July 1, 2005

NASA craft ‘healthy and ready’ for comet collision

By Nichola Groom

PASADENA, Calif. (Reuters) - A NASA spacecraft is "healthyand ready" for its July 4 collision with a comet and hasalready provided images critical to understanding the buildingblocks of life on Earth, officials said on Friday.

While still roughly 1.5 million miles from its target, thefast-moving Deep Impact craft is on track for its Saturdayrelease of a coffee-table sized impactor that is expected toblast a stadium-sized crater into comet Tempel 1.

"Both the fly-by and the impactor spacecraft are healthyand ready for encounter operations," Deep Impact's missionmanager, Dave Spencer, told reporters at NASA's Jet PropulsionLaboratory in Pasadena.

At 1:52 a.m. EDT (0552 GMT) on Monday, the 771-pound (350kg) copper-fortified impactor is expected to smash into thecomet at 23,000 mph (37,010 kph), a speed that would make theflight from New York to Los Angeles a mere 6 minutes.

Although all of the spacecraft's systems appear to be inworking order, officials said there were contingency plans inplace if the impactor failed to detach from the ship. Onealternative includes sending both to collide with the comet.

Tempel 1, which JPL scientist Don Yeomans described as "ajet black, pickle-shaped, icy dirt ball the size of WashingtonD.C.," will be about 83 million miles away from Earth at thetime of the crash.

The aim of the mission, the first to come in direct contactwith a comet's nucleus, is to photograph material formedbillions of years ago during the creation of the solar system.

"These materials have not seen the light of day for 4.6billion years," said Jessica Sunshine, a scientist working onthe mission. "That's what we're waiting to see."

Comets are made of gas, dust and ice from the solarsystem's farthest regions. They often show bursts of activity,during which their surfaces crack to create tails of dust.

Deep Impact has already recorded several such outburstsfrom Tempel 1. NASA scientists said the data has shown thatsmall outbursts, which they called "sneezes," are more commonthan they had previously thought.

The biggest "sneeze" witnessed so far doubled the amount ofwater in the comet's coma, or atmosphere, they said. Scientistshave long held the theory that comets first brought water toEarth by crashing into its surface.

The outbursts are not big enough to blow the mission offcourse, according to NASA, though Spencer said the impactor wasin for "a bumpy ride" as it approached the comet. Using itsautomatic pilot, the impactor will have three opportunities toadjust its trajectory in the 2 hours leading up to the impact.

The main spacecraft will be about 310 miles away from thecomet at the time of the crash and will have about 13 minutesafter the blast to capture images and data before it weathers ablizzard of particles thrown out of the comet's nucleus.

There are cameras aboard both the impactor and the maincraft, and the blast will be observed by the Hubble, Spitzerand Chandra space telescopes.