BATES is an acronym for BAllistic Test and Evaluation System, which is a standardized system for measuring solid rocket propellant performance developed by the United States Air Force Research Laboratory in the early 1960s, used for almost forty years thereafter, and again beginning in 2010. According to this reference, a single propellant grain was used in the original AFRL BATES motor design. An AFRL BATES propellant grain is inhibited on the OD, burning only on the 2 outer ends and the central bore, and is dimensioned so the burning area does not change significantly (< 3% in the original BATES motor) through the burn, generating a flat-topped thrust curve (neutral burn) to minimize propellant characterization costs and simplify the data analysis.
In modern usage, BATES often refers to a type of solid-fuel rocket motor grain geometry. A BATES grain consists of two or more cylindrical grain segments with the outer surface inhibited, but free to burn both on the segment ends and the cylindrical core. Such grains can be configured to achieve a desired thrust-time profile while maintaining an acceptable center of gravity.