V. INSTRUMENTATION AND EXPERIMENT PHILOSOPHIES J. D. Shreve Presiding (A) Sampling the Upper Atmosphere for Particulate Matter M. Markels, Jr. Atlantic Research Corporation Introduction Sampling the upper atmosphere for particulate matter is necessary to predict accurately radioactive inventory in the atmosphere and its rate of descent or fallout. Currently, high-altitude balloons carrying a blower and filter unit can sample the upper atmosphere to about 100, 000 feet. But analyses of these samples, together with world-wide fallout studies, suggest that considerable radioactivity is present at altitudes above 100, 000 feet. Atlantic Research Corporation, under Contract AT (30-1)-2404, entitled, Sampling the Upper Atmosphere for Particulate Matter", has evaluated various particle-collection systems for sampling in the altitude range extending from 100, 000 to 200, 000 feet. Since a rocket appears to be the most practical vehicle for reaching these altitudes, the feasibility of the sampling method selected was determined on the basis of use with a rocket vehicle. To sample the required 1,000 std cu ft of air, supersonic impactors which use the velocity of the rocket vehicle for removing the particulate matter from the air are impractical because of the excessive drag imparted to the rocket. The low density of air above 100, 000 feet requires a long sampling time to avoid super- sonic flow and large pressure drop through any duct-type particle collector. to slow the fall of the particle collector. Therefore, a device must be added A second consideration resulting from the large sample size is the large amount of work which must be expended to move the air through the sampling device and to separate the air from its load of particulate matter. The cost and complexity of rocket vehicles capable of moving large payloads indicates the desirability of using as large a fraction as possible of the potential and kinetic energy of the rocket in the sampling operation. A rotorchute with impactor arrays can collect the required sample efficiently. device which operates like a gliding helicopter or Autogiro. to rotate the blades. A rotorchute is a bladed Energy from the vehicle descent provides the power The blade lift in turn slows the fall of the vehicle to descent rates only slightly faster than those of parachutes of the same over-all diameter. The energy which keeps the blades rotating can also be used to move impactors through the air which collect the particles much the same way dust collects on a fan blade. The large mean~free path of the air molecules at 100, 000 feet and above greatly increases the efficiency of impactor devices, and such a rotorchute and impactor system gives a simple method for processing large volumes of air. 101