Focal plane alignment and testing for an off-axis multispectral space borne camera

To meet the requirements of high alignment accuracy for a multispectral camera, a focal plane subassembly is designed. Meanwhile, the instruments, fixtures and methods for alignment and measurement are described. First of all, the focal plane subassembly is mounted to the optics so that deflections and shifts of the CCD photosensitive area related to the image plane could be measured and calculated. According to the results given previously, the removal dimension of adjustment spacers is determined and preliminary modification is applied to the spacers. Thereafter, the focal plane subassembly is remounted. Then, the CCD is fine adjusted to its correct orientation and location, and locating pins are embedded into the spacers to hold this adjustment. Finally, based on the fitted optimum focal plane position, spacers are carefully ground and restored. Thus, the alignment is completed. Test results show that, three-dimensional deflections are Δα=-6.7", Δβ=1.9' and Δγ=13.2" respectively; three-dimensional shifts are Δx=-0.004 mm, Δy=0.006 mm and Δz=-0.070 mm respectively. The Modulation Transfer Functions(MTF) corresponding to four spectra and whole field of view are more than 0.25, which can meet the design and alignment specifications. The measurement and calculation error analysis shows that the equipments and methods can meet the precision requirements and provide technique references for homologous cameras.