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All the upper stages of Juno II, including the gold cone, had been gyrostabilized by spinning at 400 r.p.m. This rapid motion would have kept the moonspotter from operating, so an ingenious system was devised to slow the spin. Two wires about 5 ft. long were wrapped around the base of the cone. On their ends were small (.2 oz.) weights, called "yo-yos'' by their designers. A timer was set to let the wires unwind about ten hours after launch. The yo-yos would swing outward, and the energy needed to make them swing in large circles would be taken from the spin of the cone, making it slow down to about 51 r.p.m.
The overall purpose of this intricate and spider-light gadgetry was to try out a way to trigger cameras and other viewing equipment on the more ambitious space probes of the future. But the moon's image did not grow big and near enough to work the trigger.
Two Geiger counters worked well, should enable scientists to chart more exactly the dangerous Van Allen Radiation Belt that surrounds the earth (TIME, Dec. 8). The core is believed to be about 5,000 miles up. The Explorer satellites have charted its lower levels. The instruments of the Air Force's Pioneer I, the only other object to climb to the belt's upper reaches, did not start working until they reached an altitude where the Van Allen radiation is fading out. If Pioneer III finds the core and ceiling of the radiation belt, its faltering pass at the moon will be rated a scientific triumph.