1. typically are fired during the final phase of selecting a propellant for use in a particular motor design. In some instances, they are scaled replicas of the full-scale motor design. This has been practiced in the des' n of extremely large solid propulsion systems.%) However, the small ballistic evaluation motor is more frequently of a simple design. Characteristically, these evaluation motors are similar t,o those described in Ref. 57 and 66 and comply to the rec mm ndation of the ICRPG Static Test Working Group.?577 The design should provide B neutral pressure-time .trace (withln 2 10%); a sharp tailoff <0.87 action time, and tail-off pressure integral < 5%action time pressure .integral; a gfain pyt-to-throat area. ratio, AF: 6;and a low length-to-diameter ratio, L D < 2, to minimize erosive burning influence. Burning duration should he short, 2 to 10 seconds, to minimize heat loss and nozzle erosion. Nosale throat insert material and size should be selected to minimize throat erosion and produce a chamber pressure that is withi 6 2 10%of. the full-scale motor operational value. Nozzle geometry is typically conical with a 2 0.5 exit cone half angle and dn expansion ratio slightly lesa than optimum. The lat 6er is to guarantee full flow attachment throughout motor equilibrium burning. To avoid unwanted mass flow contributions due to inerts, little or no liner should be used; therefore, specific impulse can be based on propellant charge weight. Consumed weight should be determined by pre- and post-firing motor weight measurements. A propellant weight of about 50 pounds has been found desirable' for the general small ballistic motor charge. This w i l l permit satisfactory scaling to a l l motor sizes. Howivver, for a full-scale motor of 30 inches in diameter or less, satisfactory scale-ups have been made from ballistic evaluation mo.tors w.ith a 5- to 10-pound propellant charge. Examples of ballistic evaluation motors that meet these eneral requirements are the AFRPL BATES motor(86) and the Rahm and Haas 6C5-11.4 motor,(13) respectively.