"Alex Terrell" wrote:
Please don't misintepret me. I do "believe" in solar sails. I'm just
trying to figure out how it works, because, in the normal world:

Momentum = mass * velocity

If mass = 0 and velocity = 3E8, then momentum = 0

Please tell me what I'm missing?

This is one of the cases where you have to remember that
"mass" is really "rest-mass" but in this case rest-mass
is the wrong mass, so you want something more like the
old "relativistic mass".

In other words, you're missing that e=mc^2, and that
since photons have energy they also have mass (and
momentum).