High altitude balloon payload, from Sable-3 discussion Options

[djellison]

The envelope itself is arguably the easy part. Buy it - fill it - launch it. They're a commercially available part that doesn't need that much thinking about.

The stats are here : http://www.kaymont.com/pages/sounding-balloons.cfm : you over fill compared to those stats slightly - and get a better lifting capacity - but you reduce your ceiling as a result.

Oh - and the chances of flying me on something like that to 14km.....slim....unlike me

Doug

[jamescanvin]

OK a few simulations of camera coverage.

Two cameras, one landscape pointed horizontally, one portrait, pointed 45 degrees down both normal 35mm field of view. Take one image with each and here is the coverage on a 360x180 degree equirectangular projection.



Rotate and swing to the payload, 30 degrees looks about right from a lot of images I've seen from other attempts.
Take 25 images per camera (one every 15 seconds for ~6 minutes say) and you'd be unlucky not to get a 360 and most terrain should be covered twice.



Coverage tends to improve (less likely to get that jagged line of missing data) if you don't have the cameras going off simultaneously (which should also be easier to implement )

[djellison]

Now that's cunning - and even though the data would suggest otherwise - I'm still tempted to use a simultaneous release just because we then know we've got n 2 or 3 frame panoramas. What do your sims say for two cameras in portrait, two in landscape, three in portrait, three in landscape with say, 10% FOV overlap?

I've had another idea for a self monitoring camera which could be cool....got to wait till I have the gondola boxes and a few cheap digi cams

Doug

[jamescanvin]

Your wish is my command...

In each of these I've used the same orientations of the gondola when each picture is taken to make them somewhat comparable. In each case there are 15 images from each camera. Also included is the coverage after one shot from each camera and two percentages indicating the total coverage and the coverage in the lower hemisphere (as the upper one should be mostly black sky ). Of course this is very biased as a lot of pixels near nadir represent very little solid angle in this projection but hopefully it tells us something. The cameras are arranged so they have about the same amount of overlap between the images (5 degrees or so).

1) Similar to before two cameras, upper in landscape, lower in portrait and pointed down at 40 degrees. 61% 86%



2) Both cameras in portrait one pointed down at 45 degrees. 65% 91%



3) Both cameras in landscape one pointed down at 35 degrees. 54% 71%



Sims using three cameras to follow.

[JRehling]

[...]

[jamescanvin]

4) Three cameras all in landscape with elevations +15, -20 and -55 degrees. 76% 99%



5) Three cameras all in portrait, two side by side (35 degrees) with one underneath (-45 degrees) 72% 96%



So in conclusion, if we can stretch to three cameras I'd go for option 4 (even with just 10 images per camera I still get 94% coverage of the ground hemisphere in this simulation). This one also has the added benefit of being a bit Huygens like.

James

[ngunn]

Why not just have two photographers head to mountaintops, link up by cellphone and synchronized watches, and shoot photos of the same cloud formations at the same time? You could even do this without the mountains, but I think someplace like the Cascades of Oregon or Washington state would be ideal locations.

Venus Titan and Neptune, on the other hand would be less than ideal. Nobody was suggesting that you need balloons to study terrestrial cloudforms. Indeed a movie or sufficient still shots from any fast aircraft or satellite would achieve excellent results without the need for mountaineers. My idea was to use Earth's conveniently accessible and largely transparent atmosphere and Doug's simple-as-possible balloons to try out a technique that might prove practical and cost-effective in more awkward locations elsewhere in the solar system.

[djellison]

Well - I've just ordered three very VERY cheap 3 megapixel cameras. Cheap enough that I don't care if they get...

1. Broken by me stripping them out to work with a timer circuit
2. Frozen to death
3. Broken on landing via drowning, crushing etc
4. Lost for all eternity - last seen at 95,000ft over Norfolk.

And also - if they're any good at all - I''ll get another half dozen just so we've got 'stock' as it were. Once I know roughly how large their images are, I'll get SD cards to suit the requirements of >3 hrs at 20 second intervals.

For the price of my 400D (which isn't going within 10 miles of a polystyrene fish storage box hung under a giant condom full of helium some idiot from Leicester's going to let go) - I could by 24 of these 3 megapixel jobs. Once I have them (this weekend - I'm away giving a talk tomorrow) - I'll 'calibrate' them to find their actual FOV and work on some sort of internal framework (balsa and/or foam) to mount them at appropriate angles to one another in landscape (if the vertical FOV is >45 degrees) or portrait (if the vertical FOV is <45 degrees)

Before that - I want to figure out how to power all three from one big-ass central power supply, how long that will last, and if I can wire them up into one relay - or if I'll have to power three relays with the one timer circuit relay...to trigger them. Once I've got my mirrors - I'll be figuring out if CatCam can do the GMC campaign on its own - or if I want to tie that in with the same circuit (I think I do)

Meanwhile - got to convince the photographer that she wants to let catcam get trashed....could be difficult.

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[helvick]

Stunning work with those coverage sims James.

