ESA develops “snap-proof” space tether

This month, the University of Helsinki and the European Space Agency (ESA) will test a new space tether that has less chance of snapping under the stresses of operating in orbit.

Installed aboard Estonia’s ESTCube-1 cubesat, the new tether is scheduled to be launched with ESA’s Proba-V satellite atop a Vega rocket as part of an experiment in developing an electric solar sail.

Tethers have been around since the United States’ Gemini 11 deployed one in 1966 to help control the capsule’s rotation. These tethers are routinely used to despin satellites by playing out weights from a spinning spacecraft. As the weights move further away, the satellite’s rotation slows down. When the spin rate is suitably slow or stopped, the tethers are released in an outer space version of “crack the whip” and the spin energy is carried off by the weights.

However, tethers have much greater potentials than just despinning satellites. They also hold the promise of allowing spacecraft to lower sensor packs from orbit into the Earth’s outer atmosphere, generate electricity by acting as an armature as they moves through the Earth’s magnetic sphere and even providing propulsion in the form of an electric solar sail.

The problem is, space tethers are a formidable engineering challenge. They need to be thin, light and flexible in order to fit inside of a spacecraft or launch vehicle, they need to be extremely long, they need to be strong enough to support a payload as well as their own weight, and, if they must transmit power or data, they need to maintain internal integrity. In other words, it doesn’t help if the tether doesn’t break if the electric wire inside snaps. At the moment, experimental tethers haven’t had a great track record. About half fail to deploy, snap or are broken by micrometeoroids.

Researchers at the University of Helsinki believe that they’ve come a step closer to a solution with a new tether that is about half the diameter of a human hair. The 50-micrometer aluminum tether has a smaller 25-micrometer wire woven into it. The clever bit is that the Helsinki team used ultrasonic welding techniques from the microelectronics industry to cross connect several wires together every centimeter. These “subwires” allow electricity to flow through the wire even if the tether stretches, causing the wires to break. If only one subwire remains intact, the current still flows.

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