Robust Flight Tether for In-Orbit Demonstrations of Coulomb Drag Propulsion

Abstract

A new method of producing robust multi-wire tethers for Coulomb drag applications was developed. The multi-wire structure required for redundancy against the micrometeoroid flux of the space environment is realised through the method of wire twist bonding traditionally used for chicken wire. In the case of the Coulomb drag tether, the diameter of the individual wires is 50 μm, which introduces the main technological challenge. To manufacture the tether, a manually driven tether machine was designed and built. Two multi-wire tethers for Coulomb drag applications were produced for two in-orbit demonstrations of the FORESAIL-1 and ESTCube-2 CubeSat missions. The flight tethers were both 60 m long as produced, clearly demonstrating beyond the level of proof of concept the applicability of both the method and the manually driven tether machine. Altogether, 6480 twist bonds were produced without a single wire cut. In this paper, the requirements for the tether are listed and justified. The production method is reviewed, and the 4-wire tether produced is evaluated against the requirements. Finally, the test procedures of the tether are described, and on the basis of the results, it is concluded that the tether can tolerate a tension of 14 g without the twist bonds slipping or the tether structure collectively collapsing. Furthermore, the tether can be reeled from the production reel to the flight reel, which simplifies the final integration of the tether reeling system with the Coulomb drag propulsion device.