Solving for the weight of air sampled between a given altitude and 100, 000 feet gives 1 -H/17, 120 W(100, 000) = 75,000 335 -e (4) This relationship is plotted in Figure 4 as the constant tip-speed curve. As can be seen from Figure 4, the weight of air sampled in dropping from 200, 000 to 100, 000 feet is over 200 pounds for the constant tip-speed design which is equivalent to over 2,000 std cu ft of air at a sampling efficiency better than 80 percent. If the optimum impactor size is used from Figure 3 for altitude increments of interest, a considerable increase in sample size can be realized in the higher altitudes. mental sample weights are shown in Figure 4. The calculated incre- These weights of air sampled are indicative of what is possible, but do not include refinements for such effects as slip flow. In order to achieve the sample size calculated, especially in the 200, 000 to 300, 000 feet increment, some redesign of the rotorchute and impactor system would be required. In order to obtain the low wing loading and large impactor size needed special techniques, such as inflatable structures, would probably be required. The rotorchute sample sizes shown are ten times as great as the best that have been calculated for any other system with this payload weight. Considerable thought was given to the problem of high altitude aerodynamics of this device. mental work has been done on the aerodynamics of rotorchutes above 100,000 feet. Little experi- However, present theory indicates that while the rate of descent may be somewhat greater than indicated by the calculations, the device should operate satisfactorily. entry vehicles.” There has been considerable interest lately in the use of rotorchutes to slow re- This is a definite indication that satisfactory aerodynamic capabilities in the altitude range above 100, 000 feet can be achieved. Since there will not be any serious aerodynamic heating problems with respect to the impactor surfaces, strippable coatings or double-surface pressure-sensitive films can be used for sample collection at the discretion of the experimenter. Since such coatings or films are made from organic materials the background radiation from an unexposed surface would be small. The total area for impaction is quite small, 53 to 70 sq in, in the example, depending upon ry: a concentrated sample for counting can be achieved. Therefore, The coating can be stripped off and packaged in the field or the entire impactor assembly can be shipped to the counting laboratory for examination. The sampling system described will weigh about 40 pounds, including the rotor blades, impactors, hub, controllers, and telemetering. Atlantic Research Corporation. This collection system would be compatible with the Arcon rocket developed by This vehicle will lift a 40-pound payload to over 300,000 feet, but the aero- dynamic drag associated with the folded fins would probably bring the apogee to the maximum desired altitude of 200,000 feet. The total length of the rocket is about 13 feet which is quite close to the 14-foot blades assumnedin the calculation. The major cost for each firing would be the cost of the nonreuseable rocket motor, which sells for about 35,000 per round depending, of course, on quantity purchased. The entire payload assembly will probably cost somewhat more than the rocket motor but the fact that it may be made fully recoverable should make the cost of this component under 52,000 per test. 108 A somewhat larger rocket capable o: sending a 50-pound payload to 100