(C) A Cryogenic Air-Sampling Rocket D. F. Burcham* and A. M. Haire Aerolab Development Company H. BE. Karig National Engineering Science Company The collection of particulate matter from the upper atmosphere above the altitudes where balloons can be used can be accomplished by several methods, the most common of which is impaction. ticles approach molecular dimensions, these methods becomeless efficient. However, as the par- The requirement for the system under discussion was collection of rhodium-102 particles at altitudes above 40 kilometers. The project is sponsored by the Cambridge Research Laboratories. The most feasible collection method under these circumstances is one which captures all the air and particulate matter within a swept volume. No attempt to differentiate between molecules of air and rhodium is made during the sampling period, such identification being reserved for subsequent laboratory analyses. This necessarily implies that the volume of air captured must be reduced to reasonable dimensions and stored pending laboratory analyses of the sample. ling rocket. The design to be described is of a cryogenically cooled air sam- The rocket consists basically of a heat exchanger with liquid hydrogen as the coolant. Air enter- ing the heat exchanger is cooled and either condensed or solidified depending upon whether the recovery pressure is greater or less than the triple point pressure. in this sampling system will be presented, The most important theoretical and practical considerations Details of the theoretical analysis are by Karig, Gagnon, and Bass, To assure that the sample is a representative one, the free stream capture area must be constant throughout the sampling regime. By providing a normal shockat the inlet, the capture area remains equal to the inlet area, If the shock becomes detached, air spillage from the inlet occurs, which results in a reduction of capture area. As air is spilled around the inlet, entrained particles are deflected such that there is a nonrepresentative concentration of particles in the captured sample. The shock may become detached through perturbation of either the external or internal flow. at supersonic speeds the bow shock wave will precede the body of the payload, For example, The inlet must extend sufficiently forward of the main vehicle to avoid interaction between the standing bow shock and the inlet flow. Internally, shock detachment may occur if the back pressure becomes too high. mechanisms by which the maximum allowable back pressure can be exceeded. flow to attain sonic velocities somewhere downstream of the normal shock. There are two possible Viscous forces may cause the Therefore, all flow passages, in- cluding the heat exchanger tubes, must be designed to minimize the effects of viscous forces. * Sneaker presenting the paper. In order to