High altitude balloon payload, from Sable-3 discussion Options

[JRehling]

[...]

[djellison]

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

[JRehling]

[...]

[djellison]

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

[rlorenz]

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.

[djellison]

, 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

[rlorenz]

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.

[jamescanvin]

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

[djellison]

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

[djellison]

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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[djellison]

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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[djellison]

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

[rlorenz]

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.....

[lyford]

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.....

[rlorenz]

Any chance this was recorded for web broadcast?
I know we are getting spoiled.....

It was - I signed a release form, at least. But I don't know when AGU will
put it on-line...