Launch of NASA's Deep Impact spacecraft that will blast a small projectile into the heart of Comet Tempel 1 has been delayed from December 30 to give engineers more time to complete pre-flight work on mission software, the space agency announced today.

Liftoff is now targeted for no sooner than January 8 at 2:39:50 p.m. EST (1939:50 GMT) from Cape Canaveral Air Force Station's pad 17B.

The mission must launch within a 30-day window that offers the proper trajectory for Deep Impact to reach the comet next July. An 820-pound copper-tipped impactor will be fired from the mothership to slam into the comet's nucleus, excavating a stadium-sized crater that should expose pristine material buried in Tempel 1 since the solar system formed more than four billion years ago.

"While there are no significant problems associated with the spacecraft hardware, additional time is necessary to be ready for launch. Spacecraft functional and mission readiness tests continue," a NASA statement said.

At launch pad 17B, the Boeing Delta 2 rocket to launch Deep Impact is being assembled. The first stage was erected Monday and three solid rocket boosters were attached Tuesday. The remaining six solids will be installed in sets of three next week, followed by hoisting of the second stage atop the vehicle.

The next Delta launch is scheduled for December 10 when the inaugural Delta 4-Heavy flies a demonstration flight for the U.S. Air Force. The giant vehicle will launch from pad 37B at the Cape during a window of 2:31 to 5:27 p.m. EST (1931-2227 GMT).