The Kuonotori-6, the latest H2 Transfer Vehicle (HTV) to fly from Japan to the ISS, also carried a space debris experiment. After completing its cargo delivering mission (including delivery of the first set of new batteries for the station’s main power system) and loading up with trash and an old set of batteries, it departed the ISS on January 27. Not ones to waste a good opportunity, JAXA had equipped it to carry out additional experiments between undocking and its ultimate fiery demise. For this mission, it carried an electrodynamic tether which, when fully unspooled, would stretch half a mile into space, to test the effectiveness of such a system in passively lowering a satellite’s orbit purely through interaction with the Earth’s ionosphere.
Unfortunately, they ran into problems during deployment. First, one of the four bolts holding the tether’s counterweight failed to separate on the first try. On a second attempt, telemetry indicated that the bolt finally separated, but the tether still would not deploy. Possibly the bolt did not fully separate, or possibly there was some other problem with the mechanism; JAXA engineers will certainly be closely evaluating the telemetry before attempting the experiment again. One thing is certain: they will not be attempting again with this spacecraft: after abandoning the tether deployment, Kuonotori-6 was deorbited last Sunday, making a self-destructive reentry over the South Pacific.
Still, Japanese engineers do not tend to give up easily, so I expect they will try again. They’ll have additional opportunities: although HTV does not fly as often as many other ISS cargo ships, it is vital for delivery of the new batteries for the main power system. New methods for disposal of space hardware is urgently needed; if successful, tethers like this could even be used on things like spent rocket stages, since it is a completely passive system and doesn’t weigh much. Being able to dispose of spent hardware means it doesn’t stick around to contribute to the growing problem of space debris.
So here’s hoping they can get it working next time!