To The Galileo Mission Contents PageA major milestone was reached on July 17, 1982 with the successful balloon drop of a test model of the Galileo Probe. The following is condensed from an article by Don Kindt, Galileo's Probe Spacecraft System Integration Manager at JPL.
The Galileo Probe is designed to be carried to Jupiter by the Galileo Orbiter and then released to enter the Jovian atmosphere on its own. After a fiery red-hot entry, the Probe will shed its protective heatshield and descend by parachute through the atmosphere of Jupiter, sending data back to the Orbiter until the heat and pressure of the Jovian atmosphere destroy the descent module.
How can the Probe be tested here at Earth to make sure that it will work at Jupiter? The only practical way is to lift a test Probe high above the Earth by balloon and drop it. So, on July 17, a test model of the Galileo Probe was dropped at White Sands Missile Range, New Mexico, to test the Probe's separation mechanisms and parachutes.
Months of preparation were required to bring together all the test equipment. The test Probe was built by General Electric Co., subcontractor to Hughes Aircraft Co., the prime contractor to the Probe developer, NASA's Ames Research Center. The balloon was provided by the Air Force Geophysical Laboratory, and final tracking and recovery was coordinated at Holloman Air Force Base.
Wind conditions were monitored carefully until the right conditions existed for the test. Not only did the winds have to blow from east to west at these altitudes, but they had to blow fast enough to carry the balloon over White Sands before the batteries ran out onboard the Probe and the supporting Air Force gondola. The drop also had to occur in daylight so the events could be recorded on film. (Ed. note: Photographs were not available at press time.)
The Probe was held in the Air Force gondola, which is like an upside-down basket. The gondola provided predrop power, heating, movie cameras, and other balloon-related equipment. The gondola (with its Probe cargo) was rolled out of the hangar, hoisted on a portable test crane for weighing, and then transferred to the huge portable launch crane to hang suspended above the ground until the moment of launch.
Meanwhile, the 122-meter-long (400-foot) polyethylene balloon was carefully unpacked from its 1.8-meter-square (6-foot) container and stretched out along the deserted runway at Roswell, N.M. Inflation with helium began about one hour before launch, until the 14,546-cubic meter (5.14 million cubic foot) balloon expanded, rose, and tugged at its tether. [After launch, at 30-kilometers (18 miles) altitude, its diameter expanded to about 71 meters (233 feet).]
As the launch command was given shortly after dawn, a minor hitch in the release mechanism required a sledge hammer. The problem solved, the payload crane truck (with its dangling payload) was driven in the direction of the wind until the truck was directly under the rising balloon and the payload was towed skyward by the rapidly ascending balloon.
Five hours after launch, having been carried about 193 kilometers (116 miles) west by winds up to 66 km/h (40 mph), the Probe was released. It freefell to an altitude of 17.46 kilometers (11 miles), where the pilot chute deployed (its speed was Mach 0.998 ). At 16.94 kilometers (10.5 miles), the main chute deployed and the aft cover released, and at 16.42 kilometers (9.9 miles), the heat shield separated from the descent module. Moments apart, the pilot chute and after cover smashed to the ground at 68 km/h (41 mph), and the main chute and Probe descent module at 61 km/h (37 mph).
The balloon was destroyed by command several minutes after Probe release, and the gondola drifted to the desert floor on its recovery parachute. A crew was sent to pick up the parts of the Probe and to recover the gondola for future use on other Air Force jobs.
All data and pictures will be analyzed to confirm that everything worked according to design. If so, the next stop is Jupiter!
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