to back compressor pistons 2 and 4 in a compressor module 6 and a pair of expander and balancer pistons 8 and 10 in an expander module 12 the cryocooler and the adaptive feedforward vibration control system can be mounted on board a spacecraft which is indicated generally by block 14 a control system 16 for the compressor module 6 can be identical in structure to a control system 18 for the expander module 12 and therefore the vibration control of the compressor module described below is also applicable to the expander module the control systems 16 18 for the compressor and expander modules 6 12 can share the same processor 20 for the compressor module 6 a vibrational force sensor 22 preferably a 34 load cell 34 is attached to a fixed location on a support mounting of the cryocooler other types of vibrational force sensors such as load washers and accelerometers can also be used the location of the force sensor is called a force measurement point each piston is equipped with a position sensor that measures the piston 39 s position in real time the piston 39 s drive force f can be derived from the equation equ1 where m is the piston mass x is the piston position and t is time a force injection point is where.