Solar Sail Trajectory 2D: Photon-Pressure Orbital Steering

This is the 2D companion to the 3D solar-sail simulator: the identical photon-pressure and two-body-gravity equations of motion, integrated in plan view instead of orbited around in a 3D scene. Sunlight intensity falls off as the inverse square of distance, a tilted reflective sail turns a fraction of that momentum flux into thrust, and the component of that thrust along the direction of travel pumps orbital energy in or out depending on the sign of the pitch angle — visible here as a spiral trail winding outward or inward around the sun, alongside a live specific-orbital-energy readout that turns the same physics into a number you can watch cross zero (an escape trajectory) or climb toward a tighter bound orbit.