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This paper describes a navigation system incorporating inertial and two-antenna carrier phase differential global positioning system (GPS) measurements. The major objective is to demonstrate full attitude determination even for a nonaccelerating vehicle. The motivating application for this project is vehicle control. Therefore, the system is designed to operate reliably whether or not GPS measurements are available. The navigation system estimates vehicle position, velocity, acceleration, attitude, and angular rates at 150 Hz with accuracy (standard deviation) of 1.5 cm, 0.8 cm/s, 2.2 cm/s/s, 0.03 deg (pitch and roll), 0.1 deg (yaw), and 0.1 deg/s using a 1.01 m baseline between antennas. The navigation state vector is processed to produce a control state vector at 30 Hz. The control demonstrations involve basic trajectory following as well as trajectory relative maneuvering (i.e., tracking sinusoidal perturbations and performing lane changes). During experimental testing, a magnetic system was available to provide a ground truth reference. The demonstrated accuracy is sufficient for control of vehicles in an automated highway system. Other possible applications include precision farming, aircraft and satellite control, and control or guidance of automated mining or highway maintenance vehicles.