[Space] Heating

Joachim Pedersen joachimp at gmail.com
Fri Feb 12 01:28:37 PST 2010


> I like the idea of a controlled chemical reaction.  We'd discussed hand
> warmers already, but dismissed those because of the need for oxygen, which
> is obviously limited in that thin atmosphere
Yeah, this is a phase change (kinda) and precipitation, no need for O2
here... The implementation of these in the commercial world consists
of a sealed plastic bag with a rough metallic plate that is disturbed
to initiate nucleation. They can be reused until the plastic bag
breaks down. The heat generated is due to the latent heat of fusion.

http://en.wikipedia.org/wiki/Sodium_acetate#Heating_pad

http://www.helium.com/items/477007-the-chemistry-of-reusable-heat-packs

-Joachim
------------------------------



On Fri, Feb 12, 2010 at 01:11, Christie Dudley <longobord at gmail.com> wrote:
> Well, if we're trying to avoid condensation, then we'd actually want to keep
> stuff above the dew point.  Not sure what that would be at that level, and
> it probably varies depending on clouds, etc.
> The camera lens would probably be the biggest consumer of heat.  It
> generates no heat itself, has limited insulation opportunity and has
> significant degradation from cold.  Although it doesn't completely stop
> working, the current theory is that the camera itself stopped because off
> condensation.
> I like the idea of a controlled chemical reaction.  We'd discussed hand
> warmers already, but dismissed those because of the need for oxygen, which
> is obviously limited in that thin atmosphere.  I've cc'd Ben Rupert, a
> recent NB convert who knows quite a lot about chemistry to see if he might
> be able to help with this discussion.
> Christie
> _______
> "The road of excess leads to the palace of wisdom." -- W. Blake.
>
> The outer bounds is only the beginning.
> http://www.flickr.com/photos/genriel/sets/72157623376093724/
>
>
> On Fri, Feb 12, 2010 at 9:10 AM, Christoph Maier
> <cm.hardware.software.elsewhere at gmail.com> wrote:
>>
>> On Thu, 2010-02-11 at 23:48 -0800, Joachim Pedersen 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, resistive heating is notoriously inefficient...
>>
>> It is, because you lose a lot of heat in the controller, in particular
>> if you don't use PWM.
>>
>> However ... we want to heat some stuff up to the point where transistors
>> are cozy and warm, not higher.
>> The most efficient way to do this is to use the regulating transistors
>> _themselves_ as heating elements - mounted together with the devices we
>> want to heat on a good thermal conductor (i.e., a block of aluminium),
>> and wrap a good thermal shield (that also serves as padding to prevent a
>> reasonably solid piece of metal hitting something at landing) around it.
>>
>> The electronics would contain power transistors as heating elements, an
>> adjustable temperature regulator, e.g.,
>> LM56 or LM57 [ http://www.national.com/cat/index.cgi?i=i//73 ,
>> http://www.national.com/cat/index.cgi?i=i//71 ]
>> and a few resistors and capacitors.
>>
>> Christoph
>>
>>
>>
>>
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>
>


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