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About this tool
Interactive N-body orbital mechanics simulator with velocity vectors, orbital eccentricity, escape velocity, and collision mechanics.
The Gravity Orbit Simulator integrates Newton's inverse-square law, a = −GM·r/r³, step by step to draw the path a small body takes around a fixed central star, and classifies the result as circular, elliptical, escape or decaying crash. You set the star's mass, the starting radius and the initial tangential speed, and the panel shows live distance and speed against the escape velocity √(2GM/r) for that radius. It is a teaching tool for anyone trying to see why a satellite that is too slow spirals in and one that is too fast never comes back.
Open Gravity Orbit Simulator on AltFTool — it loads instantly in your browser.
Drag "Central Star Mass" between 1000 and 15000, "Initial Radius" between 60 and 240 and "Initial Speed" between 1 and 15, or click an Orbit Preset: Circular Orbit, Elliptical Orbit, Escape Velocity or Spiral Crash.
The canvas relaunches on every change and integrates the inverse-square pull step by step, drawing the trail and a velocity-vector arrow; "Pause Orbit" freezes it and Reset relaunches from the current sliders.
The telemetry heading reads "Stable Circular Orbit", "Elliptical Orbit", "Hyperbolic Escape" or "Collision (Crashed)", beside the v_esc figure and the live Current Speed and Distance readouts.
Circular, elliptical, escape trajectory and decaying crash are classified live from the current speed against the circular and escape thresholds, not just drawn.
Buttons set the launch speed to the exact circular value, 75% of it for a bound ellipse, 110% of escape velocity, or 25% for a guaranteed crash — so each regime is one click away.
Current radius and speed update continuously next to the escape-velocity figure for your chosen mass and radius, making the energy trade-off visible.
v = √(GM/r), where M is the central mass and r the orbital radius. The simulator computes this for your slider settings and its circular preset applies it exactly; any deviation from that value turns the path into an ellipse.
Escape velocity is √(2GM/r), which is exactly √2 — about 1.414 — times the circular orbital velocity at the same radius. Below it the orbit is bound and closed; at or above it the body follows an open parabolic or hyperbolic path and never returns.
Because the tangential speed is too low for the radius, so the ellipse's closest approach falls inside the star's surface. The crash preset uses 25% of circular speed to show this deliberately; the run stops when the body reaches the star's radius.
No — the simulation uses scaled units with G set to 1, star masses from 1,000 to 15,000 and radii from 60 to 240, advancing time in fixed steps. The proportions and the physics are faithful, but the numbers are not kilometres and kilograms, so use it to understand the relationships rather than to plan a real transfer.