INSENSITIVE MUNITIONS PROPULSION PROGRESS

Abstract

Increasing interest in the application of thrust-managed, solid-propellant rocket motors for future missiles has prompted a desire to learn how these motors might react to the stimuli involved in the MIL-STD 2105B1 insensitive munitions (IM) hazards tests. An opportunity became available for the Insensitive Munitions Advanced Development (IMAD) Propulsion Project to obtain four experimental, dual-pulse (two chamber) rocket motors; these motors were subjected to the fast cookoff, slow cookoff, bullet impact, and fragment impact IM hazards tests. These motors had steel cases with a bulkhead separating one pulse from the other. The propellant for each pulse grain was a nitrate-ester-plasticized, reduced-smoke, hydroxyl-terminated polyether (HTPE) propellant. Reactions in the IM hazards tests were classified as follows: fast cookoff, deflagration (fail); slow cookoff, explosion (fail); bullet impact, burn (pass); and fragment impact, explosion (fail). In the cookoff tests, the aft pulse (pulse 1) reacted first followed by the forward pulse (pulse 2). Delay times between the reaction of pulse 1 and pulse 2 were 5 seconds for the fast cookoff and 45 seconds for the slow cookoff tests. It was unexpected when pulse 1 reacted first, because this pulse's chamber consisted of thicker insulation. In the impact tests, the projectiles and fragments were aimed at the pulse 2 chamber resulting in the reaction of this pulse with no accompanying reaction from pulse 1. The implication of these results is that separate chamber, pulsed motors containing a relatively insensitive propellant such as the HTPE propellant will probably provide less collateral damage than motors in which an equivalent amount of propellant is contained in one chamber.