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Both discoveries come at a critical time. NASA has been planning to launch in 1977 two unmanned spacecraft that would reach the vicinity of Jupiter by 1979 and use Jovian gravity to boost themselves past Saturn in 1981. During these missions, the robots could make close-up studies of the moons, particularly Titan (because of their trajectory, they would pass within 100 miles of Saturn's giant satellite). But now these missions seem threatened. Cutbacks in NASA's budget have resulted in the cancellation of two planned high-energy astronomical observatories, as well as development work on a nuclear rocket-propulsion system. Many scientists fear that the next victims of the economy drive will be the combined Jupiter-Saturn probes. That will be particularly disappointing. After the late 1970s, it will be another 20 years before the planets again come close enough to each other for such a trip.