🛰️ Orbital Transfer Lab

Interactive orbital mechanics you can actually fly — Hohmann transfers, gravity-assist slingshots, the Oberth effect, and replays of eight real missions, rendered in 3D and driven by real Kepler physics underneath, not canned animation.

→ Try it live — runs entirely in-browser, nothing to install.

What it does

Pick two planets, launch a transfer, and watch the actual Δv budget, transfer time, and phase angle play out — a real two-body Kepler solve runs underneath every animation. Four modes:

• Interplanetary transfer — planet-to-planet Hohmann transfers around the Sun, with launch-window timing (launch now or wait for next window)
• Earth orbit transfer — true-scale burns across the whole regime, ISS → GPS → GEO → graveyard orbit, plus a translunar injection out to the Moon at 384,400 km with its own launch windows and miss angle (1 unit = 1,000 km)
• Gravity assist — build a patched-conic slingshot and see the "free" Δv it steals from a planet's orbital motion
• Oberth effect — why burns are cheapest deep in a gravity well, visualized around any body from the Sun to a moon
• Historic missions — animated replays of Voyager 1 & 2, Galileo, Cassini–Huygens, New Horizons, MESSENGER, Juno, and Parker Solar Probe, pinned to real flyby dates with J2000 planet positions

Burn vectors are drawn where the engine actually lights, pointing prograde or retrograde with arrow length proportional to Δv, and change colour as each impulse goes from upcoming to spent.

Honest about scale. A live ruler in the corner reads the distance the camera is actually looking at, derived by inverting the active radial scale — so it stays correct under the square-root compression that brings Neptune on screen. Planets have to be drawn far larger than life to be visible at all, so the size exaggeration is stated outright (bodies ×1,193) and can be switched to Proportional (one multiplier, so Jupiter really is 11× Earth) or True (bodies on the distance scale, where they nearly vanish — which is the point).

Major moons (Galilean moons, Titan, Enceladus, the Moon, Titania, Triton) orbit at their real periods. Camera drags to orbit, scrolls to zoom, and can lock onto any body as it moves.

Run it locally

pnpm install
pnpm dev        # dev server
pnpm test       # 61 physics unit tests (vitest)
pnpm build      # production build

The physics — analytic two-body Kepler mechanics, pure TypeScript

All in src/physics/, no React/Three imports:

• vis-viva, circular velocities, periods, mean motions, Kepler-equation Newton solver (kepler.ts)
• Hohmann Δv₁/Δv₂, signed prograde/retrograde burn descriptors, transfer time, transfer-ellipse geometry, synodic period, departure phase angle, launch-window timing (hohmann.ts)
• general 2D conics from state vectors via the eccentricity vector — ellipses and hyperbolae alike (conic.ts)
• patched-conic gravity assists: planet-frame velocity rotation by the hyperbolic turn angle (flyby.ts)
• Oberth-effect energy accounting for an impulsive prograde burn anywhere on an orbit (oberth.ts)
• the spacecraft moves along the transfer ellipse at physically correct non-uniform speed via a Newton solve of Kepler's equation

All orbits are treated as circular and coplanar. 61 unit tests pin the numbers to textbook values (LEO 300 km → GEO ≈ 3.89 km/s total; LEO → lunar distance ≈ 3.11 km/s TLI, ≈ 5 d coast, Moon leading by ≈ 114°; Earth → Mars ≈ 5.59 km/s, ≈ 259 d, 44.3° phase, ≈ 780 d synodic).

The lunar transfer stays two-body on purpose — the Moon's own gravity is not patched in, so Δv₂ is the burn to circularize at lunar distance rather than a real lunar-orbit insertion. The telemetry panel says so.

Graphics

• Post-processing bloom + vignette (@react-three/postprocessing), toggleable
• Real NASA-derived maps for Earth (Blue Marble) and the Moon; seeded procedural textures for everything else — banded gas giants, rocky worlds, Saturn's rings with the Cassini gap
• Layered additive glow sprites for the Sun and planet halos, atmosphere shell on Earth
• Spacecraft model with engine glow and a fading motion trail
• Two parallax starfield layers

Architecture

src/
  physics/   pure Kepler/Hohmann/conic/flyby/Oberth math + vitest suites (km, s, rad, km/s)
  data/      historic mission waypoints (real dates + J2000 planet longitudes)
  state/     zustand store (config, sim clock, transfer state machine) + memoized selectors
  scene/     react-three-fiber scenes; km -> scene-unit mapping lives only in scale.ts
  ui/        Mantine control panel, telemetry readout, time bar, flyby inset diagram

Scene coordinates stay O(1–100) — never raw km in float32 buffers. Every path (transfer arcs, conics, mission trajectories) is point-sampled in physical space and mapped through the radial scale, so curves stay tangent to orbit rings even under nonlinear compression. Per-frame motion reads the clock transiently inside useFrame — React re-renders only on configuration changes.