Deep Space Propulsion via Magnetic Fields

by Paul Gilster on May 22, 2007

The beauty of magnetic sail concepts — magsails — is that they let us leave heavy tanks of propellants behind and use naturally occurring phenomena like the solar wind to push us where we’re going. Solar sails, of course, do the same thing, though they use the momentum imparted by photons rather than the energetic plasma stream of the solar wind. And Cornell University’s Mason Peck is now suggesting another kind of mission that leaves the fuel behind. Instead of using the solar wind, it taps magnetic fields like those around the planets.

As we’ll see in a moment, we might one day use this method to send a fleet of micro-probes to Proxima Centauri. But let’s examine it first in light of planetary missions, which is what Peck has in mind with his Phase II NIAC study “Lorentz-Actuated Orbits: Electrodynamic Propulsion Without a Tether.” What the researcher is proposing is that a spacecraft can be made to accelerate in a direction perpendicular to a magnetic field. We know from Cassini images how the orbits of dust particles in Saturn’s rings are governed by such forces.

In fact, this ‘Lorentz force’ proves to be tremendously useful in the near-planetary environment. A spacecraft in Earth orbit, for example, creates a charge as it moves through the plasma surrounding the planet. The charge is minute, but it can be boosted either by emitting charged particles from a high-energy beam, or by using a lightweight surface (Peck suggests a thin, cylindrical wire mesh) to house a greater charge. Once charged sufficiently, the spacecraft will be deflected by the planetary magnetic field in a direction perpendicular to the magnetic field lines.

Jupiter’s magnetic field, containing fully 18,000 times the energy of Earth’s magnetosphere, would be ideal for this kind of work, offering plentiful opportunity not just for orbital adjustment but even for ‘hovering’ in place over a particular area to be studied (Robert Forward used to discuss doing something like this with ‘statites,’ satellites that would use solar sails to hover in Earth polar orbit or elsewhere). And imagine the increased payload that could be added to a Galileo-style spacecraft to Jupiter without the 371 kg of propellant that flew aboard that mission!

But the notion really opens up when you begin considering much smaller vehicles. Here I’m going to quote our own Larry Klaes, who wrote Peck’s work up for Ithaca (NY’s)’s Tompkins Weekly:

[Peck] notes that the concept might be ideal for small spacecraft. Cornell graduate student Justin Atchison is developing a satellite that is the size and heft of a single wafer of silicon.

“At this small scale, a spacecraft might be surprisingly susceptible to Lorentz force effects,” explains Peck. “But rather than launching just one of these ‘ChipSats,’ NASA might launch millions of them that would act as a swarm of very small sensors to detect life on another planet, provide communications, or serve as a distributed-aperture telescope many kilometers in diameter.”

As we move into the realm of ChipSats, Peck has my full attention. Take the ChipSat to its logical conclusion and you can envision thousands of tiny spacecraft slung out from the Solar System at ten percent of lightspeed to make the journey to the Centauri stars. “When these small craft arrive,” says Peck (I’m quoting from Larry’s story again), “they might send back a single, simple signal; one bit of information confirming or denying some scientific principle, such as is there a blue-green planet, for example.”

Peck’s completed Phase I study for NIAC is here, and you can read a precis of the Phase II project as well. Compared to solar sails or tether concepts, the Lorenz-Actuated Orbit (LAO) offers singular benefits. Peck writes:

“Electrodynamic tethers and solar sails certainly have their place. Tethers are convenient for deorbiting spacecraft in a passive way (i.e. without applied power). Solar sails work just as well, if not better, outside the geomagnetic field as they do near the earth. However, both suffer from the problem that the very large structures involved can deform under the action of the forces on them, reducing their performance. In the case of a tether, it appears that only gravity-gradient balance or spinning will help align a tether stiffly enough for it can raise an equatorial orbit in a mass-efficient way without buckling, tangling, or becoming redirected into a useless orientation. Solar sails are virtually impossible to reorient in an agile fashion. Our goal is to develop the LAO concept to the point where it is highly compact but offers the same propellantless benefits. The result will be an agile propellantless spacecraft. Even if the LAO spacecraft includes a long wire for capacitance, this wire will result in the same effect regardless of its direction. This significant advantage argues for the continued investigation of the LAO concept and suggests that it may prove more readily adaptable to existing mission architectures than are tethers.

You can read more about the concept at Peck’s site, and the issue of the Tompkins Weekly with Larry Klaes’ article is here. I’m also reminded of Robert Freitas idea of the ‘needle probe,’ an interstellar vehicle the size of a sewing needle but equipped with the nanotechnological tools to create an observing station out of raw materials it finds in the planetary system to which it is sent. Send not one or two but thousands of these for redundancy and you open up the nearby stars to minute examination. Will ChipSats offer a way to put instrumentation into Centauri space and beyond?

Addendum: I had originally referred to “Jupiter’s magnetic field, fully 18,000 times stronger than Earth’s…,” which Paul Dietz points out in the comments below is a mis-statement, as now corrected above.

