spring rate to be controlled in real time to react to various undesired conditions in one example an undesired natural frequency may be detected and the controller 22 provides a command to the actuator 20 to provide a desired number of unsupported coils corresponding to a spring rate that negates the natural frequency of the first member 12 the sensor 24 provides feedback to as to the effectiveness of the adjustment made by the controller 22 in another example a user may simply actuate the switch 26 to select a desired spring rate by feel for example referring to fig3 4c one example application is a vehicle 36 such as a rocket the vehicle 36 includes first and second portions 112 114 that respectively correspond to a propulsion section and an occupant area the adjustable spring system 110 is arranged between the first and second portions 112 114 when an undesired natural frequency from the propulsion section exerts undesired loads on the occupant section the adjustable spring system 110 changes the spring rate between the first and second portions 112 114 to minimize the loads in the occupant area one example system 110 that may be used for the vehicle 36 is illustrated in fig4 a 4c multiple springs 116 of corresponding spring assemblies 111 are arranged between the first and second portions 112 114 to synchronize the spring assemblies 111 an epicyclic gear train 38 is used the epicyclic gear train 38 includes a sun gear 40 operatively coupled to the actuator 120 each spring assembly.