Rendezvous and docking
Two of your ships in the same orbit can be brought together and joined into one. Getting there is orbital mechanics; the last hundred metres is station-keeping; the joint itself is four conditions the latches will or will not accept.
Marking a target
Any ship of yours already in the world can be made the target of the one you are flying. On the flight's map, tap that ship to bring up its card, and the card carries a TARGET button. Once it is picked the button reads UNTARGET, and your own card grows three rows about it: RANGE, the gap right now; REL SPEED, how fast the two of you are moving apart or together; and CLOSEST, the nearest your path comes to it and how fast you will be going past when it happens.
Targeting is a flight thing. The button is only on the card while you are flying, because a target is something a ship is steered towards.
Where you will pass it
Marking a target puts closest-approach markers on your forecast, drawn in the same lavender the target is. They cover one lap of your orbit and no further: the nearest is titled CLOSEST and the one after it 2ND PASS. If the gap only ever closes over that lap, there is no nearest point in it to mark, and the single marker at the end of the lap is titled IN 1 ORBIT instead. As you fly past one, the search rolls on to the next lap, so the markers keep moving ahead of you.
Those markers are ordinary map markers. Tap one and the callout gives the distance, the time and the relative speed; you can set a reminder on it like any other.
A planned maneuver node is searched the same way, so the passes redraw as you drag the node's handles. That is how a rendezvous is actually set up: plan a burn, watch the CLOSEST figure fall, and stop when it is a few kilometres. See The map and maneuver nodes.
The navball in TARGET mode
While a target is set, the navball marks where it lies with a lavender ◉ in every mode, and puts a hollow mark directly opposite it. Point at the ◉ and burn and you close the gap; point at its opposite and burn and you open it.
Tapping the ball cycles the speed it reads: ORBIT, then SURFACE, then TARGET. In TARGET mode every speed on the instrument is measured against the target rather than the planet, the ⊙ and ⊗ marks become the direction you are drifting towards it and away from it, and the line under the ball reads RANGE. Burning at ⊗ in that mode is what kills the relative speed, which is the whole of a rendezvous: get the range small, then get the relative speed to nothing.
The last twenty kilometres
Inside 20 km the map stops being the instrument and a chip appears at the top left of the flight screen. It names the target, gives the range, gives the relative speed, and says in words whether the gap is CLOSING, OPENING or HOLDING. An arrow on the chip points where the target is on screen, and it turns as you steer. The chip turns from cyan to amber once the target is close enough to be drawn in the world beside you.
Your other ships are really there
Within a few kilometres, every ship of yours in this part of space is brought into the flight properly. It is drawn where it is, its own parts keep working, and it is solid. You can nudge it, and you can ram it, with the same consequences as any other collision: both ships take the blow and the parts under it are judged on the load. Only your own ships are brought in, and ones sitting on the ground are left alone.
What makes the latches catch
Docking needs a Docking Port on each ship, and nothing else will do: a port's face takes another port and no other part. When two ports meet, the latches close on their own if all four of these hold at once.
| Condition | The Docking Port's limit |
|---|---|
| Close enough | 0.6 m |
| Slow enough | 0.5 m/s |
| Square enough | 30 ° |
| Not turning against each other | 0.15 rad/s |
The two faces have to be pointing into each other, not merely near each other, and the ships have to be turning together rather than against each other. Where the two ports differ, the tighter of the two figures is what the joint is held to. The latches do not catch while time is warped, so fly the last stretch at normal speed.
When they catch, the flight says "Docked with" and the other ship's name, and there is one ship where there were two. Its parts are yours now, its tanks appear in your resource list, its thrusters answer your controls, and its card is gone from the map. Fuel and hypergolic propellant both cross the joint, which is what makes a tanker useful: dock one to a ship in orbit and its propellant is simply part of the ship.
Coming apart again
A joint you made can be undone. The Docking Port's own sheet offers Undock, and a stage can be set to do the same. Either way the joint is cut and the two halves are pushed gently apart. The half you are not flying carries on as a piece of its own and goes back into the world as its own ship once it is coasting. See Debris and dropped stages.
Two ports can also be joined in the hangar. That is how you build a ship with a joint it is meant to shed: a lander bolted to a transfer stage, undocked when it is time to go down.