The general idea is that white holes don't exist. Why? They don't seem to lose much mass while they aren't feeding. They actually do lose mass, supposedly by Hawking's Radiation (may not be exact name) by which matter is radiated, suprisingly on this "side" though keep in mind I'm somewhat rusty on this subject. About solar sails, you can use them to change your orbit. For example, angle it so that you speed up relative to the sun, you'll go higher. Angle it so you slow down, and you'll "fall" even though you're thrusting away. Like I said in the other thread, it all depends on orbits