Engines are mounted on massive test stands built to handle extreme heat, high-pressure exhaust, and volatile fuels. When fired, engineers measure thrust, fuel efficiency, combustion stability, and durability under real launch-like conditions. Different engines—liquid, solid, or hybrid—are tested in their own ways. For liquid engines, super-cold fuels like liquid hydrogen and oxygen are pumped in and ignited to produce controlled thrust. Hundreds of sensors monitor pressure, temperature, vibratio