RESUMO
This paper describes the optical design of the visible telescope (VT), which is the primary payload for the Chinese-French Space-based multi-band astronomical Variable Objects Monitor (SVOM) mission, for the detection and observation of high-redshift gamma-ray bursts. The VT aims at reaching a limiting magnitude of +22.5Mv with the exposure time of 300 s in the 630 km Sun-synchronous orbit with an inclination of 30°. The VT, also known as the fine guidance sensor for the SVOM, aims to measure the relative performance error (RPE) of the platform during the tracking and provide the RPE to the platform to correct its stability. The optical design is presented in this paper. The mirror manufacture and test results are presented. The optical system performance, tolerance budget, thermal analysis, and stray light design of VT are fully analyzed. Finally, the diffraction encircled energy and point source transmittance are tested in the lab for the finished telescope.
RESUMO
The space camera with variable focal length is capable of capturing images with variable resolution and variable field of view. This is useful for space-borne reconnaissance because the camera can switch between coarse and fine reconnaissance flexibly. However, the traditional optical zooming relies on moving elements which might influence the momentum balance of the satellite platform. Therefore, we present a prototype design using the piezo deformable mirror (PDM) to realize an all-reflective optical bifocal zooming system. By changing the curvature radius of the PDM, the focal length can be switched between 48 and 192 mm without moving elements involved. With the focal length experiencing 4× magnification, the system performance is still approaching diffraction-limited performance, and the maximum stroke of the PDM is also within its physical limits. Experiments demonstrate that the principle is correct and the design is successful.
