Spacecraft Guidance, Navigation and Control Systems

Abstract

AbstractThe difficulties in maneuvering a vehicle through space are not intuitively obvious to someone who has not been involved in the field.The finite limits of electrical energy, thrust, and propellant on a vehicle are the driving forces that demand efficient and accurate equipment to perform the functions of steering and navigation and keep the vehicle attitude stabilized. Added to these restrictions are the needs for minimum volume and mass. An intricate system results that is extremely difficult to design, construct, and test and usually is one of the most expensive on the vehicle.Guidanceis the actual steering of the vehicle as it travels through space. Guidance commands may originate from a crew onboard, from an onboard computer, or from external sources via radio commands. In addition, if the thrust of a space vehicle is variable and controllable, the command for modulating the thrust is usually a guidance function.Navigationis the measurement of the location of the vehicle in space and plotting the course of the vehicle. Navigational fixes may come from onboard human sightings using telescopes and sextants, from automatic onboard star or horizon sensors, or from radio/radar tracking equipment on the ground.Controlrefers to the spatial alignment and stabilization of the vehicle while the guidance and navigation functions are being performed, and includes onboard processing and routing of commands to the devices (typically thrusters, reaction wheels, control moment gyroscopes, or aerodynamic surfaces), termedeffectors, that produce reactive forces on the vehicle.The combination of these three functions into one system results in theintegrated guidance, navigation, and control system, or simply the GN&C system. This article discusses each of these systems. It also gives information on permutation, integration verification, and the flight computer.