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If you're asking about interstellar travel, then the answer is pretty simple; For diffuse, unfocused sources of light like the one emitted by stars, photon flux density decreases with the inverse square of the distance to its source, and with it photon pressure (imparted momentum of absorbed or, better yet, reflected photons) on the sail. So you accelerate away from the Solar system on photon pressure of the Sun, and decelerate on photon pressure of the destination star as you get closer to it. That might involve rotating the whole sail the other way around at half point, but that's it.
For more local orbits though, things get a bit more interesting. One thing we need to consider is that wherever in the Solar system we are, we're already in orbit around something. We're always orbiting some gravity well. And to move from one orbital altitude to another, say, decreasing heliocentric orbital altitude from one of the Earth (average of 1 AU) to one of Venus (about 0.7 AU), or increasing it to one of Mars (1.5 AU) and so on, we have to either increase angular momentum to move into a higher one, or decrease it to move into a lower one. So you don't really require the sail to be accelerating directly towards the Sun to decrease your orbital altitude with respect to it. It's enough to slow your orbital speed and with it decrease your angular momentum, and the orbit will progressively shrink to a lower altitude one.
Yes, flipping the vessel around is an obvious solution. Now, think about how long it will take to slow down from interstellar velocities to interplanetary velocities and review this post:
Here all of you are being offered the opportunity to actually and essentially, run a search upon "How do you slow down as solar sail".
No. I said that slowing down is a problem. Flipping the sail around does not change that. Using an ion drive does not change that.
Or at the time were you too busy to look into it as you were too, busy to run a search on "How to slow down a solar sail?"
Thanks, and goodbye.
Ok, so the word moron comes to mind
Deceleration of High-Velocity Interstellar Photon Sails into Bound Orbits at α Centauri Using Photogravitational Assists
1 Max Planck Institute for Solar System Research, PLATO Data Center, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany, firstname.lastname@example.org 2 Luiter Straße 21b, 47506 Neukirchen-Vluyn, Germany 3 Unidad Mixta Internacional Franco-Chilena de Astronomía, CNRS/INSU UMI 3386 and Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile 4 LESIA (UMR 8109), Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 Place Jules Janssen, 92195 Meudon, France