Placed on the Sun-Earth L2 Lagrange point, SPICA will operate in the 5 to 210 μm wavelength range. Astrium has been contracted by ESA/ JAXA to update the study of the SPICA telescope from a 3.5 m design (compatible to the Japanese HIIB launcher) to a 3.2 m design (compatible to the HII-A with the short 5S fairing): despite a similar fairing diameter, the shorter length of the fairing envelope results in a reduction of the M1-M2 distance and an associated diameter reduction of M1. Maximization of the M1-M2 distance within the constraints is important to maintain a reasonable polishing criteria of the main reflector. Therefore the M2 assembly sizing and the back focal length become main parameters for the telescope optical design. The main constraints are driven by the telescope requirements such as focal length, maximizing the diameter of M1 (3.2 m) and, M1 f-number (critical for the manufacturing aspects). The WFE must be below 350 nm rms, and operational temperature below 6K. . The main issues addressed in this paper are: - an improved telescope design based on the Astrium background in Silicon Carbide technology which has been tried-an-tested for mirrors and structural parts on several space projects, including HERSCHEL and Gaia (brazing, polishing, assembling, iso-static mountings). - performances which are taking advantage of the SiC properties ,such as homogeneity of the single-phase material inside the structure, and structural stability from ambient to the operational temperature range. Our study shows that the SiC telescope design can fulfil all the mechanical and optical requirements for SPICA. - the verification and optical tests definition which will be key elements in the qualification of the telescope to be incorporated in the logic of the satellite verification activity to be conducted in Japan.

Date Published: 13 September 2012
PDF: 13 pages
Proc. SPIE 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 84502P (13 September 2012); doi: 10.1117/12.926891

Published in SPIE Proceedings Vol. 8450:
Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II
Ramón Navarro; Colin R. Cunningham; Eric Prieto, Editor(s)