Comment Re:Spacecraft can have solar sails (Score 1) 183
The first person to think of the concept of solar sails was Johannes Kepler in 1610, when he observed that comets' tails always pointed directly away from the sun and speculated that whatever force caused that could be harnessed by sails. Konstantin Tsiolkovsky in 1921 made the first serious proposal, with the concept of light pressure being fairly well-understood at that point.
As far as Star Trek is concerned, I might point out that while TOS never had solar sails, Deep Space Nine did entire episode centered around a solar sail vessel ("Exploters").