Development of a bapta mechanism for small satellites

摘要

This work intends to show soem aspects about the mechanical layout and modeling of a BAPTA (Bearing and Power Transfer Assembly) mechanism in development involving a government institution (INPE) and private companies. The design here described is being evolved for application in small satellites (-0.5 kW with a rigid solar panel of approx 1.0 kgm~2). The selected concept uses a conventional 1.8~0 stepper motor and a 100:1 harmonic drive reduction gearing to achieve a theoretical output step size of 0.018~0. Simulations in computer are showing that significant interaction between the solar array and spacecraft can be avoided (spacecraft pitch disturbing velocity is on order of 10~-5 deg/sec) with power consumption as low as 5 W. The adequate determination of the power consumption is possible due to an adequate representation of the magnetic non-linearity in the motor, including its effect on the electromagnetic torque production. The reliable prediction of the important dynamic characteristics of the motor and general system necessitates a precise representation of the flux-linkage data. A good example is the single-step damping, which can be predicted satisfactorily only if the current disturbance and associated power loss in each stator circuit are calculated correctly. This requires that the rate of change of flux-linkage be defined accurately for any combination of the system variables.