The method for aligning the focal plane assembly (FPA) with the optical structure assembly (OSA) involves finding a position with optimal focus. The experimental setup includes a collimator with an effective focal length of 10,500 mm and a free aperture of 700 mm. An electronic ground support equipment (EGSE) is responsible for capturing the sensor signals. Processing these data allows the derivation of the contrast transfer function (CTF) value using a line-pair pattern. At the beginning of the FPA alignment process, the attitude and position of the FPA are controlled with the assistance of a hexapod positioning system (a six-axis robot). After determining the attitude and the best focus position of the FPA, shimming is performed to adjust the gap between the FPA and the OSA. Based on the shim thickness required at three orientations, shim rings with the relevant thickness are installed. Due to the uncertainties from shimming, shim ring thickness manufacturing tolerance, and the residual of the tip/tilt angle between the FPA and the OSA during alignment, it is crucial to confirm and fine-tune the shim ring thickness. Once the FPA is fixed on the OSA, moving the FPA for the through-focus measurement is not feasible. However, the distance between the primary mirror and the secondary mirror of the collimator is tunable. By adjusting this distance, the collimation beam can be modified to a converging or diverging beam, thereby changing the focal plane position. Consequently, through-focus measurements can still be conducted by moving the secondary mirror of the collimator.
The interferometry is often adopted to check the optical quality and support the alignment in assembly for high precision demand optical system. The interferometer could acquire the system wavefront error (WFE) and obtain the delicate variation of aberration terms. For those optical systems applied to the space mission, the transition from atmosphere to vacuum environment would lead to the dimensional changes of mechanical structure within the scale of micrometer and eventually diminish optical performance. Consequently, as stated above, it is essential to validate the whole optical system in vacuum circumstance. Before the system actually being launched into the space, they are usually placed in the thermal vacuum chamber during ground testing in order to validate if the design could withstand the harsh environments such as high vacuum level and large temperature difference. Nevertheless, it is a big challenge to build up an in-situ optical measurement architecture for large aperture optical system in the thermal vacuum chamber due to the finite internal space of chamber, limited aperture size of transmission view port of chamber door and thermal dissipation problem of measuring instruments. In this paper, we demonstrate an innovative way of interferometry for monitoring the optical performance variation of FORMOSAT-8 (FS-8) optical system assembly (OSA) in our current vacuum chamber that the test telescope and the diverger lens were located in the vacuum environment, while the interferometer stayed in the ambient circumstance. The interferogram was successfully obtained thanks to the rigorous optical alignment process and the speical designed reference tools.
In the paper, we proposed a compact Korsch-type CubeSat telescope for optical remote sensing validation. The optical payload will be mounted on a 6U CubeSat named ONGLISAT. This telescope has an aperture of 92 mm and an effective focal length of 725 mm, providing a field of view of 2.2 degrees. The optical payload is equipped with a linear TDI CMOS image sensor, capable of capturing high-resolution panchromatic images with a ground sampling distance (GSD) of 2.8 meters in a low-Earth orbit at an altitude of 406 kilometers. The Korsch telescope consists of three aspheric mirrors (primary, secondary, and tertiary mirrors) as well as a roof mirror. This paper presents details of the optical design, assembly, integration, and performance test for the compact Korsch telescope. The image quality of the Korsch telescope is evaluated by the contrast transfer function (CTF). Finally, after thermal vacuum cycling testing and vibration testing, the telescope still maintains a CTF of 0.12 at 50 lp/mm line pairs. The Korsch telescope has the characteristics of a low obstruction ratio and high stray light blocking. The design of the telescope has higher resolution, a smaller size, and lower launch costs, which are beneficial for future applications in science, agriculture, commerce, and disaster relief. Furthermore, its optical quality can be quickly validated, serving as a preliminary study for larger telescopes.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.