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

from the desert set in, the balloon maintained an altitude of 9200 $ \pm 1 5 0 $ ft.

An explanation as to why the ballast release functioned at 9000 ft, although it was set to operate at 12,000 ft, is plain from the following data. The air in the diaphragm was sealed off on the dawn ascent at 12,000 ft, where the pressure was 657 mb and the temperature 9C. However, by the time the balloon passed through this level during the slow descent, the instrument temperature was 19C. This means that the pressure of the air trapped inside the diaphragm was higher than it was at time of seal-off.

For the ballast valve to function, the balloon had to descend to a pressure which would be greater by about 3 mb than the pressure of the trapped air at its now higher temperature. Of course, there was little ventilation past the instrument, and therefore the instrument temperature was about 25C above the ambient temperature after the sun had risen.

The automatic ballast valve operates when the volume inside the sealed diaphragm becomes slightly less than the volume at seal-off. Denoting the altitude at which it can operate by the subscript h, the pressure divided by the temperature at this altitude will equal the pressure at the seal-off altitude divided by the trapped-air temperature at the time of seal-off; in this case

$$
p _ {s} = 6 5 7 \mathrm {m b}
$$

$$
T _ {s} = 9 \mathrm {C} = 2 8 2 \mathrm {A}
$$

$$
T _ {h} = 3 9 \mathrm {C} = 3 1 2 \mathrm {A},
$$

where the subscript s refers to seal-off. Thus the pressure at altitude h is given by

$$
p _ {h} = p _ {s} T _ {h} / T _ {s} = 7 2 7 \mathrm {m b}.
$$

This pressure, at which ballast release will begin, corresponds to an altitude of 9000 ft, which is the observed altitude maintained by the balloon for nearly $ 4\frac{1}{2} $ hours, until the radiosonde tracking signal was lost.

The theodolite lost the balloon in clouds earlier and the airplane observer never succeeded in seeing it, so the balloon may have remained for a considerably longer period at this altitude. Eleven hours after beginning the ascent, the balloon was reported to have been seen over Albuquerque, New Mexico, and about 26 hours later a report was made from Pueblo, Colorado, which seemed to indicate that the balloon was still in the air at that time. The meteorological situation and wind data for that area at the time of flight support the contention that the latter observations were of the same balloon.

The next flight consisted of an assembly of various balloons, as follows:

One 15-ft diameter 0.008-inch polyethylene balloon, Six 7-ft diameter General Mills 0.001-inch polythene balloons,

Two 350-gm meteorological balloons for stadia measurements.

The single balloon had a measured diffusion loss of lift of 4 grams per hour. The General Mills balloons were observed to lose lift at the rate of about 100 grams per hour per balloon.

Three of the 7-ft balloons were inverted and deflated shortly after launching, due to differences in the rates of rise of the various balloons in the cluster. Therefore, the altitude reached was not high enough to effect seal-off. (It is for this reason that the minimum pressure switch was developed for use in later flights.)

Fig. 9 shows the elevation and plan views of the track of this flight. The train leveled off at 16,500 ft. The diffusion loss of lift of the remaining balloons was approximately 300 grams per hour. The ballast valve used had an unusually high rate of static leakage which had been measured before release and found to be 310 grams per hour. Thus fortuitously, the loss of lift was compensated by ballast leakage. This nearly

ALTITUDE (Thousands of Feet)

FIG. 6. Idealized time-altitude curves for various balloon-control systems.