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

FIG. 7. Height-time curve of balloon Flight 17. Released at Alamogordo, New Mexico, on 9 September 1947 at 1647 MST (105th meridian). Recovered near Pratt, Kansas, 530 miles distant.

constant leakage held the balloon at $ 1 6, 8 0 0 \pm 7 0 0 $ ft for 7 hours. The duration of the flight was $ 9\frac{1}{4} $ hours. When the original 2700-gram ballast was expended, the balloon descended rapidly. Even had the automatic ballast valve been functioning, the constancy of altitude would have been the same. This seems to indicate that only a minimum of automatic control is needed, provided that diffusion losses are slightly overcompensated by a constant ballast leak.

Other flights also indicate the importance of a check valve in the balloon appendix to prevent dilution of the lifting gas with air. If this is not done, the altitude reached is far under the theoretical altitude determined by the displacement and gross load.

## 7. Control systems

Two systems of control are possible with the equipment as described. The balloon is controlled between an upper level (ceiling), where the full balloon buoyancy just equals the load, and a lower level (floor), below which the automatic ballast valve operates. Schematic curves for these two systems of control are shown in fig. 6.

In the first system of control the rate of static ballast leakage is greater than the diffusion loss of lift, and the balloon will stay at the ceiling. If it is displaced above the ceiling the buoyancy is insufficient to balance the load and it will descend again. Provided the rate of ballast discharge is greater than the rate of lift by loss of gas this ceiling will slowly rise by valving of gas, and as gas is lost by diffusion. The less the amount of gas the lower the pressure (higher ceiling) must be for the gas to fully distend the envelope. Unnecessary

valving is undesirable and may, in part, be minimized by use of a restraining safety valve set in the appendix, which will allow some slight pressure to be carried in the balloon, preventing gas loss at the peaks of minor oscillations but still valving gas before the balloon ruptures due to too great an internal pressure.

In this system of control, the automatic valve is not sealed off until the balloon starts a descent due to cooling or other changes in lift, as when night falls. Upon descent the valve is activated and starts dropping ballast immediately; this continues until the balloon is no longer losing lift at a rate greater than the diffusion losses. The balloon will then rise above its former ceiling to a height determined by the weight of ballast dropped, and remain there as long as there is ballast to compensate for lift losses. Flight 17, reproduced in fig. 7, used a low-leakage balloon and is an actual case of ceiling control. It may be compared with the idealized time-altitude curves in fig. 6.

In the second system of control the static rate of leakage is less than the diffusion loss of lift. In this case the balloon will descend to the floor, where the automatic control operates and the balloon floats at an equilibrium altitude where the rate of ballast release exactly balances the rate of loss of lift. Floor control conserves ballast, since only that needed for altitude control is released. However, the altitude of the floor varies diurnally as the temperature of the entrapped air in the automatic ballast valve is affected by solar radiation. Two methods are being investigated to circumvent this undesirable feature. One is to

FIG. 8. Wind vectors at 16,000 feet for El Paso (EO), Albuquerque (AB), and Roswell (THJ), at $ 0 3^{\mathrm{h}} $ $ 0 9^{\mathrm{h}} $ and $ 1 5^{\mathrm{h}} $ (MST) on 7 July 1947, in connection with balloon Flight 11, mean motion of which is shown by the balloon vector. Cross-hatched sector contains all wind vectors at these three stations for the three observation hours and for the three levels, 14,000, 16,000, and 18,000 feet.