Feasibility of Isotopic Power for Manned Lunar Missions. Volume 1. Summary. Page: 44 of 61
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addition, very short duration zero g condensation-tests have been per-
formed in KC-135 aircraft and in drop tests. These tests have all been
positive and indicate that such a condenser can be built and will operate.
Some question still remains, however, as to film stability in the zero g
Thompson proposes to use Haynes 25 tubing throughout the conver-
sion system. They further propose to braze the Haynes 25 condenser
tubing to the aluminum skin. From a metallurgical standpoint, it is
felt that such a braze represents a significant step beyond current tech-
nology. Since the inlet temperature is 5750 F to the condenser, there
is further doubt that an aluminum skin section would have sufficient
strength at this temperature to support the radiator section. A Haynes
or stainless steel skin section for the mercury Rankine radiator would
add significant weight to the system.
To summarize the problems associated with the mercury Rankine
system, the Martin Company feels that containment of liquid mercury
at the specified temperatures still represents a problem in this cycle.
Mass transfer of material from the hot area to cooler portions of the
system, such as the turbine blades, the condenser or pump, could pre-
sent a serious problem to efficient system operation. The vapor quality
also remains a significant problem. It is further felt that insufficient
analysis has been performed to adequately design the boiler and con-
denser radiator system. There is inadequate evidence to prove that
tapered tube condensation can be accomplished in a zero g environment.
5. Dowtherm-A Rankine Cycle
The Sundstrand Corporation has proposed the use of a Dowtherm-A
Rankine cycle to fulfill the power requirements for the Apollo mission.
This system has certain significant advantages which make it quite at-
tractive for use with an isotope heat source. The working fluid temper-
ature at the turbine inlet is 6500 F. This allows a fuel temperature of
approximately 17950 F to be achieved, thus assuring safe operation.
The specific problems associated with this system are discussed here.
a. Polymer formation in working fluid
Throughout the history of the organic reactor program when biphenyl
was considered as a moderator-working fluid, pyrolytic and radiolytic
polymer formation has been considered a problem. Sundstrand feels that
a system can be operated with as much as 5% high molecular weight
polymer present in the working fluid. To be on the safe side, however,
they have stated that a design objective of less than 1% would be con-
servative. Figure 2 shows the available information on polymer forma-
tion in biphenyl and Dowtherm-A as a function of temperature. The
curve shown is above nearly all of the experimental points and has been
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Feasibility of Isotopic Power for Manned Lunar Missions. Volume 1. Summary., report, January 1, 1964; Baltimore, Maryland. (https://digital.library.unt.edu/ark:/67531/metadc1032333/m1/44/: accessed May 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.