Normal forced to point away from sun. Cosine-squared thrust magnitude.

I made a change to the solar sail module. If the normal vector has a sun-facing component, it is negated to force it to point away from the sun, so that the backside of the sail produces thrust in the correct direction.

I also changed the magnitude of the force to the cosine-squared of the angle to the sun. One cosine term accounts for the sunlight intercepted by the sail as it turns. The second cosine term is because the sun strikes the sail at an angle, and not all of it's momentum is transferred. The result is that maximum sideways thrust (useful for orbit maneuvers) is generated at 35 deg to the sun, not 45 deg.