38 pushes against a valve spool 40 which pushes against a valve opening spring 42 in another embodiment a linear motor or electromechanical actuator may be used to displace the valve spool 40 in the shown example the axial force exerted by plunger 38 causes the valve spool 40 to shift to the left compressing the valve opening spring 42 and decreasing the mass flow rate of the propellant entering the turbine 22 through the turbine inlet port 30 as the turbine 22 spins faster more alternating current power is generated at the permanent magnet generator 32 creating more direct current power rectified by the passive rectifier 34 as direct current power in the valve control solenoid 36 increases the electromagnetic force applied to the valve control solenoid plunger 38 increases the increased electromagnetic force results in an increased axial force exerted by the plunger 38 the increased axial force exerted by the plunger 38 pushes the valve spool 40 which pushes the spring 42 to push the valve 28 further closed which decreases the mass flow rate of propellant entering the turbine 22 thus decreasing the speed of the turbine 22 when the turbine 22 reaches a desired speed the axial force generated by the valve control solenoid 36 is balanced with the spring force of spring 42 such that the valve 28 is open just far enough to maintain a desired speed of the turbine 22 as the speed of the turbine 22 decreases the electromagnetic force applied to the valve control.