Flight 74: Released from Alamogordo, New Mexico, 1040 MST, July 19, 1948 Not recovered
This was a test of a single 7-foot balloon made of .001" polyethylene, carrying a 4-kilogram payload. One part of the load was the first model of an automatic ballast siphon used to detect and telemeter the amount of ballast being discharged through an automatic ballast valve.
The balloon flew at 7000 feet MSL across a heated desert area and into a mountain pass whose elevation was about 6000 feet MSL. During the first two hours its behavior was reported by radio, and the accompanying timeheight curve (Figure 28) shows how the ballast valve operated successfully
Figure 28
to sustain the balloon. During this turbulent flight about 200 grams of ballast were expended per hour, but the pronounced orographic and convective currents probably necessitated more control than would be required in a more stable atmosphere.
The very useful information about ballast flow was reported clearly, and the principle of the auto-siphon was used repeatedly on later flights. Small variations are seen in the pressure at which the ballast flow began. Since the balloon was floating below the base of clouds, this represents the changes of activation pressure which resulted from changes of superheat of the air entrapped in the aneroid.