Thermal vacuum qualification tests on a Teldix double-gimballed momentum wheel

A double-gimballed momentum wheel (development test model) was subject to thermal vacuum qualification tests. The procedure was completed satisfactorily and included functional checks, isothermal and temperature gradient exposure under vacuum. The anticipated diurnal oscillation period of the gimbals was accelerated by imposing a square cone motion on the wheel, of period about 7.5 mins. Thus about 3000 cycles were reached, representing many years' life in the satellite. The torques required to start slow gimbal motion, about roll and yaw axes, were measured at a number of points in the tests and showed no significant trends with time or dependence upon temperature level. Although the wheel operated stably, the bearing temperature rose to what are deemed excessive levels during isothermal operation at 55 C ambient.