Chapter 2 PROCEDURE» ’ . 2.1 SHOT PARTICIPATION The project initially planned to participate in Shot Koa, a megaton-range land-surface burst, and Shot Walnut, a megaton-range water-surface burst. Because of apparent contamination of the Koa cloud samples by debris from Shot Fir, participation was later extended to include Shot Oak, a high-yleid water-land burst fired over the lagoon reef. Device information is given in Table 2.1. The project rockets participated during Shots Koa and Walnut and were also fired during Cactus and Yellowwood for system check and nose cone recovery practice. Aircraft were flown during Koa, Walnut, and Oak. 2.2 INSTRUMENTATION The instrumentation for this project fell into two general classes: rocketborne and aircraftborne cloud samplers. Two types of aircraft, B-57D’s and WB-50’s, were used. 2.2.1 Rocketborne Cloud Sampler. The rocket, a 20-foot unit, consisted of an air-sampling nose section, a two-stage propulsion unit and various items of auxillary equipment (Reference 69). Figure 2.1 shows a complete rocket on a launcher. Part A is the primary motor, Part B the sustainer motor, Part C the parachute compartment, Part D the electronics compartment, and Part E the air~sampling nose section. The air-sampling diffuser of the nose section was 36 inches long, as measured from the intake orifice to the filter (Figure 2.2). An additional 32 inches of length behind the filter was occupied by exhaust ports and auxiliary equipment. The extreme forward part of the rocket was a conical section 5 inches long, which sealed the intake orifice prior to the time when Sampling was begun. The orifice of the diffuser was 2 inches in diameter, and thefilter was 8, inches in diameter. An expansion from 2 to 8, inches in diameter in a length of 36 inches gave an expansion angle of 10°, the maximum at which the flow would not separate from the diffuser walls. The filter was an 8-inch circle of matted cellulose fiber coated with stearic acid to help retain the particles. It was supported by a wire retaining screen. The inside wail of the diffuser was in the form of a revolved segmentof a circle 250 inches in radius and was parallel to the axis of the rocket at the orifice. Particles entering the sampling section were decelerated from about twice the sonic velocity to subsonic by passage through a shock front that formed nearthe throat of the diffuser. Fol-_ lowing this, they were subjected to a force field that caused the smaller particles to be impelled toward peripheral areas of the collecting filter to a greater extent than the larger particles. The diffuser was designed to effect a resolution of particles having average settling ratee greater or less than 3 in/sec in the normal atmosphere (Reference 69). A light akin was wrapped around the outside of the diffuser to fair up the external shape of the nose cone. The propulsion section contained primary and sustainer motors, both of which were solidfuel units about 6 inches in diameter with burning times of 6 seconds. The sustainer motor was ignited shortly before the start of sampling and provided sufficient thrust to maintain the rocket speed at about Mach 2 during passage through the cloud. 22