Tense, excited men gazed spaceward from the ships and planes of the South Atlantic task force. Other watchers waited breath-lessly in the control room of the ship Recoverer. Among these was Tom Swift Jr. "How close to earth is our Jupiter probe missile?" Bud Barclay asked Tom excitedly. The lanky blond youth beside him, in T shirt and slacks, shot a glance at the dials of the tracking equipment. "Eight thousand miles from this spot, Bud. It should land here in fifteen minutes!" Tom Jr., his father, Bud, and a host of scientists, Navy officers, and newsmen were crowded aboard a U.S. Navy missile launching ship. "Just think!" Bud exulted. "You'll have data from the planet Jupiter that no one on earth has yet been able to get!" "If we recover the missile safely," Mr. Swift spoke up hopefully. The elder scientist's voice was quiet but taut with the strain of waiting. The two Swifts resembled each other closely - each had deep-set blue eyes and clean-cut features - although Tom was somewhat taller and rangier.