Can you "tack" a solar sail?
Niven/Pournelle had a cool idea in The Mote in God's Eye of charging your craft when traversing a magnetic field to change direction (not specific to sails, but another passive technique).
Niven/Pournelle had a cool idea in The Mote in God's Eye of charging your craft when traversing a magnetic field to change direction (not specific to sails, but another passive technique).