Scarab's rear compartment houses a removable payload bay immediately behind the drill cavity. The payload must fit entirely within the curved shell, and must be approximately 100kg (220lbs) to balance the rover.
When performing a science mission, a sensor suite is stored in this bay. After drilling, samples are dropped into the back of the rover for processing.
During mobility tests and long traverses the science payload is removed. The bay may instead be filled with weights, extra batteries or other equipment.