Balloon-Borne VLBI Reflector Structural Design Considering Failure of Sub-Reflector Adjustment Mechanism Using Multiobjective Optimization

Abstract

The balloon-borne VLBI (very long baseline interferometry) is a radio telescope for space observation from the stratosphere in the submillimeter wave band. The primary reflector has an aperture of 3 m in diameter whose degradation of aperture efficiency is required to be less than 17 % under the deformation due to variations of elevation angle and temperature during observation. In order to alleviate the deterioration of the aperture efficiency, the sub-reflector is equipped with a focal position adjustment mechanism. However, the adjustment mechanism may fail during observation, so that the focal position will be fixed at the prescribed position. This study evaluates the effect of the adjustment mechanism failure on the aperture efficiency through multiobjective optimization approach. The design problem has thirteen objective functions that correspond to the nominal observation condition and the other six conditions considering elevation angles and temperatures with normal and failure cases of the adjustment mechanism. The design problem is solved using the satisficing trade-off method (STOM). As STOM can obtain the single Pareto solution corresponding to the user's preference for each objective function by introducing an aspiration level, the trade-off analysis is easily performed.