Paul Dietz May 22, 2007 at 16:09

Jupiter’s magnetic field is not 18,000 times stronger that Earth’s. It occupies a much larger volume, but the field strength at the surface is only a few times that of Earth’s at its surface.

Administrator May 22, 2007 at 16:21

Whoops — misstated indeed. I’ll stick in an addendum at the end of the piece correcting same. Thanks, Paul.

Darnell Clayton May 22, 2007 at 18:39

The more I look at magsails, the more I fall in love with them!

Not only do they provide a simple, yet elegant way to propel a craft around our solar system (and beyond), but potentially they can protect us from deadly radiation from the sun.

The hardest part of course is actually getting these objects into orbit, although if SpaceX can make chemical rockets cheaper (either that or someone can build a space elevator or maglauncher) then we may yet see these star crafts in our distant future.

Administrator May 22, 2007 at 19:58

That problem with getting to LEO is thorny indeed, but it’s great to see the commercial interest in solving it. Cheap access to orbit will change so many things… As for magsails themselves (and here I’m talking about Winglee’s concept), yes, they’re simple, elegant and hold huge promise. Couple them with beamed propulsion concepts and you get into some serious deep space mission possibiities.

Jonathan Burns May 22, 2007 at 20:04

It’s intriguing to combine Peck’s concept with Devon Crowe’s kilometer-scale metal-filmed space bubbles. The capacitance of one of those would be awesome. Of course, so would the potential gradient around any rupture :-( And the catch with planetary magnetosphere usage is that micrometeors are plentiful just where the field is strong.

Will read Peck’s paper shortly. Thanks!

Jack William Bell May 23, 2007 at 2:21

Note: Your trackback URL is failing! I’m doing it by hand instead…

Trackback: F = q(E + v * B) where F means “Hello Jupiter”

Centari Dreams has an interesting post on using planetary magnetic fields to accelerate spacecraft. How does this work? By leveraging something called Lorentz force…

Michael Thomas September 24, 2007 at 10:40

The researcher is thinking outside the box. Its better to advance an idea
that fails than to never try. Space is our only possibility with so many
unknowns we need to overcome atleast so some limited understanding.

Maybe if someone could ever solve the unified field theory we would
understand more.

ljk December 7, 2007 at 10:26

Enhancing magnetic sail launches using Light weight high volume magnet production

In theory, it is possible for a magnetic sail to launch directly from the surface of a planet near one of its magnetic poles, repelling itself from the planet’s magnetic field. However, this requires the magnetic sail to be maintained in its “unstable” orientation. A launch from Earth requires superconductors with 80 times the current density of the best known high-temperature superconductors.

Other magnetic launching systems tend to use stronger magnets and shorter launch systems.

Earth’s magnetic field is about 60 microtesla at the poles.

Compared to the skyhook, which is just barely possible with even the theoretical best material properties, a tower 100 km high is easy. Flawless diamond, with a compressive strength of 50 GPa, does not even need a taper at all for a 100 km tower; a 100-km column of diamond weighs 3.5 billion newtons per square meter, but can support 50 billion. Even commercially available polycrystalline synthetic diamond with advertised strengths of 5 GPa would work. Of course in practice columns would be tapered so as not to waste material; and the base of the tower would be broadened to account for transverse forces, such as the jet stream. Only the bottom 15 km (i.e. 15%) of the tower lies in the troposphere and would have to be built taking weather into account.

Full article here:

http://advancednano.blogspot.com/2007/12/enhancing-magnetic-sail-launches-using.html

ljk May 23, 2008 at 15:07

Experimental Study of a Lorentz Actuated Orbit

Authors: William R. Gorman, James D. Brownridge, Mason Peck

(Submitted on 21 May 2008)

Abstract: This experimental study investigates a new technique to keep a satellite in orbit utilizing electrodynamics. The technique consists of establishing a charge on a satellite such that the body’s motion through a planetary magnetic field induces acceleration via the Lorentz force.

In order to find the relationship between capacitance and power required to balance incident plasma current, various objects were tested in high vacuum, plasma, and Xenon gas to determine their ability to hold charge. Radioactive material (Am-241) and pyroelectric crystals were tested as a candidate power source for charging the objects. Microscopic arcing was observed at voltages as low as -300 V. This arcing caused solder to explode off of the object. Insulating the object allowed the charge to remain on the object longer, while in the plasma, and also eliminated the arcing. However, this insulation does not allow a net charge to reside on the surface of the spacecraft.

Comments: 4 pages, 3 figures, work from thesis

Subjects: Plasma Physics (physics.plasm-ph)

Cite as: arXiv:0805.3332v1 [physics.plasm-ph]

Submission history

From: William Gorman [view email]

[v1] Wed, 21 May 2008 19:24:15 GMT (171kb)

http://arxiv.org/abs/0805.3332

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