Payload mass fraction optimization for solar cargo missions

SOLAR sailing offers the potential to reduce the required initial mass in low Earth orbit for future piloted Mars missions.1¡3 Athough solar sailing does not appear to be suitable for crew transport, it can be an extremely efŽ cient mode of propulsion for the transport of logistics in support of a human crew. This may include premission caching of logistics and/or resupply missions to support long-duration surface stays. Because solar sails do not require reaction mmass, a single solar sail may, in principle, be used for multiple Earth-Mars-Earth round trips. The limit to the number of round trips that can be made by a single solar sail will be dictated largely by the lifetime of the sail Ž lm in the space environment. Previous studies of the solar sail cargo mission problem have considered either point designs1 or have considered speciŽ c launch opportunities.2 However, a key question that arises when considering the use of solar sails for round-trip logistic supply missions is the optimum payload mass fraction of the solar sail. As the payload mass fraction of the solar sail is increased, a greater payload mass is delivered, but the trip time will also increase. Similarly, as the payload mass fraction of the solar sail is decreased, a smaller payload is delivered, but with a shorter trip time. The payload mass fractionthat is selectedshould, therefore,be chosento balancethese two effects and maximize the mean rate of payload mass transfer to Mars.