Sample return from Mercury and other terrestrial planets using solar sail propulsion

A conventional Mercury sample return mission requires significant launch mass due to the large AV required for the outbound, and return trips and the large mass of a planetary lander and ascent vehicle. It is shown that solar sail spacecraft can be used to reduce lander mass allocation by delivering the lander to a low, thermally safe orbit close to the planetary terminator. In addition, the ascending node of the solar sail spacecraft parking orbit plane can be artificially forced to avoid out-of-plane maneuvers during ascent from the planetary surface. Propellant mass is not an issue for spacecraft with solar sails, and so a sample can be returned relatively easily without resorting to lengthy, multiple gravity assists. A 275-m(2) solar sail with a sail assembly loading of 5.9 g/m(2) is used to deliver a lander, cruise stage, and science payload to a forced sun-synchronous orbit at Mercury in 2.85 years. The lander acquires samples and conducts limited surface exploration. An ascent vehicle delivers a small cold-gas rendezvous vehicle containing the samples for transfer to the solar sail spacecraft. The solar sail spacecraft then spirals back to Earth in 1 year. The total mission launch mass is 2353 kg, launched using a Japanese H2 class launch vehicle, C-3 = 0. Extensive launch date scans have revealed an optimal launch date in April 2014 with sample return to Earth 4.4 years later. Solar sailing reduces launch mass by 60% and trip time by 40%, relative to conventional mission concepts. In comparison, mission analysis has demonstrated that solar-sail-powered Mars and Venus sample returns appear to have oily modest benefits in terms of reduced launch mass, at the expense of longer mission durations, than do conventional propulsion systems.