  It is shown that the curvature of spacetime, a possible net electric charge
on the sun, a small positive cosmological constant and the oblateness of the
sun, in conjunction with solar radiation pressure (SPR), affect the bound
orbital motion of solar sails and lead to deviations from Kepler's third law
for heliocentric and non-Keplerian orbits. With regards to the Lense-Thirring
effect, the SRP increases the amount of precession per orbit for polar orbits.
Non-Keplerian polar orbits exhibit an analog of the Lense-Thirring effect in
which the orbital plane precesses around the sun.
