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Re: Re:Re: Re: The hard questions..



I would like to put in a few comments on this issue.
As the P3D spacecraft integration manager I know the inner workings of  
the spacecraft as well as anybody. I personally put a lot of the wiring  
and designed the battery switching system.
Stan wood and I have ran extensive tests on the residual battery cells  
that were not selected to use on the flight Auxillary battery packs.  
Our tests indicate that there would not have been a large spike of  
current if the batteries were paralleled even though the Aux. batteries  
were discharged. Our tests also indicate that the batteries would  
recover just fine after charging. We therefore believe that if the main  
batteries open up or whatever is shorting the batteries opens up, then  
the Aux batteries will be able to serve the purpose they put on the  
spacecraft to do.

As to looking at the sequence of what happened, I think Stacey did  
exactly what any of us would have done given the information he had to  
work with.

During the design stage of P3D we had long discussions on how the  
battery switching relays should work and whether there should be a  
possibility of having no batteries on line. We eventually decided that  
we would preclude that possibility. This decision was based on the fact  
that there are no  solar panels on the top and bottom of the  
spacecraft. That leaves the possibility that you could get the  
spacecraft oriented in such a way that there would  no power available.  
We decided that  would not be a good idea. This very problem happened  
to the NASA SOHO spacecraft about the time we were making this  
decision. In that case they almost lost the SOHO forever.

I support Stacey on what he did and would have probably done exactly  
the same thing.

Lou McFadin W5DID
P3D Integration manager

On Feb 16, 2004, at 8:16 AM, Stacey E. Mills wrote:

> Kevin said...
>
>> >If we had been clairvoyant we would have probably charged the aux.  
>> battery
>> >and taken the main battery off line.
>>
>> you had earlier mentioned that the command team had noticed battery  
>> anomalies
>> several months ago...
>
> Correct, and that had stayed "stable" for quite a while.  I was  
> speaking of the rapidly deteriorating final scenario.
>
>> > Charging the aux. battery would have accomplished nothing unless the
>> > shorted main battery were also taken off-line.
>>
>> If the aux battery would have been completely charged might it not  
>> have dumped
>> enough energy into the main to possibly burn open the dendrite  
>> shorting a
>> cell?
>
> ...maybe, I doubt it though.  We'll never know for sure.
>
>>  Or  having the aux battery  fully charged you may have been more  
>> prone to
>> "cut loose" the main  as you were watching it fail since you would  
>> have known
>> that you had a good fully charged aux...
>
> The aux. battery would have come up to working voltage virtually  
> instantly, so that really wasn't a factor.
>
>> In hindsight at the time of failure,cutting both batteries open might  
>> have
>> been yet another option, since you could then catch the sat in  
>> sunlight and
>> look at what was going on with both batts before committing to one or  
>> the
>> other... but there may be things I'm not aware of that would have   
>> prevented
>> this from working...
>
> That command is not an option.  The hardware prevents taking both  
> batteries off-line.
>
>> personally I think the relay design is poor  and connecting a dead  
>> aux is not
>> much better... diode isolation even though it costs you a voltage  
>> drop  would
>> have been better, but I know then you couldn't try and save a set of
>> batteries until later... every design has tradeoffs.
>
> The diode option was extensively debated during construction.
>
>>      I for one no know of no company, group, individual, or doctor...  
>>   that
>> doesn't do a post-mortem after something goes wrong...   to learn  
>> from what
>> has happened and to see if anything could have been done differently   
>> in the
>> future. But there is no reason for anyone to wrap themselves in self  
>> pity or
>> to martyr themselves as being to blame, for that is non-productive...  
>> but to
>> just say it was "inevitable" and lets move along to the next sat  
>> without
>> reviewing all of the possibilities and options  is equally  
>> non-productive.
>
> I am not attempting to be a martyr or engage in self-pity.  The  
> "inevitable" in my comments does not refer specifically to this  
> incident.  It refers to the fact that nothing lasts forever.  Every  
> satellite and every person must eventually die and blame is not always  
> a component of that event, although many of us have a strong tendency  
> to try to make it so.  I don't personally believe that we have seen  
> AO-40's ultimate death.  It was certainly not my point that we should  
> "move on without reviewing."  Amsat groups all over the world are  
> analyzing this incident and considering applications  to future  
> satellites.  Questions have already been posed about P3-E's battery  
> configuration, based on this incident.   However, there is a right way  
> and a wrong way to construct a review process.  These are a weekly  
> function in my business.  Blaming, finger-pointing, inflammatory  
> rhetoric, etc. are not productive.  Productive reviews are at the  
> process level.  Any review of AO-40 will always be heavily colored by  
> the unknowns of the 400n incident which caused significant mechanical  
> distortions, heat, pressure, etc.  We have no way to know the extent  
> of these damages.  It seems quite likely that they played a part in  
> the battery failure.
>
>
>
> --  
>   
> _______________________________________________________________________
>  Stacey E. Mills, W4SM    WWW:    http://www.keplerian.com
>   Charlottesville, VA     PGP key: http://www.keplerian.com/key
>   
> _______________________________________________________________________
>
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the  
> author.
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>
>
Lou McFadin
AMSAT BOD
AMSAT Orlando Lab Manager

----
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