A protection device for an optical instrument of a satellite including a body on which the optical instrument is mounted, the optical instrument including a central mirror and peripheral mirrors reflecting light towards the central mirror, said protection device having a folded position and a deployed position, includes a plurality of panels rigid in the deployed position, the device forming a cellular structure including a tube for each peripheral mirror, the section of the tubes being a polygon, the tubes being disposed in such a manner as to protect the peripheral mirrors against stray illumination, and said panels being held against the body of the satellite in the folded position.