An Attitude Metrology Based on Gyro-Theodolite for the Optical Cube Reference on Spacecraft

Abstract

Optical cube is a common reference for the attitude determination of spacecraft equipment during assembly and integration. Three orthogonal normal directions to the reflective cube face can describe a reference coordinate system. Commonly, the cube attitude measurement often employs the use of theodolite autocollimation metrology. It requires that several theodolites be properly positioned in front of the cube to collimate the cube face and then to view each other’s collimated light. For some large and complex spacecraft, due to the layout of the instruments on the spacecraft, theodolites should be placed far away, sometimes the collimated light between theodolites may be blocked by other instruments or structure on spacecraft. We describe an alternative metrology for this demand. This metrology is based on gyro-theodolite which can provide a natural azimuth reference, so that theodolite bucking can be cancelled. This method was used to successfully measure the relationship information between in-cabin equipment and out-of-cabin equipment in the TianGong spaceship and has been used on other spacecraft projects. In this paper, the proposed metrology based on gyro-theodolites is compared with the conventional metrology based on theodolites in details, and the theory is discussed. Finally, a case application is given and the angular metrology results are analyzed.