AAS 204th Meeting, June 2004
Session 81 Herschel FIR/Sub-mm Astronomy Mission
Special Session Related Poster, Thursday, June 3, 2004, 9:20am-4:00pm, Ballroom

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[81.05] Cryogenic Far-IR Laser Absorptivity Measurements of the Herschel Space Observatory Telescope Mirror Coatings

J. Fischer (NRL), T.O. Klaassen, J.N. Hovenier (TU Delft), G. Jakob, A. Poglitsch (MPE), O. Sternberg (NRL)

Far-infrared laser calorimetry was used to measure the absorptivity, and thus the emissivity, of aluminum-coated silicon carbide mirror samples produced during the coating qualification run of the Herschel Space Observatory telescope to be launched by the European Space Agency in 2007. The samples were measured at 77 Kelvin to simulate the operating temperature of the telescope in its planned orbit around the second Lagrangian point, L2, of the Earth-Sun system. Together, the telescope equilibrium temperature in space and the emissivity of the mirror surfaces will determine the far-infrared/submillimeter background and thus the sensitivity of two of the three astronomical instruments aboard the Observatory, if stray light levels can be kept low relative to the mirror emission. Absorptivities of both clean and dust-contaminated samples were measured at 70, 118, 184 and 496 \mum. Theoretical fits to the data predict absorptivities in the range 0.2 -- 0.4% for the clean sample and 0.2 -- 0.8% for the dusty sample, over the spectral range of the Herschel Space Observatory instruments.

This work was funded by the ESA Herschel/Planck Project Office, the Office of Naval Research, and the NASA Herschel/Planck Project Office at JPL.

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