A Tether Deployment System for Picosatellites

Daniel Bunker
Saber Astronautics Australia, Pty Ltd

Jason Held
Saber Astronautics Australia, Pty Ltd

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     Last modified: July 29, 2011

Abstract
There is growing interesting in the use of electrodynamic tether systems aboard satellites for de-orbit and power generation. We present a portable tether deployment system for use on picosatellites that is suitable for such applications. The system can be produced at low cost and has little impact on the mass and space constraints of conventional picosatellite buses.

The design space considers two mission options—passive and active electron emission. In a passive system induction from the interactive of a conductive tether moving through a magnetic field is used to generate a current. This current then interacts with the magnetic field to provide a Lorentz drag force which leads to fast deorbit times. Active systems result in much higher current generation by placing an electron emitter at the nadir or main bus end of the system. Current can be forced to flow towards the main bus and collected, providing added redundancy to the spacecraft system, or away from the bus providing a drag force. Current loops are closed via interaction of charged particles in the ionosphere.

Orbit Motion Limited theory is used to estimate the current within a tether system and from this the Lorenz force drag induced by both passive and active methods. An active system in low Earth orbit (LEO) can provide power on the order of nearly 200mW, which is significant for picosatellite applications. Alternatively, the system can be used for de-orbit which can be achieved within approximately 2 weeks (from LEO). A prototype of the baseline tether deployment system for such applications was manufactured from aluminium 6061 and weighed approximately 95 grams, taking up less than 10% of the total internal volume of a conventional Cubesat. We present this system as a possibility to incorporate into future picosatellites to provide additional power to the EPS, especially on the dark-side of the orbit where solar panels are unable to provide energy.

Such a system will allow for the safe removal of spent satellites at end of mission life, hence reducing the accumulation of space junk at low orbital altitudes. As such, it provides redundancy and additional power, and is a generic, cost effective, Australian ready solution to lessen the environmental impact of picosatellite missions.