Multi-Wire μ-Tether for Plasma Brake and Space Debris Mitigation

Plasma Brake is a compact module to be mounted to a spacecraft or to a piece of space junk for orbital braking and ultimate atmospheric demise. The braking force is generated by the ionospheric plasma Coulomb drag that is analogous to the air drag in the neutral atmosphere. The dragging obstacle against the orbital plasma RAM flow is established by an electrostatic field with a high voltage difference with respect to the ambient plasma, typically -1 kV. The potential structure is supported by a long 4-wire tether with single aluminium wires with thickness of less than 50 μm. The redundant structure makes the tether resilient against μ-meteoroids. However, the hair-thin tether sets no harm to other space assets based on micro-meteoroid and space debris flux models such as MASTER-2009.

 

The multi-wire structure required for redundancy against the µ-meteoroid and space debris flux of the space environment is realised through a method of twist bonding traditionally used for the chicken wire. In the case of the Coulomb drag tether, the diameter of the individual wires is at most 50 µm, which introduces the main technological challenge. Preceding this method, ultrasonic bonding and cold welding were used for tether production until the twist bonding method was developed and adopted. 

 

Until recently, the tethers have been produced running a manually operated machine while an automated tether factory has been developed alongside with manual production. Presently, we have manually produced three flight tethers each 60 metres long for three CubeSat missions of FORESAIL-1, EstCube-2, and FORESAIL-1p. One of the objectives of our CubeSat missions is to test the Plasma Brake tether deployment and high-voltage power systems, and most significantly measure the Coulomb drag effect in orbit. The first version of the automated factory was successfully run late 2024. Several samples with a length of 100+ metres were successfully produced. The second version of the tether factory is ready for set up and test runs in May,  2025. The aim is to produce tether samples with a length of 1000+ metres. This work is a central part of the Dragliner project of ESA aiming at a fully functional Plasma Brake engineering model at TRL of 5-6.