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7. Launch Environment Exposure of A193 at Vandenberg Air Force Base
(VAFB)
A qualification requirement for the AI93 radiation control coating is that
it undergo exposure at VAFB. This environmental test includes outdoor and
indoor exposure for 30 and 90 days respectively.
These tests are complete. The 90-day indoor exposure resulted in no
change in thermal emittance or solar absorptance for the A193 coating system.
However, visual inspection indicated that the 30-day outdoor exposure caused
severe deterioration of the coating solar absorptance. The as of the exposed
coating was estimated to be ~ 0.60.
The outdoor exposure test clearly indicates that these control surfaces
must be protected from the salt air environment. Two approaches to this pro-
tection are promising: the use of a stripable tape which can be removed just
prior to launch; or the maintenance of a clean atmosphere on the system until
just prior to launch.
C. LOW EMITTANCE COATINGS
1. Pure Gold Foil
a. Radiation Properties
The SNAP 2 system utilizes pure gold foil as radiative insulation. The
foil is attached to the SS tubing or components by: 1) spotwelding, or 2) light-
weight band clamps.
Total hemispherical emittance measurements performed on pure gold
foil and Type 300 SS alloys yield the following values:
Material Temperature Total Hemispherical
(*F) Emittance
Pure Gold Foil 800-1200 0.04
SS Type 300 800-1200 0.22
Series Alloy
If the SNAP systems utilized a composite gold-SS radiation surface,
e.g., electroplated gold on SS, radiation transfer calculations would be based on
the emittance value, E = 0.04. Since the SNAP 2 system radiation surface is a
low-emittance foil wrap on SS, a new radiation relationship must be determined.
NAA-SR-9908
38
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Crosby, J. R. The Development and Qualification of Thermal Control Coatings for Snap Systems, report, September 30, 1965; Canoga Park, California. (https://digital.library.unt.edu/ark:/67531/metadc1028869/m1/42/: accessed July 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.