Photo: Randi Silberman
WARMING UP: On a sunny afternoon in Costa Rica, engineers at Ad Astra Rocket Co. prepare to test a heat shield for an electric rocket. It is the brainchild of Franklin R. Chang Díaz, a former NASA astronaut. Instead of combusting hydrogen and oxygen, as in a chemical rocket, this engine uses radio-frequency generators to heat a gas, turning it into a plasma. By blasting the plasma out a nozzle, the rocket generates thrust.











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