electrodynamic motors

[joiz]

you know how they tried to use tethered satelites to generate electricity by turning it into a generator? well a generator can also be made into a motor, couldn't they make electrodynamic RCS or even main engines?

 

[Hielor]

you know how they tried to use tethered satelites to generate electricity by turning it into a generator? well a generator can also be made into a motor, couldn't they make electrodynamic RCS or even main engines?

With nothing to push against in space, you can't turn that energy into linear force.

 

[sputnik]

Quite possible, yes.

I believe this method has been used in conjunction with momentum wheels for satellite RCS -- the magnetic torquers provide a way to dump momentum-saturation of the wheels.

It could be used as main propulsion, but it's not very powerful and requires quite a bit of power and tether length, so you usually see it proposed as a way of maintaining altitude in a big tether system.

 

[Kozak]

With nothing to push against in space, you can't turn that energy into linear force.

Well, so magnetic levitation doesn't exist?..
http://en.wikipedia.org/wiki/Electrodynamic_tether

couldn't they make electrodynamic RCS or even main engines?

Tether propulsion has even less thrust than ion drives. It's main advantage is lack of fuel consumption - a nuclear powered tehered satelite pair can theoretically stay in orbit forever even on LEO.

 

[Hielor]

Well, so magnetic levitation doesn't exist?..
http://en.wikipedia.org/wiki/Electrodynamic_tether

Ah, yeah, that's rather more feasible. I thought by "electrodynamic drive" he was referring to something such as the Dean Drive. Carry on.

 

[Andy44]

I believe this method has been used in conjunction with momentum wheels for satellite RCS -- the magnetic torquers provide a way to dump momentum-saturation of the wheels.

Hubble Space Telescope uses wheels for attitude control actuation and magnetic torquers to dump momentum.

http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-103/12_23_15_38_33.html

This is quite common in LEO. Hubble has no propulsion system at all; it's placed in a high enough orbit that during its lifetime it should never need a boost (between service missions, at least), so it is totally dependant on mag torquers for momentum unloading.

As for propulsion without reaction mass, you can start reading here:

http://en.wikipedia.org/wiki/Tether_propulsion#Electrodynamic_tethers

Electrodynamic tethers
Main article: Electrodynamic tether

Electrons flow through the conductive structure of the tether to the power system interface, where it supplies power to an associated load, not shown. (source: U.S. Patent 6,116,544, "Electrodynamic Tether And Method of Use".)


In a strong planetary magnetic field such as around the Earth or Saturn, a conducting rotovator can be configured as an electrodynamic tether. This can either be used as a dynamo, which slows the tether and changes the angular momentum whilst generating electrical power, or alternatively, its orbital speed and/or angular momentum can be increased electrically from solar or nuclear power by running current through a wire that goes the length of the tether. Thus the tether can be used either to accelerate or brake an orbiting spacecraft.
In both cases the tether pushes against the planet, and thus the momentum gained or lost ultimately comes from the planet.
One complication to these techniques is that if the tether rotates, the direction of current must reverse (such as is the case in alternating currents).

 

[sputnik]

Ayup. I'd be tempted to build an add-on (I HAVE been tempted to build an add-on), but I don't have a good model of magnetic flux. (Let alone one that would work for other planets). Plus, actually operating the thing would be as boring as watching paint dry. What I really would want to do is create an energy-maintenance system for automatic operation on a rotorvator of some kind.

 

[tblaxland]

you know how they tried to use tethered satelites to generate electricity by turning it into a generator? well a generator can also be made into a motor, couldn't they make electrodynamic RCS or even main engines?

Yes, that is the principle of operation behind the Ananke Tether-Sling project that n0mad23 & I were working on. That design in turn was based on the NASA MXER (Momentum Exchange Electrodynamic Reboost) tether as well as similar designs by Tethers Unlimited (there is some info on their site here).

You can get an early version [ame="http://www.orbithangar.com/searchid.php?ID=3399"]here[/ame]. The electrodynamic reboost was never implemented (it is a one shot only, proof of concept) but it was intended to be solar powered and we did some calculations to get the solar panel area roughly right, including power for the electromagnetic payload catcher and 8 week reboost interval. The dev thread here has lots more info if you can stand to wade through all 10 pages...

---------- Post added at 08:11 ---------- Previous post was at 07:53 ----------

Ayup. I'd be tempted to build an add-on (I HAVE been tempted to build an add-on), but I don't have a good model of magnetic flux. (Let alone one that would work for other planets).

Some data from Magsat here:
http://en.wikipedia.org/wiki/Magsat

 

[simonpro]

The three most useful papers relating to MAGSAT are:
http://www.agu.org/pubs/crossref/1985/JB090iB03p02495.shtml
http://www.agu.org/pubs/crossref/1982/GL009i004p00243.shtml
http://www.agu.org/pubs/crossref/1980/GL007i010p00793.shtml