Focus adjustment method for CBERS 3 and 4 satellites Mux camera to be performed in air condition and its experimental verification for best performance in orbital vacuum condition

The first Brazilian remote sensing multispectral camera (MUX) is currently under development at Opto Eletronica S.A. It consists of a four-spectral-band sensor covering a 450nm to 890nm wavelength range. This camera will provide images within a 20m ground resolution at nadir. The MUX camera is part of the payload of the upcoming Sino-Brazilian satellites CBERS 3&4 (China-Brazil Earth Resource Satellite). The preliminary alignment between the optical system and the CCD sensor, which is located at the focal plane assembly, was obtained in air condition, clean room environment. A collimator was used for the performance evaluation of the camera. The preliminary performance evaluation of the optical channel was registered by compensating the collimator focus position due to changes in the test environment, as an air-to-vacuum environment transition leads to a defocus process in this camera. Therefore, it is necessary to confirm that the alignment of the camera must always be attained ensuring that its best performance is reached for an orbital vacuum condition. For this reason and as a further step on the development process, the MUX camera Qualification Model was tested and evaluated inside a thermo-vacuum chamber and submitted to an as-orbit vacuum environment. In this study, the influence of temperature fields was neglected. This paper reports on the performance evaluation and discusses the results for this camera when operating within those mentioned test conditions. The overall optical tests and results show that the "in air" adjustment method was suitable to be performed, as a critical activity, to guarantee the equipment according to its design requirements.