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Tony Reichhardt,Washington experimental control that scientists Scientists gearing up for the most gain by creating their own observ- ambitious planetary mission in ing sequences. But, he says, the new history say it will also be the strategy carries some risk.While all most demanding for them. For commands will be checked by JPL the Cassini mission, NASA has before they are sent to Cassini, to shifted much of the hands-on ensure that they do not jeopardize ASA/JPL/SPACE SCIENCE INST. ASA/JPL/SPACE planning from the agency’s own the spacecraft, some observations N centres to the instrument teams could be less efficient than they in the universities. might be,as a dozen different teams The US$3.2-billion US–Euro- are involved in the sequencing. pean spacecraft is set to arrive at Scientists are reluctant to com- Saturn on 1 July to begin a four- plain about funding, however, year, 74-orbit tour of the giant gas with Cassini’s price tag reaching a planet, its rings and its moons. cool $3.2 billion. That includes While a dozen instruments on the $400 million for the launch, $750 main orbiter study the Saturn million paid by European coun- system close up and map its elec- tries, and $720 million to operate tromagnetic field, the attached Cassini and keep the science European-built Huygens probe teams funded until the end of the will drop down in January to the mission in 2008. surface of Titan, the planet’s And Cassini’s investigators are largest moon. Getting closer: Saturn as seen from the Cassini spacecraft last month. looking forward to the richest sci- Similar in design to the Galileo entific bounty of their careers. mission that explored Jupiter and its moons of the work was “thrown over the fence” to Close study of the intricate ring system in the 1990s, Cassini will be “like Galileo on the outside scientists, says Stamatios Krim- should teach researchers about the dynamics steroids”, says Torrence Johnson of the Jet igis of the Johns Hopkins University Applied of similar disks surrounding other stars. Sat- Propulsion Laboratory in Pasadena, Califor- Physics Laboratory in Laurel, Maryland, urn’s moon Enceladus may turn out to be nia,a member of the Cassini imaging team and principal investigator for one of Cassini’s geologically active, with water geysers spout- former Galileo project scientist. Not only will magnetospheric experiments. ing above its icy surface. Titan, with its Cassini cram far more observations into half That allowed JPL to cut its operational constant haze and Earth-like, nitrogen-rich the time, data from the spacecraft will pour in budget for Cassini by some 40% compared atmosphere, is a mystery that planetary much faster than it did from Galileo, which with that of Galileo,according to Mark Dahl, scientists have long wanted to crack. And was hampered by a jammed antenna. NASA’s programme executive for Cassini. because Cassini will return hundreds of Scientists have had far more responsibil- But project scientists complain that they thousands of images of the planet’s swirling ity for the details of the Cassini mission than have had to absorb the extra work without clouds, researchers will be able to create they had with Galileo and with the Voyager adequate funding from NASA. extensive movies of the turbulent atmos- missions that surveyed Jupiter, Saturn and The problem was compounded by another phere — something they were unable to do at the outer planets in the 1970s and 1980s and NASA money-saving decision back in 1992. Jupiter because of Galileo’s antenna problem. are now out in deep space.On those projects, Instead of mounting the cameras on a sepa- Cassini entered Saturn’s sphere of gravita- investigators who had built cameras and rate platform so that they could be directed tional influence in mid-May. The action heats other sensors requested where their instru- independently of other instruments, they up on 11 June, when the inbound spacecraft ments should be pointed and when, and were fixed to the spacecraft body, making all makes its first close pass of a moon, tiny technicians at JPL worked out the complex Cassini’s sensors interdependent. This makes Phoebe. Then on 1 July, Cassini’s main rocket sequences of spacecraft manoeuvres needed it far more difficult to plan the observation engine will fire for 94 minutes to brake the to carry out the observations. manoeuvres. “The complexity of the job was spacecraft into orbit around Saturn and begin But when Cassini was being planned in underestimated,” says Krimigis, a sentiment four years of intensive exploration. Compar- the early 1990s, NASA decided that instru- echoed by other Cassini investigators. ing the pace of those observations to the ment teams would work the manoeuvres out Larry Esposito of the University of Col- United States’ best-known car race, Dahl says: for themselves — partly to give the scientists orado in Boulder,who built Cassini’s ultravio- “Scientists are looking forward to the start of more control and partly to save money.A lot let-imaging spectrograph, likes the additional the Indianapolis 500.” ■

NATURE | VOL 429 | 3 JUNE 2004 | www.nature.com/nature 489 © 2004 Nature Publishing Group