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



Don Ferguson wrote:


> I would think the correct design would be to automatically disconnect all
> batteries in an extreme low voltage situation. The satellite could then be
> run on solar while the batteries are charged via high resistance path and
> then connected to the buss if they charge. If a bad set is connected they
> will be automatically dropped and another set can be connected if available.
> We know the eventually every satellite will be running on solar alone,
> without batteries. We need to design for this at the beginning.

This sounds appealing, but the difficulty is that our modern spacecraft 
are now so totally dependent on their onboard computers that any power 
interruption (such as by an eclipse with open-circuited batteries) 
knocks the spacecraft out of commission until its computer can be 
manually reloaded and restarted from the ground. If an eclipse happens 
on every orbit, as it often does, it becomes rather impractical to keep 
the spacecraft going with a few volunteer command stations.

Perhaps a new computer design that carries flight software in a 
non-volatile memory and can boot and run automatically after a power-on 
reset would be the way to go. As I understand it, this is how the Mars 
Rovers operate so as to not have to run their PowerPC computers all 
night. They have ultra-low-power clocks that run continuously that start 
the computers at the appropriate times, plus they can start when 
sunlight appears on the solar panels.

The transponder power amplifiers would also have to be carefully 
designed to avoid pulling the bus voltage low even for a moment, as that 
would cause a computer reset.

Phil

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