VOYAGER 2 has bid Neptune goodbye and taken up its new assignment to sample the outer solar system. Magellan - the Venus radar mapping probe launched in May - is well on its way to meet the Evening Star. Now space scientists are eager to launch the Galileo Jupiter mission as this year's third major planetary science event. It will also be the second launch (after Magellan) of six missions that the National Aeronautics and Space Administration (NASA) expects will put the United States solidly back in solar system exploration.
Galileo could be on its way early next week. NASA postponed the launch - originally set for this afternoon - to check out a possibly faulty control system in one of the shuttle Atlantis's three main engines.
In addition, an attempt by three public-interest groups to obtain a court order to block the launch was denied Tuesday evening. They had argued that NASA underestimates the risk of accidental release of the radioactive plutonium that fuels Galileo's two electric power packs. US District Judge Oliver Gasch in Washington ruled that ``it is not the function of this court to decide whether the government's decision to go forward with the Galileo mission is a good one.'' NASA, he said, has enough information ``to ... make a reasoned decision.''
Galileo is the most sophisticated planetary spacecraft NASA has yet flown. It has a battery of instruments that represent more than a decade of design advances since the Voyager equipment was built. It will use these to survey Jupiter and its four large inner moons during at least 10 passes among those satellites. It also carries a probe to sample Jupiter's atmosphere. On the way to meet Jupiter in December 1995, it may have an opportunity to study an asteroid at close range.
If fully successful, this will be one of the most scientifically rewarding planet surveys yet made. The two Pioneer and Voyager craft that have scanned Jupiter got only fleeting glimpses; Galileo should compile a detailed Jovian atlas.
Yet this ambitious mission is only part of a larger exploration. In August, Magellan will reach Venus. In 1992, NASA plans to launch the Mars Observer craft to make a global study of that world. NASA also plans to launch Ulysses that year in a joint mission with the European Space Agency. Ulysses will move high over the unexplored north and south polar regions of the sun.
These are missions delayed since the early 1980s. NASA also has new solar system business in two projects requested to start in fiscal 1990.
One mission, called CRAF for Comet Rendezvous and Asteroid Flyby, is to launch in 1995. It will inspect an asteroid and join Comet Kopff in the year 2000 to accompany the comet as it comes toward the sun.
Space scientists hope to monitor Kopff's evolution as it nears the sun and grows its tail, as well as to sample its surface with a penetrating probe.
The other mission, called Cassini, is to make a detailed survey of the Saturnian system, especially probing the giant moon Titan.
Cassini will leave Earth in April 1996 and reach Saturn in 2002 - more than two decades after the voyagers. It will survey that planetary system for four years. On the way, it too should pass by the asteroid Maja in March 1997.
If and when all these now authorized missions are completed, they will represent a detailed second-generation exploration of the solar system from Venus out to Saturn and also around the sun.
This is the ``big picture'' of which Galileo is but one important part.