How to determine altitude where altimeters fail?

[Lucas Thelen]

So above the majority of the atmosphere, altimeters that use barometric pressure fail, so barring regulation GPS modules, that generally don't work on extremely high altitude flights, how do you determine the altitude of your flights?

 

[jderimig]

Up to 50km, gps. Above 50km, space rated gps.

 

[Wallace]

$$$

 

[Lucas Thelen]

Up to 50km, gps. Above 50km, space rated gps.

Thanks, and apparently.

 

[Wallace]

If I remember correctly, if, it's around 5K over the hardware cost to "attempt" to have a gps chip unlocked for anything over 60,000'. Not me, just life...

 

[Lucas Thelen]

If I remember correctly, if, it's around 5K over the hardware cost to "attempt" to have a gps chip unlocked for anything over 60,000'. Not me, just life...

Though I have found an interesting way to pick up GPS satellite signals using an SDR radio. Maybe there's a way to decode it with python...

 

[jderimig]

Yes, you can fly an sdr and record the GPS carrier. You need a large flash drive. Then extract the position data on a PC running gnss-sdr.

 

[JimJarvis50]

It won't be long before moderately priced gps units are available that don't lock up at 50K meters.

Jim

 

[jderimig]

It won't be long before moderately priced gps units are available that don't lock up at 50K meters.

Jim

Yup. ;-)

 

[Wallace]

Yup. ;-)

Ya'll seem to know something we don't. Hmm..

 

[Lucas Thelen]

Ya'll seem to know something we don't. Hmm..

Intreaguing

 

[Lucas Thelen]

Yes, you can fly an sdr and record the GPS carrier. You need a large flash drive. Then extract the position data on a PC running gnss-sdr.

If one can pump the data into a Raspberry Pi, you could probably calculate the data live, if you keep updates to once a second or so. I know GNSS-SDR can be compiled to embedded platforms.

 

[jderimig]

If one can pump the data into a Raspberry Pi, you could probably calculate the data live, if you keep updates to once a second or so. I know GNSS-SDR can be compiled to embedded platforms.

Conceivably yes but there is alot of optimization tuning required to get gnss-sdr to work. Its one thing to acquire and lock a stationary gps receiver and another to do the same with a moving receiver and antenna.

If you have a recorded signal you can try all the options on the ground until you find a way to decode the signal.

 

[DaveW6DPS]

If I remember correctly, if, it's around 5K over the hardware cost to "attempt" to have a gps chip unlocked for anything over 60,000'. Not me, just life...

The "HA" here says 84 km. >270,000 feet, for $74. I have seen these fly in high altitude balloons over 120,000 feet.

 

[DaveW6DPS]

Though I have found an interesting way to pick up GPS satellite signals using an SDR radio. Maybe there's a way to decode it with python...

It is not a matter of just "decoding" the signal. You need a GPS receiver picking up multiple satellites and an algorithm to calculate time and position. There are a number of high altitude GPS receivers used in high altitude balloons that work well.