>>6511947Interesting. Cheers, anon.
STS-75 mission scientists hoped to deploy the tether to a distance of 20.7 kilometers (12.9mi). Over 19 kilometers of the tether were deployed before the tether broke. It remained in orbit for a number of weeks and was easily visible from the ground, appearing something like a small but surprisingly bright fluorescent light traveling through the sky.

TSS-1R tether composition [NASA].
The electric conductor of the tether was a copper braid wound around a nylon (Nomex) string. It was encased inteflon-like insulation, with an outer cover ofkevlar, inside a nylon (Nomex) sheath. The culprit turned out to be the innermost core, made of a porous material which, during its manufacture, trapped many bubbles of air, at atmospheric pressure.
Later vacuum-chamber experiments suggested that the unwinding of the reel uncovered pinholes in the insulation. That in itself would not have caused a major problem, because the ionosphere around the tether, under normal circumstance, was too rarefied to divert much of the current. However, the air trapped in the insulation changed that. As it bubbled out of the pinholes, the high voltage of the nearby tether, about 3500 volts, converted it into a plasma (in a way similar to the ignition of a fluorescent tube), a relatively dense one and therefore a much better conductor of electricity. This plasma diverted to the metal of the shuttle and from there to the ionospheric return circuit. That current was enough to melt the cable.
The specific TSS1-R mission objectives were: characterize the current-voltage response of the TSS-orbiter system, characterize the satellite's high-voltage sheath structure and current collection process, demonstrate electric power generation, verify tether control laws and basic tether dynamics, demonstrate the effect of neutral gas on the plasma sheath and current collection, characterize the TSS radio frequency and plasma wave emissions and characterize
