Kilowatt Isotope Power System, Phase II Plan. Volume IV. Teledyne FSCD vs GDS Page: 115 of 264
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2. 5. 2.8. 2" Fibrous Insulation
The fibrous insulation Min-K TE -1400 (Johns Manville) is used to support the heat
source assembly at its ends and simultaneously limit heat losses to a minimum value.
The location and description of this insulation is presented in Section 2.5. 1. 2. The
load bearing capability of Min-K TE-1400 is utilized to apply a preload to the heat
source assembly. This preload, plus the interlocking shape of the insulation discs,
serves to positively locate the heat source during the launch vibration environment as
well as steady state space operation. No preload force is required once the system
stabilizes in orbit, however.
A number of insulating materials were considered for the end discs. Load bearing
capability, low thermal conductivity, and suitability for long-term use in a vacuum
were the principal criteria used in selecting the Min-K TE-1400. Table 2. 5. 2. 12-I
presents certain physical properties of and the results of thermal conductivity testing
of candidate materials. This data was obtained from ASTM-C177 guarded hot plate
tests performed by Dynatech R/D Company under contract to Teledyne Energy Systems
for the Selenide Isotope Generator (SIG) program.
Preliminary tests of the load bearing capability of Min-K TE-1400 insulation have
been completed by TES for the SIG program. Insulation specimens were tested with
a 1472*F hot face and 300*F cold face and an initial compressive stress of 150 psi.
The load retention was continuously monitored. These preliminary test results indicate
that after about 10, 000 hours the load capability of the insulation is approximately 40
to 45% of the initial value.
Choice of Min-K TE-1400 was based on several factors. First, among load bearing
fibrous type insulations the Min-K insulations possess the lowest thermal conductivity
properties. Second, the temperature capability is within the range of anticipated hot
side temperatures. Third, the reported load bearing capability was adequate to provide
heat source support loads. In addition, the Min-K TE series of insulations were
developed especially for use in thermoelectric generators, where low outgassing and
low levels of impurities are desirable.
Slabs of Min-K are purchased from the manufacturer, Johns Manville Corporation.
These slabs are then machined to the required shapes. Vacuum bake-out of the in-
sulation at or near normal operating temperature assures removal of all moisture
and volatile impurities present in the insulation. At assembly, spaces, joints and
instrumentation wire routing grooves in the Min-K arc stuffed with a high temperature
micro quartz insulation wherever practical. Material certification from Johns Manville
assure slab quality.101
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Kilowatt Isotope Power System, Phase II Plan. Volume IV. Teledyne FSCD vs GDS, report, March 15, 1978; Timonium, Maryland. (https://texashistory.unt.edu/ark:/67531/metadc1055866/m1/115/?rotate=270: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.