An estimate of the transparency of aluminized mylar 'superinsulation' was obtained by measuring the far-infrared/submillimeter wave transmittances of 3 pieces randomly selected from a 25.4μm-thick (nom. 0.001 in.) sheet of mylar that was aluminized on one side. Measured transmittance values were less than 1 x 10↑(-4) in the 100μm - 1000μm wavelength region. The emissivities of mylar and aluminum were computed from published optical constants to be, respectively, about 5 x 10↑(-2) and 2 x 10↑(-4) for temperatures near 20K and an effective wavelength of 150μm. Due to the strong attenuation of the aluminum layer, the radiant power from an elemental area on the outer surface of the superinsulation is about 10↑(4) times more significant than radiance originating within the insulating mylar layer, for temperatures near 20K. Radiant power passing through doubly aluminized mylar (the usual configuration) would be attenuated by a factor of about 10↑(-10).
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