A Provocative Antimatter Strategy

by Paul Gilster on May 23, 2006

Ponder how difficult current antimatter work is. We produce the stuff in our particle accelerators and rely on extracting antiparticles from collision debris. One in about 105 proton collisions actually produces an antiproton that can be collected. This is why we see figures like $62.5 trillion per gram (some estimates are even higher) for antiproton production costs. Not only that, but once we have created antimatter, we have to store it in a vacuum in magnetic/electric fields to keep it from any contact with normal matter.

All these are problems with using antimatter for propulsion. After all, it’s one thing to store tiny amounts of antimatter in bulky Earth-based traps, and quite another to scale storage up to protect the antimatter from annihilation for a period of months or years, not to mention the need to transport it into orbit for uses in space. But as James Bickford (Draper Laboratory, Cambridge MA) and team point out, antimatter creation and storage in space seems more straightforward. The interactions between high-energy galactic cosmic rays (GCR) and matter in the interstellar medium both produce and trap such antiparticles. Can we adapt this principle to space technologies?

Bickford has been studying for some time now a method of capturing and storing antimatter in a magnetic funnel, a tiny magnetosphere that would be generated around a spacecraft. In an e-mail to Centauri Dreams, the physicist elaborates:

“I believe you can store antiprotons (or positrons) in the magnetic scoop which I’ve proposed for capturing antiparticles produced naturally in the environment. During the collection process, the antiparticles can be transferred to closed field lines and stably trapped in the mini-magnetosphere that surrounds the spacecraft. Most of the issues traditionally associated with antimatter storage are not relevant in such a system. As a bonus, the field also acts as a radiation shield.”

It’s a shrewd insight, and one that Bickford has been developing in a recently completed project for NASA’s Institute for Advanced Concepts. Bickford considers the magnetosphere surrounding the Earth as a prime area for study, and in his work analyzes how antiparticles are produced and confined due to the nuclear reactions between those high-energy cosmic rays and elements of the atmosphere. His work proceeds with a look at the total supply of antiprotons that should surround not just the Earth but other bodies in the Solar System.

These investigations find that the Earth has a small trapped supply of antiprotons in the range of 0.25 to 15 nanograms which is steadily replenished. Saturn, on the other hand, should by the Bickford model generate perhaps 400 micrograms of antiprotons due to the interactions of GCRs and the ring system. So here’s just one creative concept: collect antiprotons near the Earth to propel a bootstrap mission, with the spacecraft proceeding on to Saturn for the bulk of its fuel. Find a way to produce still more antimatter and even more exotic missions become forseeable, about which more in a moment.

But let’s look first at the operation of that magnetic funnel, which would collect antiprotons in regions of high intensity local production. The technique would use high temperature superconducting loops to collect antiprotons, and would rely on a magnetic bottle formed from the same superconducting loops to store the particles. From a paper on this work that Bickford intends to present at this summer’s New Trends in Astrodynamics conference in Princeton:

We have proposed the use of a magnetic scoop to concentrate the antiparticles from the space environment. The concentrated flux can then be transferred to the mini-magnetosphere that forms around the scoop to store the antiparticles for long periods of time. A magnetic scoop placed in a low inclination orbit can be designed to intercept nearly the entire antiproton supply trapped in a planet’s radiation belt. The scoop can also be optimized to operate in deep space where it can trap portions of the background flux.

And again:

Particles and antiparticles at various energies can coexist in the same device since the large trapped volume (km3 or more) and natural vacuum afforded by the space environment minimizes losses.

Add to this another factor, that the natural supply of antiprotons could theoretically be augmented by a particle accelerator placed in orbit, removing the need for bulky ground storage and transport into Earth orbit. The large storage volumes available would allow the generating system to be placed within the antimatter trap, an efficient way to trap nearly all the antiprotons produced. Bickford figures a 100 kWe generator could produce roughly 10 micrograms per year; a 1 GWe source would allow 100 milligrams in the same period, a level, Bickford notes, so far above what is currently possible that it is “…sufficient to enable the first interstellar missions to nearby stars.”

Centauri Dreams‘ take: These ideas are remarkably productive, and should push antimatter research into new directions. We’ve examined the benefits of magnetic sail technology on many occasions, wedding it to solar wind propulsion and in some thinking to particle beams. Here is a way to use the natural properties of a magnetic scoop to both produce and house antimatter in workable amounts, and with reasonable hopes for success with technologies that will be coming into their own in the not so distant future (the biggest issue may be with superconductor performance, which will have to be improved significantly).

For more, see Bickford’s NIAC report. The preprint of the upcoming presentation is Bickford, Schmitt, Spjeldvik et al., “Natural Sources of Antiparticles in the Solar System and the Feasibility of Extraction for High Delta-V Space Propulsion,” as yet unpublished. We need further work on this persuasive and provocative concept.

{ 5 comments }

Colony Worlds May 23, 2006 at 19:40

It’s ironic, isn’t it? Whenever we come up with complex ideas for travel, technology, etc., we are humbled by what our surroundings teach us.

If we could indeed collect enough anti-matter to head towards Saturn, then it would make the trip a lot easier, not to mention safer via a magnetic field. I wonder if a similiar device could be used or modified for larger objects, such as asteroids or even a planet to provide an artificial magnetic field?

Sounds very interesting…thanks for the news info…every time I visit this site I feel a little bit closer towards actually seing “the final frontier.”

pfdietz May 24, 2006 at 18:45

The obvious place to put a very large antimatter factory is around Jupiter. You could inject the antiprotons into that magnetosphere, and you could generate power for the accelerator by putting an electrdynamic tether on one of the inner moons (Metis or Adrastea, say). Pulling a terawatt of poiwer from the tether would drop the orbit Metis about a kilometer per year, IIRC.

Administrator May 25, 2006 at 13:06

The electrodynamic tether coupled with Bickford’s mini-magnetosphere is a wonderful insight, and I second your idea about locating a factory in Jupiter space. Notions like these, which draw so beautifully on our observations of natural magnetic fields and their properties in the Solar System, give me hope that some of the more intractable problems with antimatter will eventually be solved. That final frontier Colony Worlds talks about above is one we all hope to see, and one of the great pleasures of editing this site is watching the insights come in from readers who study a news story and see its further implications.

Radu December 19, 2006 at 13:10

It seems obvious to me that any kind of “spaceship” that uses antimatter for propulsion must be able to produce it as needed. The very notion of “antimatter factory” is debatable in terms of costs.

The path to build nuclear reactors small enough to be fitted on a submarine should drive toward a small “antimatter reactor” which will fix some issues, mainly autonomy and storage.

Timothy J Mayes June 5, 2007 at 8:08

The kind of particle accelerator that can produce antimatter in the form of
antiprotons is also able to accelelerate protons to near the velocity of light .
We could simply use such an acclerator to accelerate protons to near the velocity of light: then neutralize them, and expell them to generate thrust,The use of the proton particle accelerators energy to do this would be thousands of times more efficient then using its energy to make antiprotons, and trap them .
tim

Comments on this entry are closed.

{ 3 trackbacks }