highaltitude.log.20090830

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[00:16] <SpeedEvil> for any reason?
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[00:21] <Laurenceb> cheap
[00:23] <SpeedEvil> seems pretty much of a muchness with others I've seen
[00:24] <Laurenceb> yeah but farnell didnt carry them
[00:26] <SpeedEvil> ah
[00:27] <Laurenceb> Im still pondering attitude determination of a spinning rocket
[00:27] <Laurenceb> thermopiles have to be despun a lot
[00:32] <Laurenceb> a photodiode horizon sensor might work better
[00:34] <Laurenceb> triggering off ragleigh scattering
[00:39] <Laurenceb> from the upper atmosphere
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[00:52] <SpeedEvil> have to be despun a lot?
[00:53] <SpeedEvil> Sun sensor and pick the right time?
[01:04] <Laurenceb> you need a sun sensing photodiode and a horizon sensor
[01:04] <Laurenceb> then you can solve for attitude
[01:05] <Laurenceb> but to get milliradian accuracy...
[01:06] <SpeedEvil> You think you can get milliradian with thermal?
[01:06] <Laurenceb> the good news is - if you have binary hozizon and sign d(solar radiation)/dt and xor into an input capture thats usable
[01:06] <Laurenceb> no
[01:07] <Laurenceb> photodiode with a 4mm lens & aperture seems to work
[01:07] <Laurenceb> - view a limb of the atmosphere and try to set a schmitt trigger to fire at 30km or so
[01:08] <SpeedEvil> hmm
[01:08] <Laurenceb> abov any clouds
[01:08] <SpeedEvil> I dunno about the assymetry of the skyglow.
[01:09] <Laurenceb> yeah
[01:09] <Laurenceb> but the theory is good
[01:09] <Laurenceb> you can add a correction factor
[01:10] <Laurenceb> just raghleigh scattering
[01:11] <Laurenceb> if the sensor is at 45 degrees or so to the spin axis
[01:11] <Laurenceb> then the duty cycle gives you elevation and the phase offset between max solar irradiation and the hozizontal gives azimuth
[01:12] <SpeedEvil> Seems one of those things you need to test a lot.
[01:13] <SpeedEvil> Would a balloon to 35km have useful info?
[01:13] <SpeedEvil> I mean a UV? sensor package
[01:13] <Laurenceb> blue
[01:13] <Laurenceb> the theory is well understood and behaved
[01:15] <SpeedEvil> yeah - I'm unsure if scattering off the variable albedo earth will screw you.
[01:16] <SpeedEvil> If you need milliradian.
[01:29] <Laurenceb> well +-10
[01:32] <Laurenceb> I think albedo is second order
[01:32] <SpeedEvil> yeah.
[01:33] <Laurenceb> hmm the main issue is raghleigh scattering is not spherically symmteric
[01:33] <SpeedEvil> Lots of random stuff starts to bite when you're wanting that sort of accuracy
[01:33] <Laurenceb> you can correct for that as you know the solar position
[01:33] <Laurenceb> but it means that sensitivity drift hurts you more
[01:34] <Laurenceb> thermopiles have a lot going for them as your seeing the tropopause temperature
[01:34] <Laurenceb> against space at ~0K
[01:34] <SpeedEvil> lot slower though
[01:34] <Laurenceb> the only thing that could screw you is tropical thunderstorms
[01:34] <SpeedEvil> 30hz vs 30MHz
[01:34] <Laurenceb> yeah
[01:35] <Laurenceb> but you can pull off some fancy manovers with the gyro
[01:35] <Laurenceb> get it stationary is various places
[01:35] <SpeedEvil> yeah
[01:35] <Laurenceb> problem is the sensor is square
[01:35] <SpeedEvil> Is it?
[01:35] <SpeedEvil> The window is square
[01:35] <Laurenceb> really need a spherical sensor
[01:36] <Laurenceb> window is circular, sensor die is square
[01:36] <SpeedEvil> The sensor is - AIUI - much smaller than the window
[01:36] <SpeedEvil> ah
[01:36] <Laurenceb> that makes it a pain
[01:36] <Laurenceb> I've decanned them to make cryo mm wave sensors
[01:36] <SpeedEvil> well - can you even get a lens that good at far IR?
[01:36] <Laurenceb> maybe
[01:36] <Laurenceb> but you dont need to lens
[01:36] <SpeedEvil> Sounds like fun
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[01:36] <SpeedEvil> Oh - a hole?
[01:37] <Laurenceb> yeah - just use the existing case
[01:37] <Laurenceb> oh well I've gtg
[01:37] <Laurenceb> cya
[01:38] <Laurenceb> the only reason of the lens with a photodiode is to just see the top few tens of km of atmospheric glow
[01:38] <Laurenceb> and avoid seeing clouds
[01:38] <Laurenceb> with thermopiles you dont have that issue
[01:38] <Laurenceb> unless its tropical thunderstorms
[01:38] <Laurenceb> most other weather is pretty invisible to them from space
[01:38] <Laurenceb> gtg, cya
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[10:32] <m0tek> rjharrison_home: can you remind me of the mega sucker you use to hold the eeepc on the car dash? i have an expense allotment and i'm not afriad to use it
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[13:15] <Hiena> 'afternoon!
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[22:21] <rjharrison_home> any usesers of Eagle on here.
[22:21] <rjharrison_home> any users of Eagle on here?
[22:21] <rjharrison_home> I'm wondering id you can get a parts list for a schematic
[22:22] <rjharrison_home> like a shopping list to tick off against to make sure you have ordered everyting
[22:24] <natrium42> there might be a BOM button
[22:24] <natrium42> i usually just go through the schematic...
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[23:04] <rjharrison_home> thank natrium42
[23:04] <rjharrison_home> thanks
[23:05] <rjharrison_home> I'll have a look failing that compare to the schematic
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[23:45] <rjharrison_home> Just the abs pressure sensor to connect now http://www.robertharrison.org/svn/filedetails.php?repname=the-icarus-project&path=%2FIcarus+III%2Feagle%2FIcarus+III%2FIcarus.pdf
[23:46] <SpeedEvil> :)
[23:50] <rjharrison_home> Nights all
[23:50] <rjharrison_home> See you tomorrow SpeedEvil
[23:50] <rjharrison_home> \quit
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[00:00] --- Mon Aug 31 2009