The Development and Qualification of Thermal Control Coatings for Snap Systems Page: 13 of 75
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I. INTRODUCTION
Two nuclear auxiliary power systems are currently under development for
the Atomic Energy Commission (AEC), at Atomics International (AI), a division
of North American Aviation (NAA). The 3- to 5-kwe (SNAP 2) Mercury-Rankine
power unit is comprised of a 50-kwt, NaK-cooled reactor heat source and a Hg-
vapor turboelectric power conversion subsystem (PCS). The 500-w-electrical
SNAP 10A power unit is comprised of a 30-kwt, NaK-cooled reactor heat source
and a thermoelectric PCS. The special requirements of a reactor operating in
a space environment (minimum weight, completely unattended operation in a
high-temperature, vacuum environment, etc.), create unique problems in the
development and qualification of radiation control coatings.
In February 1961, the Compact Systems Division of AI initiated an effort
for development of radiation control surfaces for the SNAP 2 and 10A systems.
A major requisite for these coating systems is that they successfully operate
for 1 yr in a space and nuclear environment. The environmental requirements
for the SNAP system space radiator coating are:
Duration 1 yr
Vacuum 1011 torr
Temperature 650 OF maximum
Nuclear irradiation 1018 nvt (fast)
109 R
Ultraviolet irradiation 1 yr
Aerodynamic heating Ambient to 700*F in 140 sec
Mechanical vibration and shock Launch stress
The various components of the SNAP systems require, basically, four types
of radiation control surfaces:
a) A coating system which is effective in rejecting internal heat and reflect-
ing solar input. The coating must operate at 6000 F for 1 yr;
b) A high-thermal-emittance coating for heat-sensitive components or heat-
treated alloys;
c) A coating which will act as radiative insulation for high-temperature
components;
d) A composite coating pattern for the SNAP 10A ejectable heat shield to
control system temperatures during launch and before reactor startup.
NAA-SR-9908
9
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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/m1/13/: accessed July 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.