Reg readers fret over misty-eyed LOHAN Our heads-up last week on the Vulture 2 spaceplane's miniature Raspberry Pi camera (Picam), prompted some readers to express concerns that we were heading for trouble in the imaging department. Here's the camera in question... A close-up of the Picam ...and here it is glued into the underside of the aircraft's nose: The …
In general the Stratosphere is relatively dry and often at sufficiently low temperatures for most atmospheric water to be in the form of ice so generally misting should not be too much of a problem.
LOHAN should be taught about in schools as it is a project with a big accent on fun while having the ability to produce good science.
One commentard suggested it could end in a fireball, I am a lover of large explosions and fireballs but in this instance I would hate to see such an ending, particularly for the intrepid playmonaut who like astronauts are heroes in their own right.
I have subsequently discovered my father had a lot of experience in mist-proofing camera lens assemblies for use at high altitude. (Don't ask questions, I'll tell you no lies) The solution was to machine on purging ports so that the lens assembly could be purged with dry nitrogen before a mission... something rather impracticable with this Pi camera as it's so tiny...
Fogging when going from warm to cold is not an issue, frosting, may be, but not fogging. I don't think LOHAN will fly for long in icing conditions (clouds at 10 to 15 thousand feet), so that risk should be minimal.
Fog (condensation) will occur on coming back from cold to warm and if the transition is gradual (as it will be) and there will be a lot of airflow, it should still not be an issue even then.
If it is even a remote concern a fix doesn't need to be complex since it's effectively a point to heat. A few turns of nichrome wire or even a couple of resistors would do the job nicely. See e.g. http://www.skyandtelescope.com/howto/diy/3304231.html for a practical example of solving the same issue in a slightly different context.
You've got a plastic bezel around the lens which decreases efficiency, but of course the lens is far smaller to start with, so pluck a figure of 1W-ish power out of the air based on that article. From the 5V power for the Pi that's be a couple of ½W 47R resistors wired in parallel, one each side of the lens assembly. However, current draw is an additional 213mA which may need to be accounted for.
Have a look at re-windable e-cigarette coils - if you can make a low enough resistance one, you should be able to get a couple of hours of of a standard 1000mah cell (which weights somewhere in the region of a hundred grams or so).
Might be worth a punt if it's of real concern, and the bits to test with are cheap enough.
Steven R
The camera already draws approx 200mA at 3.3V so it heats itself, so if I were worried (which I'm not) I could just leave the camera on all the time.
I've flown these cameras with very little insulation, and sometimes with none. They've never fogged. It's not a problem and doesn't need a solution.
Dave
The amount of complexity for small enclosure heating can be absolutely minimal.
These guys make self-regulating thermistor heating elements in various sizes with transition temperatures down to 40C. Basically choose the block size for the correct power dissipation. Apply suitable voltage. The block will rise to around 40C at which point it will start to turn off. Lower outside temperature, block will cool and take more current to compensate. For an external lens, apply an annular washer of copper or aluminium to lens with suitable grade of epoxy, attach thermistor with silver loaded epoxy.
The entire circuit consists of battery, thermistor and two pieces of wire.
Not needed in this case but offered as a suggestion to anyone who wants a simple demisting solution for small electro-optical enclosures.
Shouldn't be a problem again.
(Reaches for Apollo-13 video...)
Seriously, the team, and other flights have proved it. A couple of 470Ω 'torched' by 4v (it will be, when it gets cold) jobbies aint gonna do it, bit like warming an igloo with a candle.
It's the temperature differential rather than the moisture, surely? LOHAN's got plenty of time to get it up and get used to it before the elastic snaps (or whatever).
Bit like driving my mates LADA in Finnish winter. The heater's eff-all use, inside ▒, outside ░ more-or-less the same. Fergerrabahtit.
BMW passes me in -40, frantically wiping.
I suddenly had this image of a microflame miniature blow-torch solution for the heating problem. If you want to go down in flames, that's one way of doing it properly ;-)
On a more serious note: love the LOHAN project, and indeed, it should be shown in schools.
Icon, because, well, obvious innit?
as title, but then again, I'm always a bit of a pessimist. I appreciate the article to specifically adress the issue! The reason of my remaining doubt is that CHAV was a relatively low speed vehicle. LOHAN will have to survive a lot more forces and a lot higher speeds.
In any case, there is no way back now. All that remains to do now is to wait and see how it performs. Although I'm sure flights aren't cheap I'm sure there can be more than a single flight if it ever comes to it. (Though a second or more flight might take a while to save up)
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