windows frosting at high altitude

Hello all
We are launching a camera up in a high altitude balloon (no rockets invovled but high altitude, I figured you all know about that) to
hopefully 80 000 feet. We are worried about frost forming on the windows and blocking the veiw.
This is going to be a long flight, on the order of 3 or 4 hours, so sustained power consumption (heater) might be an issue, but there is capacity for batteries if this is the best idea. This is still in the concept stage, so different materials for the window are a definate option.
We have already tried a couple of things that do not work, including those silica gel drying salts, and a presurized window box.
Any previous experiences with this sort of thing, or If anyone has some ideas, I would be delighted to hear. Thanks in andvance for all your help
Jack
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Hello all
We are launching a camera up in a high altitude balloon (no rockets invovled but high altitude, I figured you all know about that) to hopefully 80 000 feet. We are worried about frost forming on the windows and blocking the veiw.
This is going to be a long flight, on the order of 3 or 4 hours, so sustained power consumption (heater) might be an issue, but there is capacity for batteries if this is the best idea. This is still in the concept stage, so different materials for the window are a definate option.
We have already tried a couple of things that do not work, including those silica gel drying salts, and a presurized window box.
Any previous experiences with this sort of thing, or If anyone has some ideas, I would be delighted to hear. Thanks in andvance for all your help
Jack
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snipped-for-privacy@hotmail.com wrote:

Jack,
have a look at dew heaters used on telescopes - might be sufficient to keep the lens clear, especially if you toggle it on / off on a timer to reduce power consumption. Try Woodland Hills camera or Adorama for good pricing & service.
HTH
G.
--
Graham J. Platt
graham (a) bowhunter (d) demon (d) co (d) uk
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Jack,
Do a search for EOSS, Edge of Space Society, in Denver. They have been doing this for about 10 years, and have a lot of experience. Hope you have reat success. If I can help, please E-mail me.
Ed
wrote:

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snipped-for-privacy@hotmail.com wrote:

Race cars have a rotating window that cleans/wipes in the rear. You could heat the whole thing too.
Jerry
--
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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try this site http://www.hamtv.com/info.html
Misha VE9MTB TRA L-1
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Jack, You shouldn't need heaters or wipers. I did my own little high altitude balloon project a few months back, and did some research prior to launching it. Unless you float through some really thick clouds on the way up, you should be fine.
The reason is that the lens of the camera will generally stay warmer than the surrounding air. Condensation generally occurs when air is cooled to the point where it's water content is greater than the amount of water it can hold for that temperature...
For example, if you have air at 70F and it's 80% saturated, you can cool it a few more degrees until it becomes 100% saturated. Any further cooling after that will result in condensation.
So, due to the thermal capacity of your camera (well, really lens assembly which is warmed via conduction and radiation from the camera), the lens should be atleast a few degrees above the ambient temperature ON ASCENT. During descent, due to high convection coefficients and reintroduction to warm temperatures of the lower atmosphere, the lens may be colder than ambient air for a period. I don't think you're that worried about descent pictures though... most of mine were pretty blurry until it slowed around 40kft.
One thing you might consider is using a camera that has a lens cover that shields the lens when the camera's off. I used the kodak ke60 and samsung 80ti, both of which had lens covers and were electronically controlled and worked great.
Feel free to go here for more info: www.geocities.com/achilles03/hab.htm
Hope that helps, Dave
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