Investigation of optical error budget for the DORA telescope*

The Deployable Optics for Remote Sensing Applications (DORA) is a space demonstrator realized to evaluate the performances of a Cassegrain telescope (aperture f/16, entrance pupil $\boldsymbol{\varnothing}\mathbf{300}\ \mathbf{mm}$ FOV 0.16°) mounted in a mechanical structure capable to extend in operative position after launch. This solution offers the advantage of a reduced volume allocation onboard small and minisatellites resulting in better exploitation of resources. The entire telescope breadboard has been assembled and it is undergoing alignment and optical tests measurements. Hereafter, we describe the optical alignment setup and outline the optical system error budget, which has been achieved by means of a twofold procedure: one consisting in fitting the profile maps of the manufactured mirrors with Zernike polynomials to estimate the aberrations; the other one importing directly the grid relative to the mirrors surface maps with increased resolution into the optical design software, in order to estimate the actual variation of the spot diagram through focus and the image quality.