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Re: Design for failure?



Well, we almost got it right...
<<

Naw...your wrong.  YOu got it right.  pcsat is the future.

Robert


>From: Bob Bruninga <bruninga@usna.edu>
>CC: amsat-bb@AMSAT.Org
>Subject: Re: [amsat-bb] Design for failure?
>Date: Thu, 27 Jun 2002 16:55:57 -0400 (EDT)
>
>On Thu, 27 Jun 2002, Assi Friedman wrote:
>
> > Most spacecraft builders think about it, but never really design their
> > system to this.  So, if we build to perform, why not build to fail? A
> > dead pack could mean non-eclipse operation only, what's wrong with that?
>
>Interestingly we designed for shorted cells in PCsat.  The battery charge
>regulator was designed to give up putting any solar array current into a
>battery that had dropped more than 1.2 volts below minimum discharge.
>Thus isolating the battery from the rail once they failed.
>
>BUT since in PACKET mode, each packet burst takes a peak current (for
>one second) that is greater than the average ouput of the solar cells,
>there MUST be some battery capacity to provide that  1 second burst of
>peak energy.
>
>Once PCsats batteries get too soft to provide even that 1 second burst
>(like it did on Field Day) all you hear is the beginning half second of a
>packet and then a decaying dribble and then the TNC resets on the
>negative going voltage transient...  So we almost got it right...  WHat we
>should have done is then also had a LOW POWER mode on the transmitters
>that would not have drawn more current than was available form solar
>panels alone...
>
>AND we made all sides of our satellite have dual redundant
>wired panels (except one) so that we could survive any single solar
>panel failure....  But of course, the one panel that failed on launch was
>the unique specially configured non redundant one-of-a-kind one on the
>bottom...
>
>Well, we almost got it right...
>
>Bob
>
>http://www.ew.usna.edu/~bruninga/pcsat.html
>
>
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Robert Oler WB5MZO Houston TX


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