Fly the capsule, dock with the station

How to dock

Space Dock is a free space docking simulator you can play in your browser — no download and no account. You fly a crew capsule from its cockpit, 408 km above the Earth, and bring it into the forward docking port of a space station: the modules, the truss and the solar arrays ahead of you, the planet sliding by below at 7.66 km a second. Every docking is scored, and after each one the capsule refuels, undocks and starts again from further out — off-axis, turned, turning and drifting.

The controls

• Translation moves the capsule without turning it: forward and back (W, S), left and right (A, D), up and down (R, F) — or the left hand controller and the Forward and Back buttons.
• Rotation turns it: nose up and down (↑, ↓), yaw left and right (←, →), roll (Q, E) — or the right hand controller and the Roll buttons.
• Fine (T) cuts every thruster to a fifth, for the last few metres.
• Rate hold (H, on to start) makes the rotation controls set a turn rate and stop it when you let go. Switch it off and the capsule keeps turning until you push the other way — as it would with no computer helping.
• View (C, or the View button) switches between the cabin and an outside camera behind the capsule, where you can watch it — and its thrusters puffing — as it closes on the station. The displays stay under both.

The displays

• PROX OPS — range and closing rate to the port, the offsets and rates on each axis, and side and top views of the approach corridor with your track.
• ALIGNMENT — a docking scope: the circle is how far off-centre you are, the cross where the nose points, the tick at the top your roll. Roll, pitch and yaw errors and rates, and the RCS modes.
• SYSTEMS — propellant, which thrusters are firing, the orbit, the cabin air, the mission clock and the caution lights.

Docking

First line up: put the attitude cross in the middle of the scope, then centre the circle with left/right and up/down. Then close in — a few tenths of a metre a second while far out, under a tenth for the last ten metres — correcting as you go. The capture limits: less than 0.3 m off-centre, closing at no more than 0.3 m/s, nose and roll within 5°, almost no turning. A gentle miss bounces off the port; anything harder, or touching the station anywhere else, is a collision. Run out of propellant or drift more than 600 m away and the mission is over.

Orbital mechanics

Nothing here flies in a straight line for long. Near the station, motion follows the Clohessy–Wiltshire equations of a 408 km orbit: push towards the station and you slowly sink below its axis; sit above or below it and you drift along-track. The effect is gentle, but over a minute or two it adds up — watch the offsets and keep correcting, as real crews do.

Frequently asked questions

Is Space Dock free?

Yes. It is free to play with no sign-up, no download and no in-game purchases.

How realistic is it?

The capsule moves as a real one does near a space station — orbital relative motion, thrusters on six axes, rotation that keeps going without rate hold — and the capture limits are close to real ones. The station, the capsule and the displays are made up, not copies of any real spacecraft. It is a game, not a training device.