A position determining system that includes a spherical inertial sensor assembly, at least one position determining device and a processor is provided. The spherical inertial sensor assembly has a surface with a reference pattern. Each position determining device includes a focal plane configured to record images of the reference pattern and star images. The processor is configured to determine the angular position of the spherical inertial sensor assembly via recorded images of the reference pattern and correlate the determined angular position based on the star images.