Japanese ISS Supply Ship Dual-Purposed As Tether Experiment

When a rocket sends a capsule up with supplies for the International Space Station, they usually send a bunch of their trash back down with it, all of which burns up in the atmosphere on re-entry. But as long as you’ve got that (doomed) vehicle up there, you might as well do some science with it along the way. And that’s exactly what the Japanese Space Agency (JAXA) is doing with their Kounotori 6 supply ship that just left the ISS on Friday.

The experiment is with an electromagnetic tether that can be used to either turn electrical energy into kinetic or vice-versa. When you string a long conducting wire outwards from earth, the two ends pass through the earth’s magnetic field at different altitudes and thus pass through magnetic fields with different strengths, and an electrical potential is generated. In the KITE experiment (translated), a resistive load and an electron emitter on the supply ship are designed to burn up this electrical energy, lowering the ship’s kinetic energy, and dropping its orbit down to earth.

The eventual plan is to use a tether system like this to remove kinetic energy from space junk, pulling it out of orbit and out of harm’s way without requiring the ship to carry extra fuel to do so. The seven-day test mission will investigate thrust and current generated by the 700-meter-long aluminum wire, as well as experimenting with controlling it as it unfurls. The video, embedded below, makes it look like they’re going to actively control the load to stabilize the end of the tether relative to the ship. Anyone want to chime in on that? This isn’t the first time an electrodynamic tether has been tested in space, but with some luck, it will be the first successful test in orbit.

This is definitely not a hack, and the science is really cool. But cleaning up the space junk with a freighter that’s bound to burn up in the atmosphere is a win. The ISS gets rid of its metaphorical dirty laundry, which is mostly expended batteries, and the orbit gets cleaned up to boot. We wish them the best of luck.

Via [Spaceflight Now].

35 thoughts on “Japanese ISS Supply Ship Dual-Purposed As Tether Experiment

    1. it might be a matter of scale, both of power generation and general geometry, the volume and mass of power generation required to get a useful effect in propulsion mode, now this is pure guesswork though.

      what i have in my mind is an issue where a satellite needs more and more cable and more and more solar cells which in turn requires more thrust that in turn requires more cable.

      there might easily be scales where it works well and a sufficiently effective method of power generation that might make it possible and this is of course all only when converting electrical to kinetic energy, not when converting kinetic energy to electrical.

    2. Because all the tests failed.

      It’s also not a power source, as this effectively turns orbital velocity into electricity. Drawing more power reduces velocity, lowering your orbit. Do that enough and bad things happen.

      Here’s the cool part: this works both ways, so putting power into the tether increases your orbital velocity. Yes, it’s like the EM drive, where it turns electricity into thrust, but this is real. You can only do it in a magnetosphere, but it’s real.

      But again, the tests failed. The shuttle experiments had trouble deploying the tether, and manufacturing defects with the tether. There is a Japanese cubesat tether experiment in development, but I haven’t heard anything about that in years. It’s just a very, very hard problem to solve.

      1. isnt lowering ones orbit without propellant a good thing in many cases?

        i sort of thought that was the entire point.

        as far as i know it is proven to work, even though there were issues deploying the tether on the original TSS-1 there was a reflight of the entire experiment that did get useful data.

      2. Correct but you could use orbital velocity as a storage system. When you are in sunlight you use the tether to boost your orbit and when it is dark you use it to lower your orbit.
        Using it for de-orbit is kind of useful but using it to keep thinks in orbit seems like a big win for me. I guess if it you make it light enough you could use it to de-orbit upper stages.

      3. “as this effectively turns orbital velocity into electricity. Drawing more power reduces velocity

        Right.. if you don’t have a good answer then let someone else have a shot I would say.

    1. Probably not any more hazardous than the crap that’s coming into the atmosphere from small meteors and dust already. We get around 60 tons of space dust bunnies every day.

    1. It’s a big planet, and Barry mentioned we get 60 tons of naturally-occuring space garbage falling on us every day. If you’re worried about pollution there’s a million other things that are easier to fix and would make a bigger difference.

  1. If the tether is strung away from the Earth a tension will exist and the further, the greater the tension. It should lay itself out straight away with a little time. The tension is from the ends of the tether orbiting at two different altitudes and having two different orbital periods – if they were not connected that is. Check the web site for Tethers Unlimited, created by Robert Forward.

    I don’t see how this does anything without being a loop.

  2. I understand what can create a potential between two points but not how the return circuit works. Throw out more wire for a ground plane? Run a return leg, it also has the same potential.

    The first shuttle experiment had quite a high voltage light show from what I heard about and what I saw a little of on NASA Select.

    1. That’s the “electron emitter” part mentioned above (@The Regnirps): right, a loop wouldn’t work, because it would “feel” the same potential difference. So you have to “throw out” the excess electrons at the negative side. Let ’em take care of themselves :-)

      1. But then where do the electrons come from in a steady state of operation? I see one side becoming ever more positive and attracting the electrons back, so total momentum stays constant…

        1. Hm. There’ll be some plasma around. You’re right that they’ll need some kind of “electron receptor” at the other side. otherwise the whole contraption will become so positive that it’ll be difficult to “emit electrons” in the first place :)

          Whether the momentum involved in trading electrons with the environment can be put into some meaningful relation with the momentum change from the Lorentz forces acting on the wire is left as an exercise for the reader…

          1. I actually believe a loop could work, as magnetic dipoles (one earth, other satellite’s loop) can attract and repel each other (i.e. not only apply torque but a translational linear force as well)

  3. I’m ignorant of the facts but after spending enormous bucks getting those valuable minerals up there shouldn’t we just pile them up somewhere where we can use them later? I suspect that they would be worth a significant amount in about 20 or so years. I’d gladly invest in a couple of tons of lithium in orbit.

    1. Not practical except maybe geostationary, and those have ‘graveyard’ orbits.

      Each object is going around 7 kilometers per second, and for non equatorial orbit they tend to not be going the same direction exactly. Getting all the stuff gathered up onto one spot is very hard, probably harder than launching new stuff. Also, the worst debris is in low Earth orbit and their orbit will decay due to ‘air’ resistance eventually.

      Check out http://www.stuffin.space for a good visual.

  4. @Brian Benchoff,

    Thanks for posting this and aggregating links for us. I planned to delve into this today to learn more. You just made my task a lot easier! This is one reason I come to HaD regularly. Thanks again, David

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