Electron emitters are an essential part for a number of space technologies including managing of spacecraft charging, providing neutralisation for ion thrusters or to drive a current through an electrodynamic tether that interacts with the Earth’s magnetic field. Such a tether may provide a very elegant way to deorbit or reboost spacecraft in the ever growing LEO environment using only the Lorentz force. The currents required are just below the Ampere range, which are traditionally generated with hollow cathodes that consume on-board propellant. Classical propellant-less so-called cold cathodes, based on CNT or silicon tip arrays, only exist for very small currents in the micro- to milli-Ampere range. Scaling them up to the hundred milli-Ampere range leads to very large and heavy surfaces as well as high electric power, which is not available for most applications.
Here, we are proposing a novel new idea: Standard electron emitters are built in such a way that they emit electrons in one direction. For a tether applications (and others like spacecraft charging), this is not necessary. Instead, we are proposing a new design where electrons are emitted radially on top of a boom, which enables a much more compact emitter and a design that is easily scalable to provide the necessary currents. It consists of a single CNT fiber in the center with a radial mesh electrode. The maximum current is then only a function of the length of the emitter/mesh assembly. By mounting the emitter on a boom, the electrons will not hit the spacecraft surfaces. In addition, no surface area is lost, which is crucially needed for solar cells to generate electric power.
This technology building-block can enable a consumeable-less tether system that deorbits satellites at the end of their life using a compact and light autonomous kit. This would be highly synergetic with ongoing efforts for the H2020 funded E.T.Pack project, which develops such a technology using a classical hollow cathode.
