Photon-Sail Equilibria in the Alpha Centauri System

Abstract

Our closest neighboring star system, Alpha Centauri, is located at “mere” 275,000 astronomical units (au) from Earth. Because of its “close proximity” to Earth, Alpha Centauri is often considered as the prime target for a future interstellar exploration mission [1]. It holds significant scientific importance for better understanding our sun, and stars in general, and for advancing our knowledge on the formation and evolution of the solar system [2]. Moreover, by visiting Alpha Centauri, Earth-like exoplanets may be discovered (in addition to the discovery of Proxima Centauri b in 2016 [3]). Voyager 1, our fastest and farthest spacecraft, 146 au from the sun at the time of writing, would take approximately 75,000 years to reach Alpha Centauri. Photon-sail propulsion could substantially reduce this travel time [4] even though it exclusively makes use of the radiation pressure from a star to drive the spacecraft forward [5]. This novel propulsion technology has made significant technological progress in recent years through JAXA’s IKAROS mission, NASA’s NanoSail-D2 mission, and the LightSail-1 and LightSail-2 missions by the Planetary Society. Continued technological advancement will be achieved through other proposed and scheduled missions such as NASA’s NEA Scout mission [6]. Proposals for using photon sails to reach targets far beyond our solar system are not new (see, e.g., Refs. [4,7]), and initiatives with clear goals of reaching Alpha Centauri within a generation are underway, e.g., the Breakthrough Starshot project.§ However, little is known about the dynamics of the photon sail once it arrives in the other star system, especially in a multistar system like Alpha Centauri. To date, the only works investigating these dynamics include Refs. [8,9]. Both articles focused on the dynamics in the binary-star system composed of the stars Alpha Centauri A and B, and investigated the possibility of decelerating the spacecraft after arrival, assuming a graphene-based sail covered with a highly reflective coating. The MIRA Collaboration focused on the computation of artificial equilibria (AE) in the same binary-star system, but for a photon-balloon spacecraft, before investigating capture and transfer trajectories for a photon-sail propelled spacecraft in the elliptical restricted three-body problem (ER3BP) [2,10].