The radiation impedance of orbiting conductors

The dispersion relation for waves in a cold, magnetized plasma is discussed using the potential for the longitudinal part of the electric field. This clarifies wave emission from a conductor in low Earth orbit and should be useful in considering the far field and both hot plasma and nonlinear, near‐field effects. General formulas for radiation impedance are directly obtained. For tethers a fundamental dependence on contactor size is discussed. Spherical and ellipsoidal contactors and an (anodeless) bare tether are considered. Simple arguments on nonlinear contactor effects lead to a surprisingly simple result for impedances off the Alfvén branch.