On to Saturn

NASA's manned space program may be suffering from hard times, but the space agency's unmanned exploration of the solar system is continuing to report stunning successes. In the past few years, robot spacecraft have surveyed the planet Mars in exquisite detail, sent back the first closeup pictures of Venus and Mercury, and penetrated the powerful radiation belts surrounding the sun's largest satellite, Jupiter. Now, after sweeping even closer to Jupiter than did its predecessor, Pioneer 10, last December, Pioneer 11 is beginning the long trip to its next target: Saturn.

The arcing, 1.5 bill ion-mile voyage across a large part of the solar system will take five years, but flight planners at NASA'S Ames Research Center have every reason to expect the 570-lb. nuclear-powered robot to survive the trip. If it does, it will send back closeup pictures and other data from the ringed planet. Of four Pioneers that were launched into solar orbit between 1965 and 1968 to monitor interplanetary space, all are still transmitting scientific data--even though they were designed by Pioneer's prime contractor, TRW Inc., to last only six months; only one is experiencing some difficulty with a solar sensor. Signals are also still coming from Pioneer 10, which is now heading out of the solar system. Says Pioneer Project Scientist John H. Wolfe: "We now figure that if they make it for six months, they'll probably last forever."

Kamikaze Mission. Pioneer ll's longevity will be threatened in September 1979, when it swoops between Saturn and the innermost of its three rings on what Wolfe admits could be a "kamikaze mission." The spacecraft could be knocked out of action in a collision with a chunk of the ring's icy debris, some of which may be up to half a mile across. Otherwise, it will pass as close as 1,850 miles from Saturn's cloud tops (compared with 26,725 miles from Jupiter's). It will then be whipped around Saturn by the planet's powerful gravity and sent on a looping path toward Titan, Saturn's biggest moon. Even larger than the earth's moon, Titan may have an atmosphere and harbor some forms of life. To avoid risk of a collision that could contaminate Titan with earthly bugs, Pioneer will come no closer than 12,000 miles. Finally, the spacecraft will head out of the solar system, sending back signals that should continue at least until it reaches the orbit of Uranus (in 1985). After that the signals will be so faint that not even the largest antennas on earth will be able to pick them up.

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