Orbital simulation · runs in the browser

Design the rocket.
Write the code
that flies it.

Vivapse simulates spaceflight the hard way — six degrees of freedom, the real shape of the Earth, live weather over the launch site you picked, and real transfer windows to the Moon and Mars. You write the flight program. Physics decides whether you land.

Open the playgroundHow it works
Parking orbitr 15,178 kmv 5.125 km/sΔv +1.090 km/s

Recorded in the playground

From the workbench to the Moon.

Every frame comes off the simulator running in a browser — the interface, the flight and the landing are the real thing. Only the dissolves between shots were added. Pick a step to jump to it.

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Design the vehicle

Pick a preset or build your own: stages, engines, propellant. The delta-v budget and the checks answer as you change it.

Aster · 535.5 t · Δv 11.11 km/s

A tour of the playground

The flight program

The rocket doesn't fly itself.

Your program runs fifty times per simulated second. It reads the vehicle — altitude, velocity, attitude, dynamic pressure, propellant remaining — and commands throttle, steering and staging. Plain JavaScript, edited in the browser, with no autopilot underneath to catch you.

starter.js

1let phase = 'launch';23function update(fc) {4  switch (phase) {5    case 'launch':6      fc.throttle(1);7      fc.steer(90);        // nose straight up8      fc.ignite();         // clamps release once thrust > weight9      phase = 'ascent';10      break;1112    case 'ascent':13      // Pitch over once moving, then follow the velocity14      // vector — that is the whole gravity turn.15      if (fc.surfaceSpeed > 100)16        fc.steer(Math.min(85, fc.prograde), 0);1718      if (fc.propellant < 0.02) {19        fc.shutdown();20        fc.separate();21        fc.setPlane('orbit');22        phase = 'insertion';23      }24      break;25  }26}

What it produces

50100150255075KMDOWNRANGE · KMMECOBOOSTBACKAPOGEEENTRY BURNLANDING BURN

Orange is thrust. Everything between the burns is the vehicle falling, and the simulator is not helping it.

How flight programs work

Fidelity

Not a game engine.

Every number resolves to a named model, and the places where the simulation departs from reality are written down rather than hidden. Three physics audits say where those are.

Gravity

WGS84 + J2

An oblate Earth, not a sphere. Oblateness precesses your orbit the way it really does.

Vehicle

6-DOF rigid body

Three axes of translation and three of rotation, with per-stage engine groups and cold-gas thrusters.

Atmosphere

Live Open-Meteo

Real winds over your chosen launch site on the day, with Dryden turbulence layered on top.

Ephemerides

VSOP87D · ELP2000

Planet and Moon positions generated from IMCCE series, so a window is a real window.

Transfers

Izzo Lambert

The same boundary-value solver used to plan actual interplanetary trajectories.

Integrator

RK4 · 50 Hz

Fixed steps in flight; on cruise, steps sized by how fast the path turns — centimetres from an adaptive reference over a 280-day Mars transfer.

Verification

940 tests passing

Plus reference flight programs scored across launch sites and random weather seeds.

Honesty

Deviations documented

Three physics audits, with every place the model departs from reality written down.

Where the model stops being faithful

Destinations

Three worlds, real windows.

Launch windows are computed from where the planets actually are, not from a table of convenient numbers. Miss the Mars window and the next one is about twenty-six months out.

Earth, captured from the simulator's own globe

Orbit and come back

Earth

Climb through the atmosphere, circularise, deploy, then bring the stage home — entry burn, landing burn, and a pad you have to hit.

Injection
9.4 km/s to orbit
Cruise
Minutes
Radius
6,371 km
Moon, captured from the simulator's own globe

Flyby, orbit or landing

Moon

A trans-lunar injection out of parking orbit, a coast the simulator runs on rails, and a sphere-of-influence handover to lunar gravity.

Injection
3.1 km/s injection
Cruise
3–5 days
Radius
1,737 km
Mars, captured from the simulator's own globe

A real transfer window

Mars

Windows are computed from the real positions of both planets. Miss one and the next is roughly twenty-six months out.

Injection
3.6 km/s injection
Cruise
6–9 months
Radius
3,390 km

Courses

Learn the physics behind it.

Rocket engineering from the rocket equation to landing on Mars — written against a simulator that already implements all of it, so every lesson ends somewhere you can fly.

All courses

T+00:08:19 · Touchdown

Your turn to fly it.

The playground opens on a vehicle, a launch site and a program you can change. Nothing to install, nothing to sign up for.

Open the playgroundSource
VIVAPSEORBITAL SIMULATION

A browser orbital simulator. Imagery from NASA.