Maneuvering Interstellar Light Sails
The discovery of Proxima b, a roughly Earth-mass planet (Anglada-Escudé+ 2016) in the stellar habitable zone around our closest stellar neighbor (Proxima Centauri, α Cen C) has recently excited humanity’s vision of interstellar travel. Earlier studies involved laser-pushed light sails with masses of several tons and sail areas of some square kilometers. Advances in ultra lightweight material research (Mecklenburg+ 2012), highly reflective solar sail design (Scheffer 2015), and the development of ultracompact electronic devices have now shifted the focus to ultrathin and highly reflective gram-scale photon sails (Lubin 2016; Heller+ 2020). With an intended speed of 20% of the speed of light, however, these photon sails would traverse the Earth-Moon distance in just about six seconds, with little time left for high-quality close-up exploration, for example of Proxima b. We find that the stars α Cen A and B can be used as photogravitational swings to decelerate an incoming light sail and deflect it into a bound orbit around Proxima (Heller & Hippke 2017). Our numerical simulations of the photon pressure and the gravitational force in the α Cen A, B, and C triple system show that an autonomous photon sail could be maneuvered through the system and into a bound orbit without the need for onboard fuel. We also derive the minimum travel times to other nearby stars under the assumption that the respective stellar luminosity be used for deceleration into a bound orbit (Heller+ 2017). Beyond technological considerations, the applicability of interstellar light sails depends on the aiming accuracy of the outbound trajectories and the precision to which the target coordinates and proper motion are known.
