Propulsion module
When fully loaded with propellant at the time of launch, the spacecraft weighed only 1,060-kilograms (2,342 pounds). Most of Surveyor's mass lies in the box-shaped module occupying the center portion of the spacecraft. In reality, this center module is made of two smaller rectangular modules stacked on top of each other. One of the two smaller modules, called the equipment module, holds all of the spacecraft's electronics and science instruments. The other, called the propulsion module, houses Surveyor's rocket engines and propellant tanks.
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(From NASA)