Tomorrow is the scheduled launch of Cosmos 1 the first solar sail craft humans have put into space. It will be fired into orbit by a Russian sub. Then it will deploy solar sails and ground controllers will see whether thy can tack on the solar wind.
The Christian Science Monitor covers the nuts and bolts and some speculation but for me at least the real excitement is in what amounts to a ferry service to Mars and beyond. A solar sail powered craft which never slowed down could use the Martian and Earth gravity wells to change direction. Outbound the craft would accelerate, inbound it would furl its sails and coast. Do that a few times and you would have a craft flying very fast indeed.
The point is that the craft would have a constant acceleration towards Mars and that acceleration would be increasing with each round trip. And with each round trip the time it took to reach Mars (ignoring obital issues) would be reduced. Years ago Robert Heinlein pointed out that a craft with a constant acceleration of 1/10 of Earth's gravity could reach Mars in ten days.
Now, obviously, ther would be the small matter of catching the interplanetary ferry. But designing interception trajectories which called for a brief moment of high acceleration near the Earth end of the loop is not impossible.
At the moment, the scale of the Cosmos 1 project is minimal. 50 foot sails, a two hundred pound payload; but there is no reason in principle why this could not be radically expanded so that the sails would be on the order of several miles across and capable of pulling along fairly massive objects.
The key thing here is the understanding that if the ferry to Mars was going by every month or so (and there were three of them) there would be no need to send all the equipment needed for Mars exploration in a single shot. It would be quite possible to set up an orbiting supply dump and stock that up before ever setting foot on Mars.solar sailing