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The sign accompanying the Descent Propulsion System mockup (actually, the DPS engine's sign is located on the Ascent Propulsion System (APS) mockup across the room). It reads

Descent Engine

For a successful manned lunar landing, the lunar module had to have a descent engine that could be restarted easily and could be controlled with a throttle. The astronauts needed the ability to fully control their descent and to hover over [the lunar surface].