[amsat-bb:74915] Re: AO-40 Update, 2004-02-03

["Stacey E. Mills" <semills@xxxxxxxxxxxx>]

>   Part of this waiting game is knowing what the exact cells are composed of
>that you are waiting to open, based on your description and pictures of the
>main and aux banks, 
><http://www.amsat.org/amsat/features/p3dpix2/photo4.jpg>http://www.amsat.org/amsat/features/p3dpix2/photo4.jpg 
>
>,we can see that the cells are cylindrical.
>
>  Yet it seems that what was built differs from what was planned,
><http://www.amsat.org/amsat/sats/phase3d/thermal.html#Power>http://www.amsat.org/amsat/sats/phase3d/thermal.html#Power 
>, I quote..
>" The Main Battery is composed of 20 cells of 40 Ahr capacity, for a 22-28 
>VDC
>supply. These rectangular cells are from a terrestrial application, but have
>been very well characterized for space service."   rectangular cells....

>So I'm still wondering  since it looks like the type of main battery was
>changed, can anyone tell all of use what is really flying? what's is the
>brand and model of the cells.

Unless I put <conjecture></conjecture> around my posts, you can consider 
them to be fact.  The batteries seen in that very old picture were used for 
ground test work, something you don't want to use the flight batteries 
for.  The flight batteries are as I have stated, rectangular, 40 amp/hour, 
3 packs, metal enclosure, etc.  I was there at the final integration in 
Kourou and saw them in place.  I believe I remember who made the batteries, 
but I'll look it up to be sure.  The model number should be available as 
well. Likewise, some older pictures or drawings may show three aux. 
battery. packs.  There were only two at launch.

[another post]

>Lets say all our present hope if futile and the sat drifts for 10 years
>and then something breaks loose and
>it does an Ao-7 on us.  Without the batteries and with the panels closed
>will there be enough power to
>drive the wheels to right the bird again?

If you look back at my last post, I indicated that it would take 4 years to 
drop from 3.5 RPM to 3.0 RPM.  It will take slightly longer to drop from 
3.0 to 2.5 RPM and slightly longer still to drop from 2.5 to 2.0 RPM.... 
(>12 years for 3.5 -> 2.0 RPM), and we can still magnetorque at even 1.5 
RPM (or possibly lower if we use some different software).  So even 16 
years out we should still be spin stabilized with enough RPM to trigger the 
magnetorquers.  By then our ME/heading estimates, etc. will have diverged 
greatly from reality, but it doesn't really matter.  We'll be spinning, and 
based on a few orbital determinations of optimum signal, direct squint 
measurement, earth sensors, solar angle, pictures, etc, we would be able to 
find our attitude and torque back to where we want to go.  There is no 
reason to use the momentum wheels for this purpose.  They were designed for 
3-axis mode.  As long as the satellite is spinning ANY, they can only 
slightly change the spin rate, they cannot change the attitude when the 
satellite is spin stabilized.  When we first encountered problems with the 
batteries, we changed the spin rate from 2.5 to 3.5 RPM as a safety 
precaution.  This turned out to be a very good move.





-- 
  ________________________________________________________________________
  Stacey E. Mills, W4SM    WWW:  http://www.keplerian.com
    Charlottesville, VA     PGP key: http://www.keplerian.com/key
  ________________________________________________________________________  

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