the disc 61 and spaced from the disc by a narrow axial air gap of approximately 0 010 34 an electrical coil is wound around each core and is operable when energized to interact with the disc to produce magnetic flux tending to attract the disc axially toward the respective electromagnet the coils are adapted to be energized by current supplied by the shaft controller 50 a non contacting position sensor 65 shown schematically in fig1 also is associated with the thrust controller detects the actual axial position of the shaft 16 and transmits a signal representative of that position to the controller the axially spaced electromagnets 63 of the thrust bearing 60 exert axially opposing magnetic forces on the disc 61 to hold the shaft 16 in a predetermined axial position if the shaft deviates from that position the controller 50 responds to the signal from the sensor 65 and adjusts the current supplied to the electromagnets 63 on either or both sides of the disc in order to return the shaft to its proper axial position in some air cycle machines an additional disc 67 fig2 and 4 is fixed to and projects radially from the shaft 16 adjacent the disc 61 and coacts with an annular and axially facing permanent magnet 69 fixed to the housing 15 the permanent magnet 69 is located at the side of the disc 67 adjacent the compressor 17 and exerts a constant force biasing the shaft axially toward the compressor in order to offset the axial force created as a result of the pressure differentials from the compressor to the turbine 18 the permanent magnet reduces the power required by the electromagnets 63 during rotation of the shaft backup mechanical bearings are provided in order to support.