Secrets Of The Rings

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COME HITHER: Cassini snapped this picture when it was 17.6 million miles from Saturn; each pixel in the image covers 105 miles

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Cassini's best shot at the moon will come on Christmas Eve, when the Huygens probe is fired toward Titan, heading for a Jan. 14 rendezvous. On arrival, it will make a 2 1/2-hr. descent through the atmosphere by parachute. If it isn't destroyed by the landing, the probe could survive on the surface for an extra 30 minutes or so.

The brief three hours that Huygens lasts will be busy. The probe carries six instruments, including radar, an aerosol collector, a camera and wind instruments. The hardware will switch on by an altitude of 93 miles and will record data all the way down. When Huygens lands, sensors will continue to take readings — assuming it doesn't smack against a mountain or capsize in a methane lake. Even if it does, the landing — NASA's first splashdown since the return of the last Apollo spacecraft in 1975--would make space history.

Barring breakdowns or accidents, Cassini should send back data at least until 2008. If it exceeds its nominal life span it could survive for nearly a decade. When it finally does wink out, it could mark an end in more ways than one.

Cassini-Huygens is widely thought to be the last of NASA's great Cadillac probes — multibillion-dollar ships stuffed with instruments and complex backup systems. In the planning stage for 19 years, the craft cost $1.4 billion to design and build and nearly $2 billion to fly. When NASA adopted its "faster, better, cheaper" philosophy in the 1990s, it drove the cost of its unmanned ships down to the range of a couple of hundred million dollars — mostly by relying on off-the-shelf parts and eliminating redundant systems.

But the frugality came at a price. Cheap ships can't carry as many instruments as luxury models, so it may take more than one mission to bring back the same science. What's more, the lower price means more frequent breakdowns, as the string of bad luck NASA had with its Mars probes in the 1990s painfully demonstrated. The upside of flying economy is that if one spacecraft is lost, it's a relatively small matter to cobble together another. That thrift-shop technology has succeeded in getting three rovers onto the surface of Mars and will be at work again this summer when NASA launches the MESSENGER probe for a 2008 rendezvous with Mercury, and in 2006 when the New Horizons spacecraft takes off for Pluto.

Not all NASA scientists are impressed by these plans. Many believe there would be plenty of money to fly top-shelf ships if the space agency would drop its preoccupation with manned space travel. The International Space Station has been a scientific black hole, swallowing nearly $100 billion and delivering little of real value. President Bush's manned moon-Mars initiative will cost at least $170 billion — and that's from an agency that has never met a cost estimate it couldn't overrun. Forget the fixation with getting bodies in orbit or boots in the soil, critics say, and you could fairly blanket other planets with Cassini-quality landers and orbiters and still have billions left over. NASA administrator Sean O'Keefe, not surprisingly, disagrees: "Robotic missions are precursor missions." The most thorough exploration, he says, "requires the unique cognitive skills that only human beings can bring to the equation."

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