Fusion Propulsion Constraints Required by Robust Exoplanet Exploration

<ns3:p>Robust exoplanet exploration requires deceleration and orbital insertion, first around the target star, and ultimately around the exoplanet itself. Even for the nearest star Proxima Centauri, voyage durations under a century require spacecraft velocities of at least a few percent of the speed of light. There are few deceleration mechanisms feasible for such small stars. The propulsion system should optimally have a mass comparable to the scientific instrumentation. Nuclear fusion-based propulsion systems are one candidate technology. This paper reviews some of the physics constraints of such systems and reviews some promising fusion fuels such as helium-3 to assess their utility in an interstellar propulsion system.</ns3:p>