High altitude balloon payload, from Sable-3 discussion |
High altitude balloon payload, from Sable-3 discussion |
Oct 28 2007, 07:16 AM
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#151
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
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Oct 28 2007, 08:41 AM
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#152
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
I don't think what you describe would work. The ballon, once inflated in the ground, maintains a similar ammount of lift for the entire flight, because the maths end up roughly cancelling out between the outside, inside pressures and air density. If you look at the graphs of altitiude over time for these things, they're very close to a straight line. Thus - a ballon that was under inflated at the ground ( and thus not providing any real lift ) would be larger but still providing no lift @ 100kf.DougI don't think what you describe would work. The ballon, once inflated in the ground, maintains a similar ammount of lift for the entire flight, because the maths end up roughly cancelling out between the outside, inside pressures and air density. If you look at the graphs of altitiude over time for these things, they're very close to a straight line. Thus - a ballon that was under inflated at the ground ( and thus not providing any real lift ) would be larger but still providing no lift @ 100kf.Doug
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Oct 29 2007, 07:17 AM
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#153
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
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Oct 29 2007, 08:13 AM
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#154
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
Yup - for one of those utterly enormous balloons that looks like what happens when a kitten gets hold of a roll of cling film
KISS / BISEOGE etc etc. Get to 80-100kf, get down. That's the principle here. Doug |
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Nov 3 2007, 01:50 PM
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#155
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Member Group: Members Posts: 610 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
http://www.unmannedspaceflight.com/index.p...20&start=20 We began talkin about a UMSF balloon - and who know what might happen if enough people think about something hard enough, thoroughly enough and long enough. Apparently I wasnt paying attention when this thread evolved...... Anyway, I'd be happy to help - I may have some relevant skills and experience (see, e.g. my instrumented frisbee http://www.lpl.arizona.edu/~rlorenz/frisbee_mst.pdf) I have also been hacking cameras to be PICAXE-controlled (for study of dust devils) If I can make a couple of plugs for nonimaging data, I'd love to see at least 3-axis acceleration data (ideally gyros too), maybe sun/horizon sensing etc. too. I can make design suggestions, or build/provide (depending on timing). Some very nice SD-card or USB-stick datalogging boards that can be stamp- or picaxe driven these days. Could have a very nice instrument package for 100g all-up. |
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Nov 3 2007, 07:49 PM
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#156
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
, I'd love to see at least 3-axis acceleration data (ideally gyros too), maybe sun/horizon sensing etc. too. Ditto - the entire turbulance-thru-cloud issue that we've talked about would be an interesting way to go. With SD / CF then we could have a high enough data rate to make it usefull, whilst having the space for a long flight (longer than a frisbee anyway ) Perhaps LDR's might work as inverted sun sensors? One on top/4xsides - then could technically interpolate a sun position..ish? Doug |
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Nov 4 2007, 12:29 PM
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#157
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Member Group: Members Posts: 610 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
Perhaps LDR's might work as inverted sun sensors? One on top/4xsides - then could technically interpolate a sun position..ish? Doug Actually LDRs would not be ideal since they are rather nonlinear (not sure on their temperature dependence too, which given nonlinearity would be a tricky data reduction problem) ; if the package were to be spinning during parachute descent, the response time of LDRs could become a factor too. Much better to use a planar photodiode (only $1 or so) in current mode - photocurrent is linear with flux so you get a very near to cosine angle response (deviates slightly due to reflection/matching effects with the plastic cover). Since it is a current device, you can use a microcontroller digital channel to time a capacitor charge-up, without even needing an Analog-to-Digital converter. With my frisbee work on planar photodiodes I don't think I could do much better than 5 degrees (and spin is helpful, gives you a lot of datapoints). To do better you'd want a slit-mask type or something that images the sun position. |
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Nov 5 2007, 09:23 AM
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#158
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Senior Member Group: Moderator Posts: 2262 Joined: 9-February 04 From: Melbourne - Oz Member No.: 16 |
I know Ralph was trying to plug non-imaging data but I would have thought that the simplest way to track the sun would be to have a small camera pointing at a sundial.
James -------------------- |
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Nov 5 2007, 10:27 AM
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#159
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
That's quite a heavy and data-expensive way of doing it though - as well as requiring a lot processing after the flight...and assumes a clear day for the bottom, say, 1/3rd of the flight. Sensors + maths would, I'd have thought, done a better job
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Nov 10 2007, 12:19 AM
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#160
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
I have a Picaxe data logger working - with Temp, LDR and Humidity (a 'maybe' on the humidity at the moment)I have a Picaxe data logger working - with Temp, LDR and Humidity (a 'maybe' on the humidity at the moment)
Just raw figures, not values yet - but I held the temp sensor, breathed on the humidity, and 'showed' my laptop screen to the LDR a few times - and stuff changed Doug |
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Nov 10 2007, 10:45 AM
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#161
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
An overnight run.
Blue line is the LDR - you can see a couple of overnight triggers of our security light, followed by the increase of the sunlight kicking in at dawn Green is temp - chilled within 10 minutes when I put it in the conservatory, then it rose slightly when the sun rose. The orange is humidity..I'm not sure what, if anything, is going on there. 9/10ths of 4/5ths of nothing. To be honest, I may have cooked it last night when wiring it up - there's no indication which way round it should be wired up. I'll do some testing using the kettle - see if I can switch up to 100% humidity etc etc. Doug |
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Nov 28 2007, 02:45 PM
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#162
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
Just an update - things have been slow, real life has been getting in the way. For <£10 I've just picked up a Vaisala RS80 radiosonde - the typical weather balloon payload launched hundreds of times a day around the world. Thought it'd be an interesting research artifact to have a look at, maybe even steal it's sensors
http://www.vaisala.com/weather/products/so...adiosondes/rs80 Doug |
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Dec 16 2007, 04:56 PM
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#163
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Member Group: Members Posts: 610 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
Just an update - things have been slow.... Just an update - things have been real busy (AGU - managed to work 'All your base are belong to us' into my Sagan lecture!) I did just get a few of those $20 1.3MP keychain cameras from Walmart. Took one apart (even this tiny package is mostly plastic case) and will let you know when I get it under PICAXE control..... |
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Dec 16 2007, 07:39 PM
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#164
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Senior Member Group: Members Posts: 1281 Joined: 18-December 04 From: San Diego, CA Member No.: 124 |
AGU - managed to work 'All your base are belong to us' into my Sagan lecture! Any chance this was recorded for web broadcast? I know we are getting spoiled..... -------------------- Lyford Rome
"Zis is not nuts, zis is super-nuts!" Mathematician Richard Courant on viewing an Orion test |
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Dec 18 2007, 12:37 AM
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#165
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Member Group: Members Posts: 610 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
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