Guidance, Navigation & Control
The GN&C subsystem handles the relative localization, attitude control, and non- scientific, non-thermal sensor hardware for the satellite. Attitude means the three- dimensional orientation of a vehicle with respect to a specified reference frame, attitude determination is the process of combining available sensor inputs with knowledge of the spacecraft dynamics to provide an accurate and unique solution to for the attitude state as a function of time, and attitude control is the combination of the prediction of and reaction to a vehicle’s rotational dynamics. For Low Earth Orbit (LEO) satellites, GN&C is often referred to as the Attitude Determination and Control Subsystem (ADCS, or ADACS). Because Commercial Off the Shelf (COTS) options for ADCS units exist that also provide GPS connectivity for position and velocity state vector determination and propagation over time, GN&C is a more broadly applicable subsystem name. Attitude sensors commonly include star trackers, sun sensors, horizon sensors, magnetometers, and inertial measurement units, while attitude control components include reaction wheels, torque rods (magnetorquers), Reaction Control Systems using propulsion, and propulsion units with Thrust Vector Control.
Wertz, James R, David F. Everett, and Jeffery J. Puschell. Space Mission Engineering: The New Smad. Hawthorne, CA: Microcosm Press, 2011. Print.
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