Evaluation of solid-core thermal antimatter propulsion concepts

Energy released during antimatter annihilation can be used to heat a working fluid to directly produce thrust (an “antimatter rocket”) or run a thermodynamic cycle to generate power for conventional electric propulsion systems (antimatter power generation). For a solid reactor core, we evaluate and compare such antimatter propulsion concepts and assess the resulting performance for different propellants (hydrogen, water, methane, and carbon dioxide) and electric propulsion technologies (arcjets, Hall thrusters, and gridded ion thrusters). In contrast to positron–electron annihilation (which only produces gamma rays), complete stopping of relativistic pions released during antiproton–proton annihilation increases the required reactor core size by approximately an order of magnitude, resulting in significantly larger propulsion systems. Because of reactor core material considerations, the maximum temperature and specific impulse achievable in antimatter rockets is limited. By instead operating the core at a lower temperature to drive a closed thermodynamic Brayton cycle, antimatter power generation can run electric propulsion systems with higher specific impulses. Although this reduces the propellant mass needed for a given mission, the combination of thermodynamic cycle efficiency (around 30%) and electric thruster efficiency (typically between 30%–70%) increases the antimatter mass required by one to two orders of magnitude. The lower thrust of electric propulsion systems also leads to longer burn and maneuver times. Considering emerging industry trends, the use of renewable propellants offers large potential benefits to future antimatter propulsion systems that can refuel in space.