In 1996, Columbia reeled out a satellite on a 19.7-km conducting tether; the line snapped after nearly 5 hours of data, but the system reached about 3,700 volts

On February 25, three days after Space Shuttle Columbia launched on the STS-75 mission, astronauts began deploying a satellite attached to the orbiter by an extraordinarily long conducting tether. The experiment, carried out roughly 160 nautical miles above Earth, looked almost like an absurdly ambitious physics demonstration: Columbia would unreel miles of cable into space and let the system move through Earth's magnetic field. In their joint investigation, NASA and the Italian Space Agency established that the tether burned up and broke after the extension of 19.7 kilometers (approximately 12.2 miles) of cable had spooled out from the cargo bay of Columbia.

A kite string made of physics

This experiment was called TSS-1R, reflight of the Tethered Satellite System, a joint project of NASA and the Italian space agency. The concept itself was so brilliant that it is difficult not to appreciate its simplicity: all one needs to do is drag a conductive wire through the Earth's magnetic field at sufficient velocity in order to create electricity. The resulting electrical circuit interacted with the surrounding ionosphere rather than drawing energy directly from the atmosphere.

The idea came close to realization on February 25th, 1996, when for a brief period of time, the experiment actually worked beyond anyone's wildest expectations. During this stipulated time of successful operation, the system generated significantly more voltage than the engineers had modeled. According to a 1998 peer-reviewed research paper titled “Enhanced electrodynamic tether currents due to electron emission from a neutral gas discharge: Results from the TSS-1R Mission,” published in the journal Geophysical Research Letters, during that time the tether produced an electromotive force of around 3,482 volts and carried nearly 1 amp of current until things went south. NASA, however, estimated the maximum emf to be roughly 3,700 volts in its own summary of the mission, which is about three times greater than the initial estimate by scientists.

Then the wire just let go

According to NASA and ASI, a small flaw in the insulation of the tether allowed an electrical arc to build up against the spacecraft itself, which wore down the Kevlar core of the cable until it was no longer able to bear the strain. The tether tore off, and 19.7 kilometers of cable along with a working satellite were lost to space forever. The satellite separated from Columbia and moved away into its own orbit, while the crew remained in no immediate danger. NASA considered going after the lost payload but quickly realized that chasing after a 12-mile-long wire in orbit around a manned spacecraft wasn't worth the risk.

The real surprise here is just how much science made it out of the mission alive. A separate 1998 paper titled “TSS-1R vertical electric fields: Long baseline measurements using an electrodynamic tether as a double probe,” published in Geophysical Research Letters, notes that the scientists studying the deployment of the cable collected almost five hours of data on ionospheric electric fields before the tether snapped, data that continues to be cited in academic research about tethers to date. The tethered satellite mission, for all its spectacular failure, is remembered as one of the most scientifically productive shuttle missions of the decade.

Why a 30-year-old snapped wire still matters

The real engineering story behind the project is much more exciting than any of that, and serves as an excellent example of how any space agency, despite having billions of dollars at its disposal and years of experience, can be brought down to its knees by a microscopic imperfection in the construction process. And then there's the matter of the technology itself: electrodynamic tethers haven't been forgotten and abandoned after the dramatic failure of the TSS-1R experiment, because they are still considered by many as a possible solution for generating energy without any consumable fuel sources. And it's actually a really useful technology now, when low Earth orbit becomes increasingly crowded with commercial satellites and their waste.