Rocket trajectory correction using strap-on GPS guided thrusters

Oerlikon Contraves GmbH and Rheinmetall W&M GmbH are developing a system known as COntraves REferenced Correction for Trajectories (CORECT) to determine a rocket's trajectory using GPS data and then to correct the trajectory using a system of strap-on thrusters. Rockwell Collins is providing the GPS receivers and the integration support. This system uses multiple GPS antennas mounted at regular intervals around a high speed rotating rocket. The antenna signals are then routed through a combiner so that more or less continuous GPS signals are provided to a Rockwell GPS Embedded Module (GEM) III receiver. An integration computer compares precomputed rocket trajectory data with the actual GPS position data. The computer uses up to 32 thrusters mounted around the rocket to apply real time corrections to the rocket's trajectory. Trajectory aiding is provided to the GPS receiver to aid in reacquisition after launch and to improve tracking performance. The other significant portion of this navigation system is the use of a magnetic sensor to measure roll angle based on the rocket's attitude with respect to the Earth's magnetic field. The initial probability estimates for CORECT indicate a great deal of promise for improvement of circular error probable (CEP) at the target. Tests of this system have been conducted using a GPS simulator and a rotating antenna fixture to simulate the rotation of the rocket. Individual tests of the thrusters have also been performed. In June of 1997, a successful live firing of a missile using CORECT was performed through which a significant end-game improvement (400 m at 20 km) was demonstrated. This program shows innovation because it provides a relatively easy way to add GPS guidance to an existing rocker. The next phase of this program is the development of the final modular system.