Great ideas fan out in unexpected directions, which is why James Bickford now looks at antimatter in a new light. Bickford (Draper Laboratory, Cambridge MA) realized that an adaptation of Robert Bussard’s interstellar ramscoop might have its uses in collecting antimatter. The concept grew out of the realization that antimatter sources were available not only near the Earth but farther out in the Solar System, where antiparticles could be collected and used to boost spacecraft initially to speeds of 100 kilometers per second. That’s sufficient for interstellar precursor missions outside the heliosphere, including the possibility of getting a payload to the Sun’s gravitational focus, where a new kind of space-based astronomy waits to be exploited.
Refine the process enough and you start talking about even greater speeds through more efficient antimatter collection, one great benefit being that instead of producing the stuff in Earth-bound particle accelerators, you’re actually mining natural supplies. Bickford was kind enough to pass along his complete final report for NASA’s Institute for Advanced Concepts (NIAC), one of the last projects funded by that agency as it encountered the kind of budgetary crises familiar to deep space researchers and closed. It’s a fascinating document that I want to discuss over several days this week (though perhaps not consecutively, because we’re about to get some interesting exoplanet news).
Before we get into collecting it, ponder the beauties of antimatter itself. The annihilation of a particle with its antiparticle liberates the entire rest mass of each as energy. Indeed, the process is so spectacular — ten orders of magnitude greater than chemical reactions, and between 102 to 103 more efficient than nuclear — that antiprotons on the order of tens of nanograms might be sufficient to reach the 100 km/sec velocities mentioned above. Clearly, larger quantities of antimatter expand the options enormously, offering higher speeds still up to the relativistic velocities needed for interstellar missions.
Bickford’s numbers on antimatter’s potential further drive the point home. The annihilation of a single kilogram of antimatter releases the energy equivalent of thirty million barrels of oil. If you work out worldwide energy production per year in these terms, you find that the total is equivalent to 2200 kg of antimatter. Contrasting sharply with antimatter’s potential, however, is the price. Using the methods available today, which rely on extracting antimatter from sub-atomic collision debris in accelerators, the worldwide output is in the low nanogram per year range. The cost: an estimated $100 trillion per gram, give or take a few megabucks.
That’s one reason that antimatter propulsion concepts have taken a sharp turn toward the realistic after heady earlier speculations. Antimatter Catalyzed Microfission/Fusion, which uses antiprotons to trigger a efficient form of nuclear fission, has been extensively studied at Pennsylvania State University, showing potential for interplanetary missions (Mars becomes reachable in about 45 days). And ACMF is, as it has to be, stingy with the antimatter, requiring only nanogram quantities. Steven Howe examined a variant of this approach in an earlier NIAC study, while Gerald Jackson produced a NIAC study on harvesting antimatter that would factor into Bickford’s later analysis.
Can we think about getting antimatter up to the microgram level? With ten micrograms of antiprotons, we can envision a 100-ton payload on a one-year round-trip mission to Jupiter. But how do we go about producing antimatter at this level, and where is the best place to produce it? In my next post on Bickford’s work, I want to contrast current production methods with the antimatter ‘harvesting’ option and explain why our own Solar System may serve as a renewable source of the fuel we need once we can build the infrastructure necessary to collect and deploy it. We’ll talk about these and other issues soon, and also discuss what technologies will have to reach an appropriate readiness level before we can put an efficient antimatter collector into operation.