this switch a circuit is closed when the rate of descent exceeds 1/5 mb/minute, allowing ballast to flow. The record of Flight 97 indicates that good control was obtained for a four hour period using this switch. However, the instrument is so delicate and susceptible to temperature effects that its use is not advised.
E. Flight Simulation
To make laboratory tests on the control equipment just described, a flight-simulation chamber has been built combining a bell jar and a temperature chamber. A drawing of the temperature chamber designed and built at New York University is shown in Figure 17. (Investigation of commercially sold chambers showed that the cost of purchasing a temperature chamber of the size desired would be prohibitive.) First designs called for the use of a freon refrigerating system; however, use of dry ice as a coolant proved to be more advantageous. This chamber, with its automatic control, can hold temperatures as high as $ + 1 0 0^{\circ} \mathrm{F} $ and as low as $ - 9 0^{\circ} \mathrm{F} $ within 50 for a period of several hours. Dry ice consumption at $ - 6 0^{\circ} \mathrm{F} $ is approximately 150 pounds for a 24-hour period.
LOWEST WORKING TEMP. -65° To -70°C ACCURACY OF TEMP CONTROL 0.5°C
Figure 17. Temperature control chamber.
It is possible, using a bell jar for flight-similitude studies, to arrange switches so that the vacuum pump is turned off and on at