As the balloon system approached the ceiling altitude, the excess lift (referred to as "free lift") that drove the system upward on launching filled out a duct system of the lifting balloon, and helium was automatically vented from the lifting balloon and slowed the ascent. As this process continued, the balloon system slowly ascended to the ceiling altitude and was in equilibrium, the lift of the helium balloon just balancing the total weight of the system. If this process took place as designed, about thirty minutes were needed to assure that the system was stable at the ceiling altitude of . If the system instruments indicated that the altitude was not changing, the blower attached to the sample envelope balloon at the base of the system was initiated by the controller. The effect of turning on the blower was almost immediately evident in the appearance of the sample balloon. Viewing the system through a tracking telescope clearly showed the sample envelope beginning to fill out. The sample gathering process typically required of the order of an hour or so to be completed, the appearance of the system then being of two balloons, one immediately on top of the other. The blower was then turned off by the controller and a valve closed that sealed the sample envelope from the outside. The autopilot was then activated by the controller, releasing helium from the lifting balloon (#116) and initiating a descent of the entire system. In practice, the descent of the system did not become apparent for of the order of an hour after the autopilot was activated. This was because the sample balloon, now containing a large volume of air, would generate lift with any descent due to adiabatic heating of the sample air in the isothermal stratosphere. It could require an hour or two to establish a nominal descent rate of the system. The descent to altitudes of the order of could take of the order of two to three hours. At this point the axial fan (#29) was automatically initiated to transfer air in the sample balloon into the armored vessel. This transfer was usually completed before the system reached an altitude of 4 or 5 thousand feet and a valve in the armored vessel valve just above the axial fan (#25) was sealed by the controller. As the system continued to descend and touched down, explosive cutters fired