Advanced Inertial Reference Sphere
The Advanced Inertial Reference Sphere, or AIRS, is a highly accurate inertial guidance system designed for use in the LGM-118A Peacekeeper ICBM and later the Minuteman III.
Details
AIRS is a fluid stabilized system, as opposed to one using gimbals. It consists of a beryllium sphere floating in fluid. This not only eliminates the problem of gimbal lock, but also makes it extremely accurate, accurate enough so any further improvement would give a negligible benefit to the missile's CEP. However, it is extremely expensive.
Usage
The AIRS was originally developed for the LGM-118A Peacekeeper. The first AIRS's were manufactured by Northrop.