Modeling, measurement and simulation of the disturbance torque generated via solar array drive assembly

The disturbance torque generated via solar array drive assembly(SADA) can significantly degrade the key performance of satellite.The discussed SADA is composed of a two-phase hybrid stepping motor and a set of two-stage straight gear reducer. Firstly, the vibration equation of the two-phase hybrid stepping motor is established via simplifying and linearizing the electromagnetic torque.Secondly, based on the vibration equation established, the disturbance torque model of SADA is created via force analysis and force system simplification. Thirdly, for precisely ground measuring the disturbance torque aroused by SADA, a measurement system,including a strain micro-vibrations measurement platform(SMMP) and a set of gravity unloading device(GUD), is designed.Fourthly, the proposed disturbance torque model is validated by measuring and simulating the disturbance torque produced via SADA driving rigid load through GUD. The results indicate that, the proposed disturbance torque model holds the ability to describe the disturbance torque caused by SADA with high precision. Finally, the disturbance torque emitted by SADA driving a flexible load, designed to simulate solar array, is modeled and simulated via using fixed-interface mode synthesis method(FIMSM). All the conclusions drawn from this article do have a meaningful help for studying the disturbance torque produced by SADA driving solar array on orbit.

Corrosion Behavior of Rusted 550 MPa Grade Offshore Platform Steel

The corrosion behavior of a rusted 550 MPa grade offshore platform steel in Clcontaining environment was investigated.The results revealed that the corrosion process can be divided into initial stage in which corrosion rate increased with accumulation of corrosion products and later stage in which homogeneous and compact rust layer started to protect steel substrate out of corrosion mediums.On the contrary,structural analysis of rust layers by X-ray diffraction showed that α-FeOOH increased from 1.3% to 3.6% and the Fe3O4 increased from 1.0% to 1.5% while γ-FeOOH reduced slightly according to corrosion time increased from 30 cycles to 73 cycles.The results of electron probe microanalysis indicated that Cr concentrated mainly in the inner region of the rust,inner/outer interface especially,whereas Ni and Cu were uniformly distributed all over the rust after 73 corrosion cycles.According to electrochemical measurements,it was found that the corrosion rate of rusted steel reduced from 0.61 mm/a after 45 cycles to 0.34 mm/a after 85 cycles,44.3% reduction approximately,and Rrust values increased with increment of corrosion time.Therefore,formation of compact inner rust layer and enrichment of Cr are important to improve corrosion resistance of offshore platform steel.