Global Positioning System (GPS) receivers provide accurate position and velocity measurements. Aerospace is investigating how these measurements can be used to complement the measurements made by an inertial measurement unit (IMU).
Both GPS and IMU systems have instrument and environmental error sources that contribute to navigation errors; however, because the two systems use completely different methods to navigate (lines of sight versus dead reckoning), their error behaviors differ. For example, IMU navigation error grows with time, but GPS navigation errors do not. An IMU is more accurate than GPS over short periods, but as flight time increases, GPS becomes more accurate. Launch vehicle position is currently computed using the IMU alone; but by incorporating GPS receivers on the launch vehicle, a more accurate and reliable measurement of position can be obtained that is less prone to error growth.
Aerospace is supporting efforts to incorporate stand-alone GPS systems on launch vehicles for range safety. This GPS data will complement the current telemetry and radar tracking, but will not be available to the flight software.