Project
A small toolkit of interactive orbital-mechanics tools that run entirely in the browser — each one animating a real, honestly-computed trajectory rather than a textbook cartoon.
orb3e is a set of single-purpose tools for the classic problems of orbital mechanics, each one interactive and each one showing the real trajectory rather than a schematic. Set the inputs, read what it costs, and press play to watch the vehicle fly it. Everything runs in the browser, with nothing to install and nothing to keep alive.
It grew out of Spiral, a tool for the one corner the impulsive-transfer calculators ignore — continuous low-thrust spirals. Once that existed, the rest of the standard problems wanted the same honest, animated treatment, so Spiral became the first of six.
Low-thrust electric-propulsion transfers — the many-looped spirals that Dawn and modern comsats actually fly, integrated honestly enough that a too-eager thruster visibly fails to circularize and escapes. Optional J2 oblateness and GTO-to-GEO.
Two- and three-burn transfers side by side, with an optional plane change split optimally across the burns — so you can watch bi-elliptic overtake Hohmann exactly when a large inclination change is in play.
Given two points and a time of flight, the transfer orbit that connects them — the workhorse behind interplanetary targeting, solved with universal variables and checked against the textbook.
The path a satellite traces over a rotating Earth, drawn on a world map — the familiar sinusoid that drifts westward each pass, its turning latitude set by the inclination.
Clohessy–Wiltshire relative motion in the target’s co-orbiting frame — the docking problem, where a radial nudge quietly becomes an along-track drift and the right kick closes the loop.
A launch where gravity alone pitches the rocket over, integrated step by step — the flight-path angle bending down from vertical as the vehicle trades altitude for horizontal speed.
Most orbital mechanics is taught with static diagrams that quietly lie — the two-burn arc a real electric transfer never flies, the plane change that looks free. These tools take the opposite bet: compute the real trajectory, animate it on Kepler time so the vehicle slows where it’s supposed to, and let the honest behavior teach the lesson. Watching a vehicle crawl at a far apogee is a better argument for doing plane changes high and slow than any equation.
Every tool plays. Press the button and the vehicle flies the route while a trail fills in behind it; scrub to any moment and read the state.
A multi-page TypeScript build sharing one core: the propagators (a numerical integrator for Spiral, universal-variable Kepler and Lambert for the rest), a set of physics modules under a unit-test suite, and a common 3D-projection and playback layer. It’s served as static files from CloudFront — no server to keep alive. The continuous-thrust core in Spiral is the most involved piece; the rest are first-cut but real, with the honest numerics left in and the polish still to come.
It’s live and free at orb3e.erikevenson.net — six tools, all animated, nothing to install. Start with Spiral if you want the deepest one.