Question

Why are there altitude and velocity limits for GPS equipment?

Answer

The reason there are limits for the altitude and velocity are due to US Department of Commerce CoCom GPS Tracking Limit regulations.

The U.S. Department of Commerce requires that all exportable GPS products contain performance limitations so that they cannot be used in a manner that could threaten the security of the United States. (For example Ballistic Missile Development).

In GPS technology, the phrasing “COCOM Limits” is also used to refer to a limit placed to GPS tracking devices that should disable tracking when the device realizes itself to be moving faster than 1,000 knots (1,900 km/h; 1,200 mph) at an altitude higher than 60,000 feet (18,000 m). This was intended to avoid the use of GPS in intercontinental ballistic missile-like applications. Some manufacturers apply this limit literally (disable when both limits are reached), other manufacturers disable tracking when a single limit is reached.
 
GPS Receivers will be affected by these limits unless specially enabled to exceed the limits.
Immediate access to satellite measurements and navigation results is disabled when the receiver’s velocity is computed to be greater than 1000 knots, or its altitude is computed to be above 18,000 meters. The receiver continuously resets until the COCOM situation is cleared.
 
In the latter case, this causes some GPS devices to refuse to operate in very high altitude balloons.
 
The Spectracom GSG GNSS Simulator has an option to allow it to exceed these limits. This option is available on the GSG-5 or GSG-6 series as Option-HV. Please note this option has strict export and usage restrictions. The Option –HV also requires the 16 Channel option be installed.