Gang,

I haven't tried in a while, but does anyone use pressure sensors with much success in HABs?  The reason I ask is that I have a pile of BMPxxx sensors and it would be no big deal to add them to a data logger, or other control systems that are altitude oriented.  I tried one years ago, but the formulas I had for converting pressure to altitude were generating wildly different results from the GPS. I just punted at the time.  I've got a bit of renewed interest, now, in having non-GPS oriented ways to test altitude.  It seems that using pressure could be a lot more reliable than hoping I get and maintain a GPS lock, especially if I have other RF activity going on on the payload.

Thoughts?
Mike / KD2EAT

Hi Mike,
We fly a baro as a backup for the GPS. We use a MS5611 because it is rated to 11 mbar, or around 100K'.  It's been quite a while, but if I remember right, there were 2-3 calculations based on temperature of the sensor to get from the raw value to mb.  Then there were another 2-3 calculations to get from mb to altitude based on the pressure.  In the end, we got pretty close.  This is a slide that I presented at the GPSL in Granbury TX.  This only goes up to 75K feet.  As it goes up, it gets progressively worse.  If I remember right, it is about 5K' difference at 100K'. Initially, we collected all the data from the sensor, then did the math on the ground. It took a few flights to get it tweaked in.  We don't correct for baro setting before the flight. That only seems to affect it by +-200'.  The goal was to get a good guess of the altitude as a backup so it didn't need to be spot-on.