# What altitude limits exist for the GPS receivers on Altus Metrum products?

The U-blox parts we use perform well in airborne mode, and are the gold 
standard for hobby rockets.  However, series 8 and below reportedly stop 
reporting above 50km altitude, and series 10 stops reporting above 
80km.  We do not have flight data from anyone who's gone that high to confirm
or deny this, though others report confirming it with GNSS simulation systems.