(F) Some Recent Developments in Balloon- Borne Stratospheric Sampling Systems R. C. Wood General Millis, Inc. Introduction As the title implies, this paper contains a short discussion of balloon-borne stratospheric sampling systems. More specifically, it describes equipment and techniques developed at General Mills, Inc. in con- nection with research programs conducted under the sponsorship of the United States Atomic Energy Commission, the Air Force, and other agencies. superficially. In this outline, three general areas are covered, some perhaps They include: (1) Some brief facts concerning balloons in general, load carrying capacity, altitude capability and cost of research flights, (2) A description of present sampling methods employed by this laboratory with a few recently added improvements, and (3) Some promising new approaches toward an increased sampling capability at higher altitudes. Some Balloon Facts In order to convey some idea of the variety of balloon designs available for stratospheric research flights, we may refer to Figure 1 in which each point represents a specific polyethylene balloon designed to carry a given load to a given altitude. The curved lines superimposed merely serve to classify these designs roughly according to size in terms of millions of cubic feet (fully expanded at altitude). At present, a' 200-pound load can be lifted to 140, 000 feet using an eight million cubic foot balloon costing approximately $8000. Not shown on Figure 1 is an existing fourteen million cubic foot design which can lift 200 pounds to 150, 000 feet. Present research balloon flights at Minneapolis operating within the altitude range of 50 to 90 thousand feet carry, routinely, loads averaging 500 to 1000 pounds. ranges between $1000 to $2500. The average cost of balloons used in these flights An average flight operation costs $7000 to $10,000, including equipment pre- paration, launch and recovery. Present Sampling Methods On research flights performed at Minneapolis, two basic methods have been employed for particulate sampling: (1) Cascade impactors which sample twenty-two ambient cubic feet per minute, and (2) Filter samplers which operate at rates in excess of 500 cubic feet per minute, 149