A preview of space-flight issues of the future: how do you account for the effects of relativity when travelling long distances? A solar sail launched from close to the Sun would have to account for relativistic effects when navigating to the edges of the solar system:
And even though those effects are relatively minor to start with, they have a significant effect over long distances.
The calculations carried out by Kezerashvili and Vazquez-Poritz show that the effects of general relativity could push a solar sail off course by as much as a million kilometers by the time it reaches the Oort Cloud
The promise of solar sails as a propulsion mechanism is impressive:
By one calculation, a solar sail with a radius of about a kilometer and a mass of 300 kg (including 150 kg of payload) would have a peak acceleration of about 0.6 g if released on a parabolic trajectory about 0.1 astronomical unit (AU) from the sun (where the radiation pressure is higher).
That kind of acceleration would take it beyond the Kuiper belt to the heliopause, the boundary between the solar system and interstellar space (and a distance of 200 AU), in only 2.5 years.
In 30 years, a solar sail could travel 2,500 AU, far enough to explore the Oort Cloud.
Of course we need to actually build one of these things first.