Deceleration of high-velocity interstellar photon sails into bound orbits at $α$ Centauri

Abstract: At a distance of about 4.22 lightyears, it would take about 100,000 years for humans to visit our closest stellar neighbor Proxima Centauri using modern chemical thrusters. New technologies are now being developed that involve high-power lasers firing at 1 gram solar sails in near-Earth orbits, accelerating them to 20% the speed of light (c) within minutes. Although such an interstellar probe could reach Proxima 20 years after launch, without propellant to slow it down it would traverse the system within hours. Here we demonstrate how the stellar photon pressures of the stellar triple $\alpha$ Cen A, B, and C (Proxima) can be used together with gravity assists to decelerate incoming solar sails from Earth. The maximum injection speed at $\alpha$ Cen A to park a sail with a mass-to-surface ratio ($\sigma$) similar to graphene (7.6e-4 gram/m$^{-2}$) in orbit around Proxima is about 13,800 km/s (4.6% c), implying travel times from Earth to $\alpha$ Cen A and B of about 95 years and another 46 years (with a residual velocity of 1280 km/s) to Proxima. The size of such a low-$\sigma$ sail required to carry a payload of 10 grams is about 10$^5$ m$^2$ = (316 m)$^2$. Such a sail could use solar photons instead of an expensive laser system to gain interstellar velocities at departure. Photogravitational assists allow visits of three stellar systems and an Earth-sized potentially habitable planet in one shot, promising extremely high scientific yields.