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Cheap Astronomy
2018-Jan-23, 09:51 AM
I was reading this UT article: https://www.universetoday.com/138314/new-kind-propulsion-system-doesnt-need-propellant-it-converts-electricity-into-thrust-and-vice-versa/. Maybe the answer is in UT's comments area, but I find them hard to access and hence I couldn't pose my question there either.

Anyway, I could not glean from the article how this tether system generates thrust. I sort of get how it generates electricity, but how do you get from there to propellant-free thrust? Is it some kind of photon propulsion and if that's it could it really generate enough thrust to prevent orbital decay?

Thanks

DaCaptain
2018-Jan-23, 02:54 PM
I was reading this UT article: https://www.universetoday.com/138314/new-kind-propulsion-system-doesnt-need-propellant-it-converts-electricity-into-thrust-and-vice-versa/. Maybe the answer is in UT's comments area, but I find them hard to access and hence I couldn't pose my question there either.

Anyway, I could not glean from the article how this tether system generates thrust. I sort of get how it generates electricity, but how do you get from there to propellant-free thrust? Is it some kind of photon propulsion and if that's it could it really generate enough thrust to prevent orbital decay?

Thanks

It seems to me that the tether generates an electric current that can then be used for propulsion. A replacement for solar collectors? But the though of having kilometers long tenders danging from off a satellite seems like a big no-no to me. It could be easily cut or entangled with another satellites tether. Once cut loose the tether would prove to be quite the obstacle to other satellites and spacecraft.

antoniseb
2018-Jan-23, 05:22 PM
It seems to me that the tether generates an electric current that can then be used for propulsion. A replacement for solar collectors? But the though of having kilometers long tenders danging from off a satellite seems like a big no-no to me. It could be easily cut or entangled with another satellites tether. Once cut loose the tether would prove to be quite the obstacle to other satellites and spacecraft.
The tether they already tried generated electricity by dragging through the magnetic field and slowing its orbit. I suppose it would be possible to reverse the current and use it to thrust against the magnetic field to raise the orbit.

Jeff Root
2018-Jan-23, 06:10 PM
How the thing works is finally explained a little bit if you scroll far
down past a mass of advertisements. It still isn't clear. There is
a link in that section that is supposed to be to a more detailed
explanation. I haven't followed it yet. Although they try to make
it sound like something new, my impression is that antoniseb's
guess is probably correct. A conducting tether moving through
Earth's magnetic field can transfer energy to or from the field,
speeding up or slowing down whatever it is attached to, like a
very simple electric motor.

-- Jeff, in Minneapolis

Jeff Root
2018-Jan-23, 06:30 PM
The link just goes to the Wikipedia article on 'Lorentz force'.
The Universe Today article is pretty strongly dumbed-down,
while the Wikipedia article is heavily mathematical. Nothing
comfortably in-between. I can't tell whether this particular
tether is supposed to work on static electric charges or
induce a current in the tether. I would expect the latter, but
the language used suggests the former.

-- Jeff, in Minneapolis

Solfe
2018-Jan-23, 09:57 PM
I know JAXA was working on a tether craft that generated electricity from the earth's magnetic field. Instead of using electric engine, they used the energy to blow off carbon to get thrust. I believe it is in the planning stages. The beauty of the system was you didn't have an expensive engine, only benign carbon. It certainly wasn't planned to be very powerful. It probably has orbital characteristics that doesn't require much need for thrust.

This seems different.

Grey
2018-Jan-24, 06:48 PM
I'm pretty sure that antoniseb has the right of it: you're dragging a conductive wire through the Earth's magnetic field, so that can either by used as a dynamo, to generate electricity from the kinetic energy lost, or in reverse, as a motor.

Here (http://www.davidbrin.com/tankfarm.htm)'s an entertaining short story that features the concept as the real protagonist of the story. ;)

slang
2018-Jan-24, 11:45 PM
If you look up the guy they interviewed for the article on Google Scholar, you'll find lots of papers on space tethers that he participated on. Maybe they patented a particularly efficient material for tethers?