[amsat-bb] Re: ARISSat-1 voice telemetry 00:27z 8/21/11

[Phil Karn]

On 8/22/11 9:18 PM, Greg D. wrote:
> 
> Ah, interesting.  So, values around +/- 0 mean that the battery is
> (or thinks it is) fully charged, and the satellite is running on just
> the solar panels.  Since that happens pretty quickly after start-up
> (low MET values), that certainly supports the conclusion that the
> battery has nearly zero capacity left in it.
> 
> But if it's "fully charged", there must be something else going on

I think it supports the conclusion that the battery has become an open
circuit. The voltage wouldn't get that high if multiple cells had
shorted. This is lucky for us since the satellite can continue to
operate on the solar panels when lit.

I'm really beginning to think about new ideas for satellite power
systems, especially Lou McFaddin's idea (published some years ago at the
Symposium) for a modular power system with a parallel bus. Each battery
is in a module with its own microprocessor and DC-DC converter to match
the standard bus voltage, and each is designed to remove itself from the
bus when its battery fails.

What's nice about this is that it's very easy to combine different
battery technologies and even supercaps and have the system degrade
gracefully over time. The computer would keep track of the total
available capacity, and at first it could operate all systems normally
through eclipse. As modules fail, it would shut down non-essential
systems one by one as necessary during during eclipse until the sun
reappears. The highest priority load would be the IHU memory. With some
supercaps in the mix it should always be able to keep the computer
alive. That would avoid a lot of spurious computer resets and associated
loss of information like recorded telemetry and store-and-forward messages.

-Phil, KA9Q