Quality evaluation of spaceborne SiC mirrors (II): evaluation technology for mirror accuracy using actual measurement data of samples cut out from a mirror surface.

The authors studied the quality evaluation technology of a spaceborne large-scale lightweight mirror that was made of silicon carbide (SiC)-based material. To correlate the material property of a mirror body and the mirror accuracy, the authors evaluated the mirror surface deviation of a prototype mirror by inputting actually measured coefficient of thermal expansion (CTE) data into a finite element analysis model. The CTE data were obtained by thermodilatometry using a commercial grade thermal dilatometer for the samples cut from all over the mirror surface.

Quality evaluation of spaceborne SiC mirrors (I): analytical examination of the effects on mirror accuracy by variation in the thermal expansion property of the mirror surface.

The Japan Aerospace Exploration Agency has studied a large-scale lightweight mirror constructed of reaction-bonded silicon carbide-based material as a key technology in future astronomical and earth observation missions. The authors selected silicon carbide as the promising candidate due to excellent characteristics of specific stiffness and thermal stability. One of the most important technical issues for large-scale ceramic components is the uniformity of the material's property, depending on part and processing.

Cryogenic optical testing of an 800 mm lightweight C/SiC composite mirror mounted on a C/SiC optical bench.

We tested the optical performance at cryogenic temperatures of an 800 mm diameter lightweight mirror, consisting of carbon-fiber reinforced silicon carbide and with a mass of 11.2 kg. The ceramic composite of the mirror was HB-Cesic, developed by ECM, Germany, and Mitsubishi Electric Corporation, Japan.

Cryogenic optical measurements of 12-segment-bonded carbon-fiber-reinforced silicon carbide composite mirror with support mechanism.

A 720 mm diameter 12-segment-bonded carbon-fiber-reinforced silicon carbide (C/SiC) composite mirror has been fabricated and tested at cryogenic temperatures. Interferometric measurements show significant cryogenic deformation of the C/SiC composite mirror, which is well reproduced by a model analysis with measured properties of the bonded segments. It is concluded that the deformation is due mostly to variation in coefficients of thermal expansion among segments.

Microscopic surface structure of C/SiC composite mirrors for space cryogenic telescopes.

We report on the microscopic surface structure of carbon-fiber-reinforced silicon carbide (C/SiC) composite mirrors that have been improved for the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) and other cooled telescopes. The C/SiC composite consists of carbon fiber, silicon carbide, and residual silicon. Specific microscopic structures are found on the surface of the bare C/SiC mirrors after polishing.

Cryogenic optical performance of the ASTRO-F SiC telescope.

The lightweight cryogenic telescope on board the Japanese infrared astronomical satellite, ASTRO-F, which is scheduled to be launched early in 2006, forms an F/6 Ritchey-Chretien system with a primary mirror of 710 mm in diameter. The mirrors of the ASTRO-F telescope are made of sandwich-type silicon carbide (SiC) material, comprising a porous core and a chemical-vapor-deposited coat of SiC on the surface. To estimate the optical performance of the flight model telescope, the telescope assembly was tested at cryogenic temperatures, the total wavefront errors of which were measured by an interferometer from outside a liquid-helium chamber.

Fourier synthesis image reconstruction by use of one-dimensional position-sensitive detectors.

An improvement of Fourier synthesis optics for hard x-ray imaging is described, and the basic performance of the new optics is confirmed through numerical simulations. The original concept of the Fourier synthesis imager utilizes nonposition-sensitive hard x-ray detectors coupled to individual bigrid modulation collimators. The improved concept employs a one-dimensional position-sensitive detector (such as a CdTe strip detector) instead of the second grid layer of each bigrid modulation collimator.

Development of a gallium-doped germanium far-infrared photoconductor direct hybrid two-dimensional array.

To our knowledge, we are the first to successfully report a direct hybrid two-dimensional (2D) detector array in the far-infrared region. Gallium-doped germanium (Ge:Ga) has been used extensively to produce sensitive far-infrared detectors with a cutoff wavelength of approximately equal to 110 microm (2.7 THz).

Cryogenic optical testing of sandwich-type silicon carbide mirrors.

The experimental cryogenic performance of 160-mm-diameter silicon carbide (SiC) mirrors, one of which, a 700-mm-diameter mirror, is to be used as a primary mirror of the Japanese Infrared Astronomical Satellite ASTRO-F, is described. The mirrors are made from a sandwich-type SiC material that comprises a light porous core and a dense chemical-vapor-deposited coat of SiC. Three mirrors were manufactured consecutively, and changes in their surface contours related to temperature were measured with an interferometer when the mirrors were placed in a liquid-helium cryostat.