Ultrafast transfer of low-mass payloads to Mars and beyond using aerographite solar sails

Abstract

With interstellar mission concepts now being under study by various space agencies and institutions, a feasible and worthy interstellar precursor mission concept will be key to the success of the long shot. Here we investigate interstellar-bound trajectories of solar sails made of the ultra lightweight material aerographite. Due to its extremely low density (0.18kg m−3) and high absorptivity (A∼1), a thin shell can pick up an enormous acceleration from the solar irradiation. Payloads of up to 1kg can be transported rapidly throughout the solar system, e.g., to Mars and beyond. Our simulations consider various launch scenarios from a polar orbit around Earth including directly outbound launches as well as Sun-diver launches towards the Sun with subsequent outward acceleration. We use the poliastro Python library for astrodynamic calculations. For a spacecraft with a total mass of 1kg (including 720g aerographite) and a cross-sectional area of 104m2, corresponding to a shell with a radius of 56m, we calculate the positions, velocities, and accelerations based on the combination of gravitational and radiation forces on the sail. We find that the direct outward transfer to Mars near opposition to Earth results in a relative velocity of 65km s−1 with a minimum required transfer time of 26d. Using an inward transfer with solar sail deployment at 0.6AU from the Sun, the sail’s velocity relative to Mars is 118km s−1 with a transfer time of 126d, where Mars is required to be in one of the nodes of the two orbital planes upon sail arrival. Transfer times and relative velocities can vary substantially depending on the constellation between Earth and Mars and the requirements on the injection trajectory to the Sun diving orbit. The direct interstellar trajectory has a final velocity of 109km s−1. Assuming a distance to the heliopause of 120AU, the spacecraft reaches interstellar space after 5.3yr. When using an initial Sun dive to 0.6AU instead, the solar sail obtains an escape velocity of 148km s−1 from the solar system with a transfer time of 4.2yr to the heliopause. Values may differ depending on the rapidity of the Sun dive and the minimum distance to the Sun. The mission concepts presented in this paper are extensions of the 0.5kg tip mass and 196m2 design of the successful IKAROS mission to Venus towards an interstellar solar sail mission. They allow fast flybys at Mars and into the deep solar system. For delivery (rather than fly-by) missions of a sub-kg payload, for example medical supply or replenishment of essential materials, the biggest obstacle remains in the deceleration upon arrival.