Concepts, Problems, & Opportunities for use of Annihilation Energy:

An Annotated Briefing on Near-Term RDT&E to Assess Feasibility

RAND Note N-2302-AF/RC

B. W. Augenstein

ANTIMATTER PROPULSION SYSTEMS

Chart showing Isp for various antimatter systems and missions

Some illustrations are now discussed to put antimatter usage intoperspective. The illustrations consider propulsion applications earlieralluded to on Slide 5, as the chart shows.⁴

Because of the very high energy density of antimatter, a simpleoptimization analysis can be made which minimizes the amount ofantimatter needed as a function of the mission characteristic velocity,V_m. We find that the minimum antimatter consumption arises when wechoose the exhaust velocity, V_e to be ~ 0.63 V_m; and that minimumconsumption is then ~ a M_e V_m²/C² , where a is a constant we can takeusually roughly between l/2 and 1, M_e is the vehicle empty mass (M_e = payload mass + inert mass), and C = light velocity. To take a specificexample from the chart, if we wish to have M_e = 1 metric ton for thedouble reverse orbit mission from a space station (a vehicle leaves thestation to contact a counter-orbiting vehicle, and returns), theantimatter consumption is of the order of 5-10 mg. The optimizationanalysis in effect assumes that the exhaust velocity V_e is "tailored" tofit the necessary V_m . This I_sp tailoring is possible, to a certainextent, using available conceptual engine designs, and the analysis thenholds reasonably well up to V_m ~ ½ C. If we fix I_sp then operationoff this optimization can result in somewhat more than necessaryantimatter consumption, but lower mass ratios than the "optimal" valueof ~ 4.9 ( = e^V_m/V_e). The chart shows a case of this.

Possible engine design types are visualizable over an enormousrange of I_sp. The relative merits of using antimatter of courseincrease dramatically when more demanding missions than those shown onthe chart are considered. Many engine designs and other potentialapplications rest on good understanding of annihilation phenomenology,an example of which occurs in the next few pages. Many interestingtheoretical and computational issues arise in further developing thisunderstanding.

⁴Further details are found, for example, in: AntiprotonAnnihilation Propulsion, R. Forward, AFRPL-TR-85-O34, 15 August 1985;and Some Examples of Propulsion Applications Using Antimatter, B.Augenstein, The Rand Corporation, P-7113, July 1985.