Building a rocket

A rocket in the hangar is not a picture, it is a chain of parts joined at their points. Knowing how a join works tells you why a part snaps where it does, why a wing sits over a tank instead of beside it, and what the numbers along the top of the screen mean.

Three ways a part joins another

Every part carries named points where it can join. Drag one part near another and the game pulls it into place the moment a compatible point is close enough; let go and the two are connected.

Most points are stack points: a pod's bottom, a tank's top and bottom, an engine's top. They sit on the part's own axis and only join end to end, which is how a pod, a tank and an engine become a single line.

Radial points sit on a part's flank and face outward, the way the point on a Fin's inner edge does. They join a part to the side of whatever it is offered to, which is how fins and landing struts hang off a tank instead of stacking on it.

A fin selected on the starter rocket, its properties sheet open below with Rotate, Flip and Symmetry buttons and a Size slider. — A fin, joined by the point on its inner edge.

The Wing is different again: its one point has no direction, so it is a stud. A stud does not join to another point at all. It joins to a face, the whole flat side of a part like a tank's body. Drop a stud anywhere inside a face and it lands exactly where you let go, with no pull and no tilt. That is why a wing lies flat over a tank's picture instead of standing beside it: its span points out of the screen, toward you, not across it.

A wing lying over the fuel tank as a pale leaf shape, with the lift arrow pointing sideways from the centre of mass. — The wing over the tank. The green arrow is lift, and it points sideways because the wing's span faces the camera.

Studs and faces only ever pair with each other; two faces never join, and a stud never joins another stud.

Mirroring a part

A part selected on the canvas can be flipped where it stands, or mirrored onto the other side of whatever it hangs from with a linked twin that follows every change you make afterward. See Mirror a part for both.

Resizing a tank

A Fuel Tank is not a fixed size. Select it, open its properties sheet and drag the Length slider: the tank grows or shrinks from the middle, whatever is stacked on top or below rides along with it, and its mass, price and how much it holds all scale with the new length. See Resize a tank.

The properties sheet

Selecting a part opens its sheet at the bottom of the screen: its name, then three placement buttons: Rotate, Flip and Symmetry. Below them is a row for every property the part has, a slider or a switch you can change right there. A part with nothing to adjust says so instead of showing empty rows. Some rows only appear on this sheet in the hangar; others follow the part into flight, where a tap opens the same sheet.

Reading your ship

The strip along the top of the hangar always shows three figures: Mass, TWR and Cost. TWR is how hard the engines push against the ship's own weight. Above 1.0 it can lift off the ground. Tap the strip and it opens into a full breakdown: the number of parts, the dry mass with no fuel aboard, the height, the thrust and fuel a lit engine gives you, and the cost again. A warning takes over one of those lines in place of a figure: the ship is short of credits, too big for the launch pad, has a payload standing through a fairing that should be sheltering it, or is in several pieces that are not joined to each other at all.

On the canvas itself, four coloured arrows show the forces acting on the ship as it stands: a yellow arrow for weight, straight down from a checkered marker at the centre of mass; a pink one for thrust, from wherever the lit engines push; a blue one for drag, against the direction you are facing; and a green one for lift, from the centre of any wings or fins aboard. Nudging a part and watching where these arrows move and how long they get is the fastest way to see whether a ship will fly straight or tip on the way up.

The starter rocket with its tank lengthened, the readout showing higher mass and cost, and the weight, thrust, drag and lift arrows over the ship. — Mass, TWR and Cost along the top; weight, thrust, drag and lift on the ship itself.

The pad decides what can fly

None of this matters if the finished ship cannot leave the ground: the Launch Pad you are standing on caps how much a rocket may weigh and how tall it may stand, and a ship over either limit is refused when you try to fly. A higher-level pad raises both caps. See Buildings for what each level allows and The Space Center for upgrading one.