FORMOSAT-5 consists of a spacecraft bus and an electro-optical payload. The payload is an f/8 Cassegrain type telescope with 3.6-m effective focal length. The spacecraft has a ground sampling distance of 2-m for panchromatic and 4-m for multispectral bands, with a 24-km swath width. FORMOSAT-5 is the first space program that National Space Organization (NSPO) takes full responsibility for the complete satellite and payload system engineering. The optical system assembly (OSA) has been successfully aligned and is now undergoing final performance verification tests at system level. To help create this unique instrument, NSPO has developed the computer aided alignment method assisted with the mechanical ground support equipment to carry out the assembly, alignment, and verification of the complex systems. This method offers an integrated capability for interferometric alignment and characterization of the large instrument. A detail OSA integration and verification steps, including primary mirror, secondary mirror, corrector lens and baffles alignment are presented. This paper describes the overall capability of this method and uses decomposed Zernike polynomials from the alignment and characterization of the OSA to verify the reduction of the wavefront errors and misalignments. It further demonstrates the successful completion of the instrument and satisfaction with the main system requirements.
Stray light analysis of FormoSat-5 telescope has been studied. The geometric contour profiles of the baffles are
determined by checking the degree of blocked direct-incidence stray light. Trade-off between different baffle contours
has been made by comparing the direct-incidence stray light, incident energy ratio, and incident energy uniformity of the
focal plane assembly (FPA). Detail studies have then performed on the contribution of the stray light due to direct
incidence, scattering from components, and multi-reflection between optical components. The effect of the FPA
structure is also considered since it is the component adjacent the most to the FPA. In addition, the tolerance of the
baffles fabrication and assembly are introduced.