IMAGE QUALITY-CONTROL AND ALIGNMENT OF A SUBMILLIMETER BALLOON-BORNE SEGMENTED TELESCOPE

PRONAOS is a balloon-borne system dedicated to astronomical observatio ns in the submillimeter range (180 mu m - 1050 mu m) based on the use of a 2m Cassegrain telescope. The primary mirror consists of six CFRP (Carbon Fiber Reinforced Plastic) panels, each being positioned by thr ee actuators, The rotation angles of the panels have been measured in the visible range with the help of a CCD and digital centroiding techn iques that were necessary because of the light scattering on the CFRP mirror. The translation movements (along the optical axis) of the pane ls have been measured with an interference technique in the submillime ter range, Both visible and submillimeter measurements were also neces sary to determine the alignment of the telescope - focal instrument sy stem with the star sensor. The whole alignment process leads to a prec ision of +/-8 '' for che rotation angles and +/-7 mu m for the transla tion of each panel, sufficient for a qualification of the system.