of events performed to obtain a sample of particulate matter from the atmosphere. According to Dr, Machta's data presented yesterday, our sampled volume will be sufficiently high that we could use a portion of the flow through passages in each of several altitude zones. To ensure a minimum number of shots to develop such a sampler, reliability of the components and opera~ tion of the complete system should be tested in ground facilities. existing 26-foot vacuum sphere at Sandia. sampler components. Figure 2 shows planned modifications to an The sphere is intended for use primarily to test mechanically all Specifically, rotor hardware strength and thrust requirements for given rotational speeds at varying altitudes, together with flutter characteristics, will be investigated. In the latter develop- mental stages, such items as the deployment, retraction, and sealing of the sectional rotor blades will be tested. Finally, tests may be made in the vacuum sphere to determine flow patterns through and around the sampling rotors, and to collect samples of particulate matter that have been injected into the sphere. altitudes up to 150,000 feet can be simulated in this sphere with existing pumping facilities. Density The rotor blades would house flow-through passages that contain filter material for the diffusive collection of debris present in the sampled air. For a given expected particle-size distribution, there should be some filter material with a specific porosity that will most efficiently obtain a debris sample. Considerable filter testing must therefore be done to ensure selection of optimum filter material for use inthe sampler. now being fabricated. Figure 3 shows this test equipment. A filter test rig for this type testing is Mr. Rigali will present the details of the equipment in the final portion of this presentation, Dr, Banister from our Physical Sciences Research Department will next present the theory of diffusive collection, Theory of Diffusive Collection (J. R. Banister) Mr. Matejka has just finished describing a possible rocket system which samples by means of a rocketimpelled system that sweeps up debris. use with such a vehicle. I would now like to talk about the possible filtering media one could It might be worth mentioning that our thinking in this regard has comeout of the design calculations we did for the impactor sampling system developed for the early sampling of the debris of Teak and Orange shots of Operation Hardtack. and Sandia Report, SC-4172(TR). 2 These calculations are described in detail in wT-16014 Two important principles emerge from these calculations, For the Teak shot, we were using an impactor arrangement of canted parallel plates which were separated by one centimeter. We found that this impactor arrangement was theoretically extremely effective at low air densities. In fact, at 250 kilofeet, the collection by impaction was essentially perfect for particles down to 10°" cm in diameter, when the rocket speed was about 2000 fps. A significant sidelight that came out of the calculations was that as the arrangement began to fail as an impactor, it became effective as a diffusive collector. The Brownian movement of the near molecules was sufficiently high that the particles were collected by diffusing to the walls of the impactor while they were flowing through it. The consequence was that, although on an impactor basis, one would predict that the collection efficiency would vanish as the particle diameter approached zero, the over-all performance remained satisfactory down to molecular sizes, 39