Patent GB-1488951-A (GB)
Title: Satellite momentum wheel
IPC: B64G1/28
Filed: 1975-02-02
Abstract: 1488951 Magnetically stabilized rotors SOC NATIONALE INDUSTRIELLE AEROSPATIALE 2 Jan 1975 [3 Jan 1974 10 Dec 1974] 86/75 Heading G1C [Also in Divisions G3 and H2] A magnetically suspended momentum wheel for satellites, comprises a rotor 1 enclosed in a stator 2, passive radial magnetic centering means at opposite ends of the rotor spin axis, active axial magnetic centering means slaved to an axial position sensor 209 and an axial velocity sensor 208, at least one damping means, at least one switchable motor generator, and a rotor spin shaft 3 having pivots 104, 104' which coact with abutments 4, 4' only in special circumstances e.g. during launch or failure of axial centering means. As described each passive radial centering means e.g. 200 comprises at least two coaxial magnetic cores 7, 8 on the rotor having axial magnetic fields in opposite directions, situated between opposed pairs of coaxial magnetic cores 9, 10 and 5, 6 on the stator. Each active axial centering means e.g. 206 comprises, on the rotor 1, a toroidal magnet having a radial field in which, on the stator 2 is situated a toroidal winding 65 which receives the correction signals from the axial velocity and position sensors 208, 209. The damping means for damping oscillations of the rotor 1, comprises firstly, the magnetic cores of the centering devices and, secondly, a conducting disc 61 on the stator and toroidal magnets 49-52 on the rotor 1. As described, the axial velocity sensor 208 comprises a magnetic core 71, on the rotor, which has a radial field relative to circular stator windings 70, the signal generated by movement of the core 71 relative to the windings 70 being transmitted to a monitor for delivering to the axial centering means. The axial position sensor 209 includes, on the rotor, a magnetic core 72 with an even number of alternating radial fields facing, on the stator three sets of axial loops, two sets being axially aligned and spaced, each set receiving more or less of the field depending upon the axial position of the core 72, a current being induced thereby dependent upon the axial position thereof, the third set lying so as to continuously experience the field, thereby producing a reference signal which allows a signal, after processing, to be produced which is independent of the rotor speed. In further embodiments, the axial control is effected by a single actuator being a one coil Fig. 10 (not shown) or two coil, Fig. 11 (not shown) actuator, the magnetic field generated thereby being superimposed upon a magnet field generated by magnets. Suitable operation of coil currents in one direction or the other allows axial forces in the air-gaps to be obtained proportional to the destabilizing errors ascertained by the axial velocity and position sensors 208, 209.  Motor generators 202, 203, Figs. 2 and 3, each comprises two rectangular sectioned cores 21, 22 and 23, 24 respectively on the stator 2 each supporting four toroidal windings 29-32 and 33- 36 respectively, and a toroidal field magnet element 25 or 26, made of samarium-cobalt, on the rotor 1. The element 25, 26 has a magnetic flux alternating over 180 degrees and directed circularly and closing back upon itself by reason of alternating polarities. Switching is effected to change the direction of the current from box 37 crossing the conductors in the air-gaps, and the energizing coils. Rotation continues at a speed determined by a switching clock slaved to sensor 43. The system also functions as a generator, the sensor 43 then controlling the current generated by the windings selected to obtain a uni-directional current.