A novel measurement technique for the alignment of satellite reflectors and feeds: From subsystem to spacecraft and up to final RF testing

Balancing spacecraft performance and design against manufacturing capability and configuration control requirements is a fundamental process for any s/c. The balancing process defines the degree of success of a spacecraft program and the mission as a whole. The effort and energy expended defining and refining these issues consumes significant resources from virtually every component of the organization. A key product of this organization is to realize a successful mission wherein the process starts with 3D CAD definition of Mechanical/Optical/RF axes of various components, subassemblies, and major assemblies (Fig 1). After finalization of the 3D CAD definition the same is sent for the fabrication. Once the fabrication is over the critical geometries and parameters of each component are measured using the different contact and non-contact methods before the same is assembled to the spacecraft main assembly. The measurement of the geometries of the subsystem and their relative orientation with respect to the spacecraft main assembly is a challenging task. The alignment of the subsystems with respect to the spacecraft main assembly includes the measurement of six transformation parameters and correcting the deviations between the theoretical CAD model and the measured assembly. The evolving technology of intelligent cameras with automated photogrammetric measurements & use of computational metrology has recently begun to play a prominent role in enhancing the productivity and meet the accuracy requirements. An attempt is made to use the Close range Photogrammetry system with digital intelligent camera and various optical metrology techniques for spacecraft applications right from the fabrication stages of components to the final spacecraft main assembly. This paper provides the details of a case study carried out by performing measurements on the antenna system right from fabrication level to the final integration to the spacecraft. The paper further encompasses - arious error sources during the whole process and provides a brief on recent advancements in the optical and digital metrology techniques as well as their advantages/limitations over the existing conventional metrology techniques used for any typical s/c.