CAPE CANAVERAL, Fla. - Shuttle Atlantis crept up onto its beachside launch pad here at Kennedy Space Center Wednesday, but NASA officials say the agency will be hard pressed to meet a target launch date later this month.

Atlantis and a crew of five astronauts are tentatively scheduled to blast off Jan. 19 on a mission to deliver a U.S. science laboratory to the International Space Station. But a heavy load of work and a tight schedule could ultimately force NASA to push the flight back a day or so.

Shuttle Atlantis is rolled out to the launch pad in this SPACE.com image by Todd Halvorson.

"We're still working toward a launch date of no earlier than Jan. 19," said KSC spokesman Joel Wells. "But we have a very compressed schedule."

Perched atop a giant tracked transporter, the 4.5-million-pound (2-million-kilogram) shuttle inched its way out of the KSC Vehicle Assembly Building early Wednesday. Ambling along at a top speed of just over one mph (1.6 kilometers per hour), the shuttle made the 3.5-mile (5.6-kilometer) trip in about six hours.

The move had been scheduled for Tuesday but was cancelled after a shuttle transporter computer controller crashed about an hour after Atlantis exited the 52-story KSC assembly building. Atlantis then was hauled back into the building and outfitted with another transporter.

The rollout originally had been scheduled for mid-December but was delayed until after the Christmas and New Year's holidays so technicians could repair damaged cables on the shuttle's twin solid rocket boosters.

Technicians will spend the next few days hooking Atlantis up to the launch tower at pad 39A, one of two identical shuttle launch facilities here at KSC.

The 32,000-pound (14,515-kilogram) U.S. Destiny lab - which will be the scientific heart of the station - will be loaded into the shuttle's expansive cargo bay Saturday. Stretching some 28 feet (8.5 meters) in length, the cylindrical module will be the first of six labs that will enable rotating station crews to carry out experiments in a wide variety of scientific disciplines.

The Atlantis crew, meanwhile, will take part this week in a two-day dress rehearsal for launch.

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Led by veteran astronaut Ken Cockrell, the crew will go through emergency training at the launch pad Friday. A day later, the astronauts will board Atlantis for the last few hours of a launch countdown.

The crew also includes rookie pilot Mark Polansky and three mission specialists: Marsha Ivins, Tom Jones and Robert Curbeam.

Expedition One

Look here for the latest news about the first crew to live and work aboard the International Space Station.

Ivins will use the shuttle's 50-foot (15-meter) robot arm to attach the hulking lab to the station; Jones and Curbeam will perform three spacewalks to help install the lab and wire it up to the rest of the 97-ton (88-metric-ton) outpost.

Jones and Curbeam also plan to relocate communications antenna equipment and carry out an emergency drill aimed at determining whether a spacewalking construction worker could haul an incapacitated partner back into the shuttle for medical attention.

A Jan. 19 launch would lead to a Jan. 29 landing here at KSC's shuttle runway.

A firm launch date, however, won't be set until senior program managers meet next Wednesday in a traditional flight readiness review here at KSC.

As it stands, the Air Force's Eastern Range - which is a widespread network of ground tracking stations that supports all Florida space launches - will be available for a shuttle launch on either Jan. 19 and Jan. 20.

Previously scheduled Air Force Titan 4 rocket tests, however, would block any shuttle launch attempt between Jan. 21 and Jan. 23. Consequently, a shuttle delay beyond Jan. 20 would push the Atlantis flight back to Jan. 24 at the earliest.