Bunker Door

The Bunker Door is a heavy defensive building used to seal off spaces from meteors and other hazards. It is especially useful on the surface and in rocket infrastructure, where its ability to support buildings lets it hold structures above it, including stacked rocket platforms or even stacked rockets, without blocking their use. Because of that, Bunker Doors are commonly used to build compact vertical launch setups.

A Bunker Door does not change its functional state until its opening or closing animation finishes. While it is still animating shut, it can continue to let meteors and light pass through, so timing matters in meteor protection builds. In the same way, a door that has begun to open is not instantly clear; its edges still do not block rockets only once it is fully open. This makes it possible to place two open doors next to each other to create an 8-tile-wide passage.

Bunker Doors share some behavior with Mechanized Airlocks. They can be controlled by automation, and their delayed physical state change means they are often used in precise timed systems. For reliable triggering, a green signal must last at least 0.4 seconds to open the door and a red signal must last at least 0.6 seconds to close it. The fastest stable oscillation wavelength is 1.4 seconds, and critical designs benefit from a little extra margin. In practice, this makes Bunker Doors suitable for automated meteor locks and other timed barriers, but less suitable for very rapid toggling.

A few practical points are worth keeping in mind:

• Bunker Doors can support buildings, making vertical rocket stacks possible.
• A closing door is still vulnerable until the animation completes, so a partially closed door does not yet count as sealed against meteors.
• If a door is closed partway through an animation and the game is saved and reloaded, the animation state is not preserved; it will restart and take another full opening or closing cycle.
• The door can be submerged and still operate, although its speed while submerged is the same as when it is unpowered.

Bunker Doors can also be used in automation builds that rely on a red-green-red pattern to force a door into a locked, protective state before the animation visually completes. This is useful when the goal is to protect a base from meteor damage as quickly as possible. In high-traffic corridors, however, they are less about convenience and more about durability and environmental sealing than the faster everyday access provided by other airlock types.