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Spacecraft May Surf Magnetic Fields
Maggie McKee writes "Future spacecraft may surf the magnetic fields of Earth and other planets, taking previously unfeasible routes around the solar system, according to a proposal funded by NASA's Institute for Advanced Concepts. The electrically charged craft would not need rockets or propellant of any kind. To get charged up, the spacecraft could either fire a beam of charged particles into space or simply allow a radioactive isotope to emit charged particles. Because long, thin filaments have large surface areas for holding charge, the spacecraft might look like Einstein's head — with wiry filaments sticking out at all angles — or a weird space 'stocking.'"
It's not stupid. It's Advanced.
The Sun's magnetospere is bigger than the orbit of Pluto if I remember correctly. And it doesn't have to be exclusive, you could use the magnetic "sock" for a stage of the journey and maybe propellents in another stage of the same voyage and then you short range teleport for the last 5000km ;). It's just another useful tool to employ from a mission planning perspective.
Shh.
Where did those people study Physics? It doesn't work that way.
The only surface area that matters is an equipotential surface, so in the case of "filaments sticking in all directions" it will be a roughly spherical surface formed by the ends of filaments. Within this sphere there is almost no electric field -- filaments can be seen as a kind of lightning rods, except there is no lightning because they are in vacuum. So at best they will have a larger sphere, at worst a cigar or other shape with less surface area. If one has to build a large but light sphere, he can make it out of the wire mesh -- in vacuum it won't discharge like it would in the air, where those spheres have to be smooth. Filaments or spikes can be useful for acceleration of charged particles.
As for usefulness of the whole thing, I guess, you can use this for steering the spaceship, however the analogy to surfing is very poor. Surfboards can accelerate by absorbing the energy of waves moving from deep to shallow water. This thing flies through a stable magnetic field, steering by changing its electric charge. A better analogy would be a sailboat changing tacks, with gravity acting as a wind and magnetic field as water resistance.
Contrary to the popular belief, there indeed is no God.
Mason Peck of Cornell University in Ithaca, New York, US, has received a grant to study the idea, which is based on the fact that magnetic fields exert forces on electrically charged objects with a velocity that is not parallel with the field lines.
I'm guessing this system will work by having an orbit that travels over the magnetic poles, as the magnetic field lines are much closer there, and reversing the charge between poles so that it doesn't end up at the same altitude as it started. One problem, the further you get from Earth, the further apart the lines and therefore, less force. It seems as if it's going to take a very long time to get anything close to an escape velocity (if even possible). Who knows, it may even be more efficient to just shoot those charges out the back, aka ion drives.
Anyone who remember physics 101 will recall the following:
A magnetic field will create a force normal to the velocity of a charged object. So
1. The force on any charge will be normal to the velocity, so it will move around in circles. This includes the charged spacecraft. (The field here is not homogeneous, but still, no gain in energy)
2. A current loop(i.e. a moving charge) can change the energy or be accelerated in a magnetic field.
(2) is and has been used since the first satellites were orbited to do orbital corrections, and are well understood and used. It can allow the life of the satellite to be expanded by many years.
Why would this craft not just use a long current carrying wire instead.
don't cut it off www.mgmbill.org
Corona in a gas is easy to produce because gas can be ionized by strong electric field along the spike or fiber, giving you a lot of charged particles to carry your discharge current. In vacuum you have nothing but those electrons that are already in metal -- you can emit them if you are negatively charged, and can't emit anything if you are positively charged (think of it as a giant diode tube). Even if you emit electrons, you have to move very fast so magnetic field will divert them away from you, and once you are sufficiently positively charged, emission will stop.
Most likely at best this will produce a cloud of electrons following a positively charged spaceship, so forces that magnetic field applies to both will almost completely compensate each other. With radioactive source of charged particles (positively or negatively charged), or electron cannon you can produce more charge on the spacecraft, and probably it can be combined with ion engine that produces charged particles anyway.
Contrary to the popular belief, there indeed is no God.
Why do I feel the need to point this out?
I know what he meant, but why did you make me reply? Damn you, EE degree, stop controlling my life!
It will be the same as in vacuum tubes and CRTs -- spikes themselves won't do much, but you can heat up the cathode, and create some electric field with anode -- electrons will be emitted, some of them will be captured by anode, the rest will escape the device, leaving it positively charged. As long as anode is positive relative to cathode, electron cannon will work. You can lose electrons until the point when you are so positively charged that all electrons that left the cannon have less energy that it is necessary to leave the spaceship.
Or you can make a source of positively or negatively charged ions -- they can be accelerated in a similar way. Again, this probably can be much easier achieved by messing with an ion engine, under/over compensating the positively charged ions that leave the engine.
Contrary to the popular belief, there indeed is no God.
With a radioactive source emitting alpha and beta radiation it might be possible to use two ion drives; one ejecting the positively charged alpha particles and the other ejecting the negatively charged beta particles. That way you won't build up a total charge in the craft. Plus, there won't be any charged cloud tracing the craft since the sum total charge of the ejecta is zero.
Though apparently, the NASA people WANT to build up a charge... Meh.
All rites reversed 2010
Don't you mean, "The Non-Planet Formerly Known As Pluto"?
There exists another interesting invention around about the same principles. This one however uses solar wind, not magnetic fields, is steerable and able to work itself against the solar wind by adjusting the polarity and charge of the individual wires. They are apparently doing practical research on this right now. A short english description can be found at http://www.electric-sailing.fi/index.html