Flight 75: Released from Alamogordo, New Mexico, 1010 MST, July 20, 1948 Recovered at Hollister, California
In order to reach higher altitudes than was possible when 20-foot plastic balloons were used, a 70-foot, .001" polyethylene cell was flown on Flight 75. To determine the duration of buoyancy of this type of balloon no controls were used. Despite this, the balloon remained aloft for more than 60 hours and successfully withstood the loss of superheat occasioned by at least two sunsets. From the height-time curve of this flight (Figure 29) the very marked effect of superheat is apparent.
TIME-MST
Figure 29
The record of the barograph was not complete since the clock stopped each night (clearly recording the lowest elevation reached, however) and ran down completely after 56 hours.
Since the small external appendix with cardboard stiffeners was not suitable for the large balloon, a new design with aluminum formed stiffeners (Figure 30) was used. This type of appendix closer worked well on later flights, and it is likely that the long duration of this flight may be attributed in part to satisfactory closing off of the aperture. In addition to