[time-nuts] GPS Arctic graphs
leo at leobodnar.com
Sun Aug 27 15:18:24 EDT 2017
Perhaps, completely unrelated and useless information - I had a small balloon that flew about 9km off the North Pole at altitude of around 13km while reporting its position derived from GPS.
Telemetry included time, date, coordinates, altitude, number of GPS satellites, onboard temperature, battery and solar panel voltages.
The raw data is still available here http://leobodnar.com/balloons/B-64/B-64-telemetry.csv
What can I say which is of interest? It was very cold, down to -60C at night, GPS works everywhere, number of useful satellites increased as you move towards the North and the Sun indeed does not set on the North Pole during summer (but stays very low to be useful.)
I have used Ublox MAX-8Q for navigation. It was able to cope with low temperatures - way below its specified limit but it really did not like sharp temperature changes, e.g. during sunset. Which is expected.
When the Sun sets temperature changes by 10-30C down within few minutes, below -45C TCXO finds itslef way way outside its correction zone and starts drifting a lot (I suspect even worse than just XO would), tracking engine gives up and falls back into acquisition mode and it really drains the batteries. I had a tiny local heater for TCXO but can't say how effective it was - probably not very. For power management reasons I have used power saving mode so acquisition fall-backs were not welcome. I was also not able to find a way of deferring Ublox download of ephemeris during the night, where the power is extraordinarily precious.
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