[eagle] Re: Module Temperatures

Juan Rivera juan-rivera at sbcglobal.net
Tue Aug 28 13:05:35 PDT 2007


Dick,

That's fantastic news and will make a huge difference in my ability to get a
sound night's sleep!  As you know, the SAW filters in the existing 70 cm
Receiver are rated at a minimum operating temperature of -35C and the
minimum storage temperature wasn't much lower.  This should mean that John
can return to a one PCB design instead of having to split the receiver into
two separate enclosures.

73,  Juan - WA6HTP


On 8/28/07, Dick Jansson-rr <rjansson at cfl.rr.com> wrote:
>
>  Juan & John:
>
>
>
> I have finally been able to achieve some analytical results for projecting
> the temperatures of Eagle modules after two hour and three hour eclipse
> periods of no-solar heating. This has taken some time as I was struggling
> with the proper use of the SINDA software and had to call for some help –
> which is why we pay money for the license, it comes with help when needed.
> (I should also note that with modern versions of this software and a pricey,
> but fast and capable, Dell computer, these analytic runs only required 18
> seconds of real run time!)
>
>
>
> Nevertheless, I have been able to get some believable modeling results.
> The spacecraft model used is what I now call "Small Eagle", the formerly
> proposed, but rejected 600x600x435mm spaceframe structure. While this is not
> as large as our currently planned hexagonal structure, the equipment bays
> are just about the same size as the larger spaceframe. I ran the model with
> one of the E05 20, 125x180mm, modules with coatings with an effective
> emittance of about 0.45, rather than 0.04, as would have to be done for
> the URx module. There was essentially no power dissipations in any module,
> at the most about 20mW in a few modules. This is granted to be an abnormal
> situation, but I wanted to see what happens. A later run was made with only
> a total spacecraft power dissipation of only 7mW were only lower by 0.1°Cto
> 0.2°C lower temperatures.
>
>
>
> Modules started out at temperatures of +20°C and the spaceframe core
> structure at +10°C. The propellant tank was empty so it did not contribute
> any large thermal mass to delaying the cool-down. After two hours of eclipse
> the module temperatures were -5.2°C to -5.4°C (with the high emittance
> module being cooler), and after three hours of eclipse the module
> temperatures were -15.9°C to -16.2°C. The spaceframe core structure
> (equipment panels) were down to -10.2°C and -19.4°C respectively. For
> these cooling periods, the spacecraft outer skin temperatures ranged from
> -35°C down to -55°C. The deployed solar panels became a bit chilly, down to
> -113°C.
>
>
>
> A subsequent SINDA run was made with some kind of useful power
> dissipations in modules – 0.5W to 1.0W – not large but supposedly enough
> to keep things from getting out of hand, and with a total spacecraft
> dissipation of 16.5W. The two hour eclipse temperatures ran from -3.4°C (
> 1.0W) to -3.9°C. In three hours of eclipse the module temperatures were at
> -13.3°C down to -14.0°C. In other words, these levels of power dissipation
> did not significantly warm the modules. The spaceframe core temperatures
> were at -8.0°C and -16.3°C respectively., just a few degrees warmer.
>
>
>
> What this data tells me is that specifying the "cold" temperature of a
> module does not have to be much lower than -20°C, and if it is operating at
> all they can be only a little higher. Cold module temperatures certainly do
> not need to be in the -60°C range. Beyond these statements, I shall not
> presume to be a specification writer.
>
>
>
> '73,
>
> Dick Jansson, KD1K
>
> kd1k at amsat.org
>
> kd1k at arrl.net
>
>
>
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