Inertia

Excess inertia will cause your ship to fall apart when damaged. To counteract this, you need to have more integrity on your ship than inertia. Larger ships have more inertia, thus requiring more structure. It is good practice to make sure you have extra structure, as it can get damaged in battle and cause your integrity value to dip below your inertia.

When integrity is below inertia, spooky groaning sounds will be heard, and upon the slightest amount of damage, the ship will start turning into swiss cheese, with holes popping up everywhere randomly.

The default tile for empty tiles on the ship is a basic structure tile with 300 points of integrity, placing any modules will replace these tiles, that includes structural modules.

Larger pieces of structure are more efficient at providing integrity per square occupied, so it's sometimes a good idea to place large pieces of structure early in ship building, rather than trying to wedge in small pieces later.