"A Hull Stabilizer reinforces the spaceship's frame, strengthening it and generally improving structural integrity. Multiple Stabilizers can work in unison to bolster the hull far beyond its normal limits. Sufficient hull stability is also needed for hyperspace jump capability."
The Hull Stabilizer requires a 3x3 space, of which 3x3 is solid. It requires a 1x1 passable operator tile along one specific side (presumably for maintenance).