ORRERY

What is this?

Orrery is a browser-based solar system explorer, mission simulator, and encyclopedia. Real orbital mechanics under the hood — Keplerian two-body propagation, Lambert solvers for transfer trajectories, the same equations real flight teams use. No backend. No accounts. Runs offline once it's loaded.

It's not a flight planner. There's no API to NORAD, no real-time TLE updates, no live launch-window predictions. The numbers are physically correct but stylised; the missions in the catalogue are real but their flight arcs are teaching models, not propagated state vectors.

Designed for everyone — curious lay people, students, space enthusiasts, mission planners who want a sandbox. Built for the browser so it works on any device with a screen. Open source under MIT. The catalogue covers 36 real missions across the inner solar system plus the Moon and four outer-planet destinations, and a fleet inventory of the spacecraft that flew them.

Why this exists

The project started during the lead-up to Artemis II. NASA was about to send four humans around the Moon for the first time since 1972, and the public conversation around it was almost entirely uninformed. People didn't know what 'free-return trajectory' meant. They didn't know why Mars launch windows happen every 26 months. They didn't know the rocket equation.

Orrery is the answer to that. Spaceflight is built on physics that's been understood since Newton. Most of what looks magical is actually visible — you can see the orbits, you can compute the transfer arcs, you can read every formula. The simulator is the front door; the encyclopedia is the textbook; together they're the project.

How to use it

Start at /explore. Spin the solar system. Click any planet to read its orbital elements — semi-major axis, eccentricity, true anomaly. The numbers are live.

Find a mission you care about in /missions — Curiosity, Apollo 11, anything from Sputnik onward. Read its FLIGHT tab to see the actual ∆v budget broken down across the five phases of every spaceflight: launch, trans-X injection, cruise, orbit insertion, EDL.

When something doesn't make sense — when a number on the HUD or a label on a chart confuses you — every term is linked to /science. The encyclopedia is meant to be read in order or hopped through depending on what you need.

/plan and /fly are the deeper end. /plan computes porkchop diagrams for any destination — pick a launch year, see when the windows open. /fly takes a mission and walks you through its trajectory phase by phase. The HUD shows everything in real units.