linear analysis of the motion shows that the periodic solutions are always unstable (within
the limitation of the model considered in the paper). The physical reason for the instability is
that the electrodynamic forces pump energy continually into the system. The net energy increase
per orbit for the periodic solution (or state space trajectory) is zero. However, any non-periodic
trajectory in its neighborhood has a positive net energy ux per orbit so that after several orbits
the in plane libration becomes a rotation. The mechanism responsible for this instability depends
on the orbital inclination. Unlike other destabilizing mechanisms found in electrodynamic tethers,
this one is present in any kind of tether system with either a exible or a rigid tether, operating
in the generator or thruster mode and utilizing a bare tether or a large spherical termination to
collect the ionospheric electrons. The instability described in this paper is independent of the
presence of resonant force components that may be generated by the magnetic and plasma elds
Three-Body Dynamics and Self-Powering of an Electrodynamic Tether in a Plasmasphere
No full textThe dynamics of an electrodynamic tether in a three-body gravitational environment are investigated. In the classical two-body scenario the extraction of power is at the expense of orbital kinetic energy. As a result of power extraction, an electrodynamic tether satellite system loses altitude and deorbits. This concept has been proposed and well investigated in the past, for example for orbital debris mitigation and spent stages reentry. On the other hand, in the three-body scenario an electrodynamic tether can be placed in an equilibrium position fixed with respect to the two primary bodies without deorbiting, and at the same time generate power for onboard use. The appearance of new equilibrium positions in the perturbed three-body problem allow this to happen as the electrical power is extracted at the expenses of the plasma corotating with the primary body. Fundamental differences between the classical twobody dynamics and the new phenomena appearing in the circular restricted three-body problem perturbed by the electrodynamic force of the electrodynamic tether are shown in the paper. An interesting application of an electrodynamic tether placed in the Jupiter plasma torus is then considered, in which the electrodynamic tether generates useful electrical power of about 1 kW with a 20-km-long electrodynamic tether from the environmental plasma without losing orbital energy
