A GNSS (Global Navigation Satellite System) is a system that will use either or both NAVSTAR and GLONASS to provide positioning, along with other components to improve accuracy and provide fast warning of problems. No GNSS systems are currently operational.

A GNSS must include: (1) Real time navigation information: the ability to generate real-time navigation information fast enough for safe navigation. Both the NAVSTAR and GLONASS systems provide near-instantaneous positions. (2) Autonomous integrity checking: a way for the user to determine the accuracy of the navigation solution in a timely fashion. Generally this problem is solved by having the receiver view a large enough number of satellites that it can calculate several sets of redundant positions, comparing them against each other. Bad solutions can be detected and thrown out. At this time, neither the NAVSTAR or GLONASS systems have enough satellites to do this. The only way to do it is to use both NAVSTAR and GLONASS satellites at the same time. (3) Accuracy sufficient for safe navigation. The US Department of Transportation has determined that the most stringent requirements for aircraft landing are 4.1 meter horizontal accuracy and 0.6 m vertical accuracy. There is no way for either NAVSTAR or GLONASS to provide this accuracy without external aids. A GNSS using NAVSTAR and GLONASS would be the solution.