NASA's Deep Impact spacecraft lifted off yesterday from Cape Canaveral, Fla., on the first stage of a six-month journey to intercept the comet Tempel 1.

When the craft reaches Tempel 1 near the orbit of Mars, it will fire a probe into the comet, digging out a crater perhaps deep enough to hold a 14-story building.

Space scientists hope to discover what comets are made of and whether they are as hard as asteroids or as soft and mushy as gypsum. Scientists also hope to uncover secrets of the early solar system by analyzing the ice and dust ejected when the bathtub-sized probe collides with the speeding comet.

"One of the scary things is that we won't actually know the shape and what it looks like until after we do the encounter," Jay Melosh, a planetary geologist at the University of Arizona, told The Associated Press.

The Deep Impact spacecraft was launched atop a Delta II rocket at 1:47 p.m. EST. Reports from the spacecraft showed it had deployed its solar panels, oriented itself in space and was functioning normally.

Plans call for the probe to collide with the comet just short of Mars' orbit on July 4 after a journey of 268 million miles. If the $328 million mission succeeds, the resulting collision between the probe and comet will cause the comet to flare brightly enough that amateur astronomers should be able to see the celestial fireworks display with small telescopes.

Tempel 1, discovered in 1867 by astronomer Ernst Tempel, is about 9 miles long and about a third as wide. Its 5-1/2-year orbit carries it between Mars and Jupiter.

Comets are largely made up of ice, gas and dust, but much is still unknown. Some scientists think they could be a loose accumulation of space flotsam so fragile that the probe could fly right through it.

More likely, the probe will be obliterated. It carries a camera that will continue taking pictures right up to the point of the crash. The mother craft will stand off about 300 miles, taking pictures and measuring the ejected material with a spectrometer.

Scientists said that even if a portion of the comet breaks off, the collision is so far away that it will pose no hazard to Earth.