The coverage question and whether we should try for three cameras leads me back to some research that we need to close out on. We know that some of the mid range Digicams (Some of the Canon PowerShots (S3is, S5is , 570) and some Casios have an internal time-lapse\intervalometer mode that is hugely useful. What we really need is to find a camera that meets the following:

Must have features:
Lightweight: <200g ? If we want to fly three cameras then we really should be looking for <133g
Time-Lapse mode \ Intervalometer _or_ a lightweight trigger circuit
Capability to be powered by external DC source
Fully automatic exposure control (this is a given in a digicam)

Desirable Features
Low cost: The cameras are very likely to be consumables in this exercise so it would be smarter to select a cheap one.
Wide Angle.
High resolution
Good optics

Any other suggestions?

Doug - My Fujitsu Siemens Loox-T is not responding to intensive CPR so I've given it to someone better qualiied to try and recover it. In the meantime I'm trying to scam a replacement out of my various contacts. If all else fails I'll buy sufficient kit for the cause. I reckon I need about a week to get the code to send GPRS and SMS GPS coordinates working, fortunately I don't need a working GPS enabled device to develop and test that so we should have a high level of confidence in that system fairly soon even if I haven't nailed down the hardware.

[djellison]

Well - I think with these cheap cameras I've got coming - I'll tick the low-cost, wide angle boxes and bolt on a simple timer circuit. I need to establish what, if anything, is happening when the shutter is pressed ( is their current or voltage involved that might feed back from one camera to another etc - and does that even matter if they're all identical anyway )

With multiple cameras, the independent timer circuit is going to be a better bet than relying on the intervalometers of whatever type of camera we have - as I imagine they would drift out of sync with one another Power is still a 'hmm - what to do' issue - because the FM APRS Tx needs a power source as well - although it will happily run of a standalone 9V for a week or more. Amazingly - there are some C and D recharable cells that run to 5000Ahrs and 11000 Ahrs respectively. A pair of those for each camera would give us all the juice we would need (5000Ahrs is twice the capacity of an excellent AA)

I was worried about the cold on the GMC - but going for the most simple possible solution - http://www.bargainboards.co.uk/P/MyCoal-Fo...mers(1252).aspx - would make the problem go away entirely.

Once I have chute, box, cameras, FM APRS Tx, GPS - I can think about the mass budget and figure out how many Whr's we can get into it. If it's looking desperate then in order..things would get culled like this

3rd camera
2nd camera
GMC
IBS
Replace 1st camera with GMC fitted internally.

The bare minimum is one camera, and the FM APRS Tx & GPS. Then it's that + the IBS etc etc.

If your Loox is properly dead - and ignoring the beggars can't be choosers factor - it'd be brilliant if you could scrounge a similar model so that the dead one can become a mass model.

[ElkGroveDan]

If Helvick can't come up with another unit, I have a fully functioning Palm Treo 700 that I'd be willing to part with for this project.

[JRehling]

[...]

[djellison]

Someone else can drown their cameras intentionally - I'm only aiming to do it unintentionally There's a real engineering challenge in 'depth' for the payload protection - far more so than altititude - but the 'transport' would be so much easier ( a line, and some rope) interesting concept though.

[AndyG]

I was worried about the cold on the GMC - but going for the most simple possible solution - http://www.bargainboards.co.uk/P/MyCoal-Fo...mers(1252).aspx - would make the problem go away entirely.

Top marks for the heating option - though I would be somewhat wary of enclosing one of these in a thermally insulated sealed box. Could get toasty! Any idea of their wattage?

And I'm sold on the idea of flying a thermometer - Maplins do a 100k Bead Thermistor (for 90p!) that works down to -55C. But if a thermometer is to go - then a manometer's a must, too, in order to check altitude.

Andy

Edit: Rs Components offer a suitable manometer - but it's £40! Surely they can be found for less than that?

[djellison]

A 90p thermistor's great...BUT....you need something to read it, log it, and then spit it back out to you on the ground - it becomes a big problem.

There are commercially available stand alone thermometers that log - but they're not cheap. More sense for a first flight might be a simple standalone max/min system like this http://www.maplin.co.uk/Module.aspx?Module...er&doy=3m10 Something like that will also let me test the GMC sub-ass in the freezer with the lead hanging out.

We wont have a full trace- but we will have a record of the 'worst' conditions both internally and externally. For understanding the 'system' - that's a usefull point.

I want to pack this thing full of as many simple, stand alone, independent systems to get as much as we can, as easily as we can, as cheap as we can - to learn how it all works - so we can say "Yes - we know how to fly a balloon to >80,000 ft and get it back safely"

THEN....we can start thinking about some onboard intelligence that can measure and log...

Lat
Long
Alt
Pressure
Multiple temperatures ( internal battery - internal camera - external - external GMC )
Voltages
Acceleration in 3 axis
Orientation in 3 axis

PLUS - scientific study such as UV etc etc.

But that's a whole realm of 'how the hell....' beyond my knowledge - and I want to figure out how to fly a balloon and get it back before figuring out how to make it a genuine platform for investigation.