Talk-Polywell.org

Crazy idea: Could a reasonably powered miniature Bussard scoop collect enough particles in earth orbit not to power a fusion rocket, but simply provide a source of fuel for a station-keeping thruster? Most such thrusters try to be extremely efficient of fuel due to obvious problems with resupply, but power is less of a concern. If you could refuel yourself, I'm sure the mass penalties of greater power requirements would be canceled out by the much longer life of the satellite.

As far as I know nobody has solved the problem of a Buzzard ram scoop being very draggy.

One concept I've thought about deploys an array of magnet loops and electrodes to apply a MPD thrust on ambient plasma without bothering to collect it. A Plasma Propeller if you would. Simple, no propellant consumption just electricity, but HUGE for much thrust. The cleanest configuration I've figured would produce a toroidal magnetic field and apply an electric field across the minor radius. As a bonus, a spacecraft in the center could receive some shielding from cosmic rays and solar flairs.

In Earth orbit, all you need is an electro-dynamic tether.

One concept I've thought about deploys an array of magnet loops and electrodes to apply a MPD thrust on ambient plasma without bothering to collect it. A Plasma Propeller if you would. Simple, no propellant consumption just electricity, but HUGE for much thrust. The cleanest configuration I've figured would produce a toroidal magnetic field and apply an electric field across the minor radius. As a bonus, a spacecraft in the center could receive some shielding from cosmic rays and solar flairs.

Sounds kind of like what I was thinking of, but with more appropriate jargon.

Question is, would such a thruster be worth the extra mass of the power generation and the restrictions the thruster design would place on you?

One big question in selecting a thruster system is how much delta_V and impulse it needs to deliver. For limited delta_V, a system that expels propellant is likely to have the edge. The advantage of a plasma propeller or an electrodynamic tether, which does not need to carry propellant, is capacity to provide thrust for an extremely extended period.

As for "In Earth orbit, all you need is an electro-dynamic tether", such tethers are limited in their thrust vector to perpendicular to both the tether and the ambient magnetic field. The tether will fight any static orientation not consistent with the gravity gradient. Depending on the application, that may be enough.

The typical application as I understand it is station keeping mostly for geosynchronous satellites.

What would your huge propellor do to other satellites in geosync?

You have a large magnetic field, but I don't know that that would be a big deal. You're also shooting a stream of ionized particles, generally earthwards to keep in the right orbit, but they tend to do this with the other thrusters used right now anyway, and I can't imagine you needing a lot more mass or charge than they use, so you'd have about the same affect as we have now, aside from the field.

The electromagnetic field produced by a plasma propeller is mostly in or near the conductor array, and probably not all that intense, so no problem unless satellites get too close. In the configuration I described, the most intense fields would be near the center, next most intense near the wires. The stream of ions produced would be of very low intensity, limited by the ambient plasma density, probably not even noticeable without precision instruments.

kunkmiester wrote:You have a large magnetic field, but I don't know that that would be a big deal. You're also shooting a stream of ionized particles, generally earthwards to keep in the right orbit, ...

Earthward??? Wouldn't that be either forward or aft ward depending on the drift?

Don't know if I got something screwed up, but I'd imagine the drift would generally be downwards, towards earth. Towards or away from earth is the more important direction though, because you're mostly worried about screwing with transmissions.

Remember:
Forward outward backward down.
if you thrust yourself forward, you go outward. If you thrust yourself backward you go down.

Of course, with station keeping they MAY use a different saying!

KitemanSA wrote:Remember:
Forward outward backward down.
if you thrust yourself forward, you go outward. If you thrust yourself backward you go down.

Of course, with station keeping they MAY use a different saying!

I liked Niven's version from The Smoke Ring, mainly since I can remember it: East is In, In is West, West is Out, Out is East. Same basic concept though since it helps me remember what happens based on the applied thrust direction.

KitemanSA wrote:Remember:
Forward outward backward down.
if you thrust yourself forward, you go outward. If you thrust yourself backward you go down.

Of course, with station keeping they MAY use a different saying!

your right,
the faster you go the larger your orbit, if you just thrust upwards you ellipse your orbit if I remember correctly. darn, now I am going to have to read something again.

paperburn1 wrote:

KitemanSA wrote:Remember:
Forward outward backward down.
if you thrust yourself forward, you go outward. If you thrust yourself backward you go down.

Of course, with station keeping they MAY use a different saying!

your right,
the faster you go the larger your orbit, if you just thrust upwards you ellipse your orbit if I remember correctly. darn, now I am going to have to read something again.

You make the orbit more elliptical either way, the difference is the axis in which the change happens.