[eagle] Re: Latest 70 cm Receiver Test Results

Jim Sanford wb4gcs at amsat.org
Sun Jun 10 17:48:06 PDT 2007


Dick:
Simplisticly:
  What have we seen and designed to in the past?  It would seem like 
that would be a reasonable requirement for both the payload teams and 
the thermal team.  Give the payload guys a reasonable number to start with.

Thanks & 73,
Jim
wb4gcs at amsat.org


Dick Jansson-rr wrote:

> 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.
>
> ------------------------------
> 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 ? = 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, ? = 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 ? = 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*
> kd1k at amsat.org <mailto:kd1k at amsat.org>
> kd1k at arrl.net <mailto:kd1k at arrl.net>
> ---------------------------
>
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>
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