The Spire Dock has a pair of Retractable doors that allow access to a cargo bay within the Spire, in which one can store massive objects. The doors are located at the Spire's top, and open automatically when something is being lowered into the Spire.
The doors have two wishbone-shaped clamps on each side, which are the first to retract when the doors are opening. The doors themselves open by curling outward in three long sections, forming a shape similar to a Mesoamerican pyramid when fully opened. Each section has a large green light on both sides, and at the center of its base, an ornate sun design. These doors can be scanned, but only from afar and not when on the Spire itself.
After assembling the Theronian Bomb, Samus is asked by Aurora Unit 217 to return to the Spire. Once there, she commands her Gunship to deposit the Bomb into the Spire for transportation to the Elysia Seed. The doors close once the Bomb has been placed, and are lost when the bomb-carrying Spire collides with the Elysia Seed's Shield.
"Retractable doors are closed and covering a large cargo bay capable of storing massive objects."