moore at eds.org
Fri Feb 12 08:06:33 PST 2010
On Thu, Feb 11, 2010 at 11:48 PM, Joachim Pedersen <joachimp at gmail.com> wrote:
> So, 555timers are really small ICs, which can't really push that much
> current, so you would need to have the 555 trigger some kind of power
> FET methinks. Also,
Yes I was just kinda assuming a FET in there.
> resistive heating is notoriously inefficient...
But where would waist enegery go if not in to heat?
> So how about some chemistry? The crystallization of sodium acetate
> creates quite a good amount of heat, it whats used in reuse-able
> heatpacks! Whats better, is that the reaction can be triggered by
> something like a servo connected to a uCtrler that monitors the
> internal temperature. We just need to substantially disturb the
> solution! We could have several cells of sodium acetate solution, and
> activate them in sequence as more heating is needed.
This would also have to work at low pressure 7%-1% of sea level.
> How long is the flight time? I assume you just need to stay above 0C?
> Is there data on the temperature history during last flight? Any ideas
> on a target max weight for the heating system?
We have some history. We know the temp sensor inside the G1 got down
to -11C and took a long time to warm up I have attached a graph. We
also know that at near the peek of the flight the APRS beacon was a
-20C. Our inital flights will be a 1.5h-3h but we are interested in
much longer weeks, months, long flights.
I think the big advantage of electracal is control and the ability to
store solar enegery. Thou it might be the that we should just use a
thermal mass but that costs wait which we are limited on. Initallay we
are on a 4lbs wait buget.
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