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.