The JASPER (Joint Actinide Shock Physics Experimental Research) facility at the Department of Energy's Nevada Test Site is home to the two-stage gas gun, a 30-meter-long, two-stage device to strengthen scientists' ability to ensure that the nation's nuclear stockpile is safe and reliable. Scientists fire projectiles from the JASPER gas gun into plutonium targets equipped with instruments for measuring and recording data. The projectile's impact produces a shock wave that passes through the target in a millionth of a second or less, creating pressures of more than 600 gigapascals (6 million times the pressure of air at Earth's surface), temperatures to thousands of kelvins, and densities several times that of plutonium's original solid state. The JASPER team's role in the Stockpile Stewardship Program is to measure the fundamental properties of plutonium. Data from the experiments are used to determine material equations of state, which express the relationship between pressure, density, and temperature. The equation of state is essential for generating reliable computational models of plutonium's behavior under weapons-related conditions. Knowledge of these properties is required to assess, without nuclear testing, the performance, safety, and reliability of nuclear weapons.