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PolskiPlanetary Gravity Exploration Dashboard (2D)
A top-down orbital-mechanics sandbox: a spacecraft orbits a planet under real Newtonian gravity while apoapsis, periapsis, eccentricity and orbital period are recomputed live from the state vectors β fire prograde or retrograde burns to raise, lower, or break the orbit.
The 3D original renders spacecraft, "deep space missions" and an "AI exploration hub" as decorative Three.js groups that spin on a timer β there is no gravity, no trajectory and no orbit anywhere in that scene, despite the title promising one. This 2D companion builds the actual mechanic the title describes: a single spacecraft point-mass orbiting a planet under Newton's inverse-square law, integrated with a fixed-step symplectic scheme so the orbit stays closed instead of drifting from numerical energy leakage. A side panel exposes the planet's gravitational parameter, the craft's starting altitude and speed (as a multiple of the local circular velocity) and a time-scale slider, while prograde and retrograde burn buttons let you fire real delta-v along the current velocity direction β watch the opposite side of the orbit rise or fall exactly as it would for a real orbital maneuver. Apoapsis, periapsis, eccentricity and orbital period are recomputed every frame straight from the position and velocity vectors using the vis-viva equation and the eccentricity vector, so pushing the orbit past e = 1 flips the readout to an open escape trajectory instead of a closed ellipse.
2D orbital-mechanics lab: real inverse-square gravity, a fixed-step symplectic integrator, live apoapsis/periapsis/eccentricity/period readouts derived from the vis-viva equation, and prograde/retrograde delta-v burns.
2D Β· HTML5 Canvas 2D Β· 60 FPS target Β· runs fully client-side, no install
β Frequently Asked Questions
Q: Why does a prograde burn raise the far side of the orbit instead of the near side?
A: Adding energy at one point in an orbit raises the altitude on the opposite side β the point you burn at stays fixed as the new periapsis or apoapsis, while the far side moves. This is exactly how real Hohmann transfer maneuvers work.
Q: What does eccentricity actually measure here?
A: It is the magnitude of the eccentricity vector computed from the current position and velocity β 0 is a perfect circle, values approaching 1 are increasingly stretched ellipses, and 1 or above means the craft has enough energy to never return.
Q: Why use a symplectic integrator instead of simple Euler or RK4?
A: Plain Euler integration leaks energy every step, so a "stable" orbit slowly spirals outward or inward even though nothing is supposed to change. The semi-implicit (symplectic) Euler scheme used here conserves the orbit's shape far better over long runs at a fixed time step.
Q: Can I make the spacecraft escape the planet entirely?
A: Yes β raise the initial-speed slider above roughly 1.41Γ the circular velocity (the local escape velocity), or fire enough prograde burns, and the status readout switches to "Escape trajectory" with no periapsis-apoapsis pair.
Q: Why is the 3D version so different from this one?
A: The 3D page is a generic decorative template β spinning geometry groups with slider labels that don't drive any physics. This 2D page implements the real orbital-mechanics simulation that the title and description actually describe.