Hello. I am trying to find a suitable and obtainable pressure sensor to find the height of a high altitude balloon. I'm new to the Arduino community and am finding it difficult to find a sensor that will measure the height/pressure at 30 kilometres or higher up.
Thank You,
Edit: the pressure at 30km is around 0.01 bars or 10mbar
What is the air pressure at that height?
There are several sensors that can go pretty low, such as the MS5806-02BA (most accurate from 300 mbar but can go as low as 10 mbar).
Thanks for your response, the pressure at 30km would be around 0.01 bars. I guess I should have mentioned this earlier.
the MS5806-02BA sensor looks really promising, do you recommend any websites to purchase this sensor? I live in India.
Thank you, user @wvmarle
0.01 bar - that's 10 mbar - right at the edge of what it can do. I don't know of other sensors (including in the MS family) that go even lower. Maybe you should add a GPS receiver, that also gives you the height, maybe more accurate at that height as the sensor is rated at +/- 2.5 mbar or so absolute error which translates to 25% error at those pressures.
Another wild idea: take a differential, uncompensated pressure sensor such as the MPX2053DP, and seal up one of the openings (very tightly - you don't want air to escape and you're dealing with nearly 1 bar up there!). This way you basically use your local atmospheric pressure as reference. That one is rated to 5 bar difference, I don't know if it matters if the low end goes to vacuum. No idea if this works, just an idea.
No idea what would be a good site to order stuff from in India. Hopefully others can contribute on that part.
(commercial)GPS receivers don't work above 18,000m so I won't be able to use that.
I'll be considering the usage of the MPX2053DP sensor, but I too do not know if it will work or not.
I'm actually even considering using an analogue barometer and placing it in front of a camera haha.
Could you use the diameter of the balloon as an indication of air pressure?
@AWOL
That's really clever. I might be able to do that. The balloon is almost spherical and I could use the diameter of the balloon to calculate the volume of the balloon. Using the volume calculated and Boyles law (pressure is inversely proportional to volume), I could deduce the pressure at a certain height.
However this depends on if I'll be able to measure the diameter of the balloon, and it also depends on the balloon staying spherical. I expect the balloon to lose its spherical shape over time due to the payload that's attached on the bottom.
You will also have to compensate for the force to stretch the rubber material, which is pretty linear but at greater altitudes will not be linear any more as you reach the limit of how much it can stretch. So I don't think this is practical - and no idea how you could go about measuring the size of the balloon from a probe that's hanging under it.
For the GPS limit: that 19 km not a technical limit, it's a software limit. See here. You'll most definitely be going slower than the 1,200 mph, so there should be devices out there that may work for you. Do some shopping around, read reviews, ask friends that are doing the same.
Ah, thank you! that'll work then
I think actually already found one,
This looks pretty promising.
Thanks again @wvmarle !
Indeed, looks promising. Good luck with your project!
Do find a way for the balloon to call home with its GPS coordinates, makes it a lot easier to recover your stuff 
Thank you
I will probably use a GSM tracker or two to locate the payload.
good heat insulation is critical. The battery (for logging) should be kept above freezing temp.