By the say,
are there new specs for the receiver yet? Is it still expected to cold
soak to -70C? That’s close to the temperature of liquid CO2 and well below
the storage temperature of most components and way below the operating
temperature limits.
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Juan:
There has never been any
plan, specification, or thought of soaking any Eagle equipment to -70°C. The -70
number comes out of a very dynamic cooling situation that is barely possible and
probably will not be allowed. This number comes from the fact that the higher
power modules that are not conductively coupled to the spaceframe, such as are
transmitters, could numerically get to the lower temperature range if it is
unpowered or reduced power dissipation.
In a
protracted eclipse (~2 hour), the outer shell of the spaceframe will get
very cold, taking such modules as the URx down in temperature. This is a highly
dynamic situation that has not yet been modeled, and it won't be until we have a
spaceframe design on which to base such a model. Medium power modules such as
the URx will have to have its outer cover emittance in the range of ε
= 0.45 or so because it will be mounted on the thermally isolated
module mounting channels. Very low power modules, P < 1.0W, will be able to
have the very low emittance of the AlClad aluminum and their
lower temperatures will not be below ~-20°C. It is through these means that
the critical command modules will not loose their functionality during eclipse,
as I have noted previously. These numbers are not only analytical but have been
confirmed by in-flight telemetry.
The BOE numbers go as
follows:
If the spaceframe cools to
-100°C
If the URx is powered to
3.5W, ε = 0.45
If the URx is in thermal
equilibrium
Then the equilibrium
temperature would be about -48.8°C
Under these same
conditions, but with an E05 20 module that is P = 1.0W and ε = 0.04, the
equilibrium temperature would not be below 0°C. (Getting and keeping a module
emittance that low is not very probable as there are wire lead conduction terms
that affect the end result.)
There are too many "if"
statements here before on which to base a specification at this point in time,
but these are the issues that I have to deal with in trying to keep a spaceframe
alive during eclipse. Module designers, on the other hand, must also be prepared
for these kind of conditions and not expect a rosy comfortable arm chair
environment during eclipses. Eclipses will be a fact of life, as they always
have been, and I cannot make things better for you if the module power
dissipation needs to bring the module emittance off of the bottom
stop.
'73,
Dick Jansson,
KD1K
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