I can see where the confusion would come in, E1… the terminology is similar. Now, the solar wind, as we all know, is hydrogen nuclei, free electrons, and various and sundry other particles, all of which have mass. The photons, on the other hand, DO have zero REST mass, which is why they travel at lightspeed. Photons, however, also have non-zero RELATIVISTIC mass, which is how they come to have momentum, which can be transferred to other objects and how you can get useful work out of them.
Now, you can get useful thrust out of them both… but, as Niven and Pournelle pointed out in ‘The Mote in God’s Eye’, you can’t tack against the solar wind. It STICKS to your lightsail, and you can’t reflect it as you can with light. You can tack against the light coming from a star, and that in part is how you’d maneuver a lightsail craft.
This excerpt, taken from this site might clear things up. To wit:
—In consideration of the physics behind the sail a common misconception is that the propulsive force is provided by the solar wind.
The solar wind is a stream of charged particles, mostly high velocity electrons and protons, emanating from the solar corona. It is a
highly dynamic phenomenon, influenced by factors such as solar flares and X-ray bursts. The energy attatched to these particles
however is several orders of magnitude smaller than the energy attatched to the flux of solar photons itself (9x10-6 newtons for each
m2 of sail).
Hence the lightsail makes use of the solar photon flux for propulsion. While photons have no rest mass, they do of course have mass
while in motion, and thus momentum. Upon collision with the reflective sail material the photon will be reflected and, in the process,
apply a force to the sail. The size of the total force on the body of the craft will thus be proportional to the sail’s area.
The applied force can be directed by tilting the sail with respect to the incoming photon flux, this will change the direction of the
acceleration applied to the sail and thus allow changes in the sail’s orbit.
There’s much more at that site, which I commend to your attention…
Someday we’ll look back on this, laugh nervously, and change the subject…