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 Northrup. After the US phased out the Peacekeeper in accordance with the START II, it was decided to retrofit the remaining fleet of Minuteman IIIs with AIRS. As a result, 652 additional units were purchased, and built by Rockwell.