The Roswell Report: Fact vs. Fiction in the New Mexico Desert

various cluster arrangements. None of these have been too satisfactory but further investigation will be made in the field of shrouded or coated films.

## B. Altitude Controls

Given a balloon capable of carrying the instruments to a desired altitude (the theory and computations involved are discussed in Section 3), there remains the problem of maintaining the cell at a constant level. The buoyancy of a gas-filled cell will decrease as the gas leaks or diffuses through the balloon wall. To hold an absolutely constant altitude, the volume of lifting gas entrapped must be maintained in an atmosphere of unvarying horizontal density, with no change in the total weight supported by the balloon and with no fluctuations of the temperature of the gas with respect to the air. The best approximation to these conditions may possibly be achieved through the use of liquified hydrogen, which would be permitted to evaporate at a rate in excess of gas leakage. The weight of equipment required to control this evaporation rate appears to be prohibitive. Liquid hydrogen, also, is not safe to handle.

Two practical methods of keeping a balloon at nominally constant altitude have been devised, both using the liquid ballast dropping technique. (Solid ballast, such as sand, does not flow well and is liable to absorb moisture which will freeze at the temperatures experienced at high altitudes. Although a few preliminary flights were made with desiccated sand, a highly refined water-free kerosene-type petroleum product,compass fluid,was found to be more satisfactory).

In the simpler control system, ballast is dropped at a pre-determined rate, aimed to slightly exceed the loss of lift of the balloon due to leakage and diffusion. If this method is successfully used, the balloon stays full because the remaining gas in the balloon has less load to support; therefore,