Inertial guidance, navigation, and control systems

T Department of Defense (DoD) and NASA invested more than 1.5 billions of dollars in guidance, control, and navigation during the past fiscal year. The technology represented by such a funding level (which does not even include other major customers such as the Federal Aviation Agency) is a far cry from the fixed rifle sight, the sextant, the eyeball, and "chewing gum on the windshield." A few clarifying definitions should be stated at the outset. A system that simply indicates the position and velocity of a vehicle is a navigation system. If a navigation system is placed in a closed loop with a vehicle's controls via a guidance computer in order to control the position and velocity of the vehicle, a guidance (and control) system results (Fig. I). The related processes of guidance and control may be distinguished as follows: Guidance is the process of continually correcting the velocity vector of the center of mass of the vehicle, so that the vehicle will reach a specified point in space and time. Control is achieved by movements about the center of mass to adjust the lift and drag forces on the vehicle. (Control of engine thrust may or may not be involved in these processes.) Three commonly used classes of guidance and navigation systems are 1) inertial systems, "without the use of any radiation, either natural or man-made"; 2) radiation systems (that rely upon optical, radio, radar, or infrared data, and that include command systems and homing systems); and 3) externally aided inertial systems (combinations of types 1 and 2). The relative emphasis being placed on inertial techniques in the United States is indicated by a relative breakdown of DoD and NASA funds for guidance systems and components for fiscal year 1964 (Fig. 2). The DoD and NASA both spent about 50% of their research and development (R&D) money and 80% of their production funds (procurement for operational systems) on inertial systems. (The marked difference between relative R&D and production allocations is due to the high unit production costs of inertial systems relative