This is the plan-view (looking down on the ecliptic) companion to the 3D solar-sail
simulator — same equations of motion, drawn in 2D so the spiral geometry and the trail's
curvature are easy to read directly, plus a live specific-orbital-energy readout that makes
the outward/inward pumping caused by the sail's pitch visible as a number, not just a shape.
F_photon = (2·S·A·cos²α) / c (S = solar flux at current radius)
S(r) = S₀ · (r₀/r)²
a_tangential = F_photon·sin(α) / m → changes specific orbital energy ε → spiral in/out
ε = v²/2 − GM/r
- Sail pitch angle α — tilts the sail; positive angles add energy (spiral outward), negative angles remove it (spiral inward), α=0 gives pure radial push with no spiral.
- Sail area — larger reflective area intercepts more photons, scaling thrust linearly.
- Craft mass — heavier craft accelerates more slowly for the same thrust.
- Time acceleration — speeds up the simulation so orbital drift becomes visible in seconds instead of years.
- Reset orbit — returns the craft to a circular 1 AU starting orbit.
- Trail — toggles the fading path trace so you can compare successive loops.
Real-world relevance: missions like JAXA's IKAROS and The Planetary Society's LightSail have
demonstrated exactly this photon-pressure steering to change orbits without any propellant.