 A human-crewed Orion, however, must use some sort of damping system behind the pusher plate to smooth the near instantaneous acceleration to a level that humans can comfortably withstand – typically about 2 to 4 "g".The high performance depends on the high exhaust velocity, in order to maximize the rocket's force for a given mass of propellant.The velocity of the plasma debris is proportional to the square root of the change in the temperature ("Tc") of the nuclear fireball.