A water analogy technique was used in this investigation of the flow field in the pulse I motor of a two-pulse solid rocket motor. A full scale model of clear acrylic material was constructed to allow direct visual access of the flow field. The experiment, which was conducted with one of the VPI water analogy rigs, simulated the flow in the spent pulse I motor chamber after the pulse Il motor would have been ignited. The relations between the pattern and angle of the throughflow holes on the bulkhead--which separates the two motor chambers--and the downstream flow pattern in the pulse I chamber were assessed by changing the bulkhead model configuration for each test. Video records of the flow pattern were obtained through flow visualization tests, which used either fluorescein dye or air bubbles as the tracer. Also, hot water tests with thermocouple measurements were conducted as a means of investigating the rate of mixing of the propellent from the pulse Il motor with the gases in the pulse I motor chamber, as well as the migration of the pulse Il propellent along the wall of the pulse I motor casing. The test data show a clear relation between the hole arrangement on the bulkhead and the ensuing downstream flow pattern, as well as the rate of mixing along the wall of the pulse I motor casing. Consequently, the results provide directions for improving the performance of heat transfer insulation material on the wall of the pulse I motor through a prudent choice of the hole arrangement on the bulkhead. / Master of Science