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

FIG. 2. Automatic ballast valve.

a diaphragm-operated needle valve which jettisons liquid ballast whenever the balloon is below the altitude at which the control is actuated. This is shown in fig. 2. The ballast reservoir (fig. 3), in general, can hold 15 kilograms of the liquid ballast—usually compass fluid, a highly refined kerosene-type petroleum product. When the atmospheric pressure outside the diaphragm is 5 millibars above the internal pressure, 160 grams of ballast per minute flow under a one-foot head. When the automatic ballast valve is wide open, which is after 6.5 millibars increase over the internal pressure, 300 grams per minute flow. These values may be compared with a diffusion loss of lift of the order of magnitude of 10 grams per hour from the thicker 15-ft balloon described below. Quite positive altitude control can be obtained.

Efforts are made to cause the static rate of leakage, i.e., the leakage which proceeds when the automatic ballast valve is closed, to exceed slightly the rate of loss of lift due to the diffusion of the lifting gas from the balloon. To facilitate setting the fixed leak, a manually operated ballast valve, consisting of a leak adjustable by means of a fine needle valve, is added to the ballast-release assembly.4

C. Minimum pressure switch. Obviously, the automatic ballast valve must not be in operation while the balloon is rising, as this would be a waste of ballast. Therefore the automatically operated needle valve is closed until the balloon reaches altitude. This is accomplished by having the loaded diaphragm of the altitude control open to the atmosphere until the balloon descends from a minimum pressure. At this time, an electrical contact is made and a squib $ ^{5} $ cuts a

restraining cord and allows a needle valve to seal off the diaphragm from any further access to the air (fig. 2). The capsule then contains a volume of air which has been trapped at the existing pressure and temperature, at the time of operation of the sealing switch. Thereafter the aneroid will withdraw the ballast-control needle valve when the ambient pressure increases to the point where the entrapped air is compressed below this volume.

Fig. 4 shows the minimum pressure switch which makes the electrical contact at the time of seal-off. It consists of a trapped volume of air that is allowed to escape through a mercury pool as long as the outside pressure is decreasing. As soon as the exterior pressure increases once more, however, mercury is drawn into the tube, making the seal-off contact between two electrodes.

## 4. Height determination

Up to the present time, the standard radiosonde has been used in order to determine the altitude at which the balloon is flying. This permits a regular radiosonde ascent to be obtained during the period that the balloon is rising. Thereafter, as the balloon remains at approximately the same altitude, it becomes somewhat difficult to identify the radiosonde contact, but utilizing both the temperature and pressure indication, this is possible. A special radiosonde modulator of the Olland type has been designed (fig. 5). The pressure

FIG. 3. Ballast-release assembly.