The 3.5-mile (5.6-kilometer) trip had been scheduled for Wednesday but was delayed when the Apollo-era transporter broke down after it began moving out of the assembly building.

Mechanics spent two days repairing the crawler, but the move to the pad then was postponed again because a frontal system is expected to bring rainy weather into the Cape Canaveral area during the weekend.

Columbia remains scheduled to blast off at 6:53 a.m. EST (1153 GMT) Feb. 28, and the shuttle that sets sail that day will be a leaner machine than the orbiter that last flew in July 1999.

A veteran of 26 flights and 224 days in space, Columbia no longer is weighed down by some 600 pounds (270 kilograms) of developmental flight instrumentation and associated wiring that was used to gather systems data during its first four missions.

Thermal blankets also have replaced heat-resistant tiles in some locations on the ship, further reducing the total weight of the vehicle.

An advanced cockpit with 11 full-color, flat-panel displays has been put in place on the shuttle's flight deck, replacing 32 mechanical gauges that were more difficult for mission commanders and pilots to operate.

The new "glass cockpit" is lighter than its predecessor and also uses less electricity.

All in all, some 100 modifications and improvements were made to Columbia during an 18-month overhaul that preceded the shuttle's return to KSC for Hubble flight preparations.

Among others: A series of radiator valves that will enable crews to isolate leaks triggered by debris or micrometeorite hits to the heat-dissipating devices, which are located on the inside of the ship's clamshell-like cargo bay doors.

Columbia's crew cabin floor was beefed up so that it could sustain a 20 g crash load, and the orbiter also was put through the most extensive wiring inspection ever conducted on a shuttle.

The failure of two crucial engine computers on its last flight prompted NASA managers to order up extensive wiring inspections that subsequently grounded the agency's four-orbiter shuttle fleet for five months in late 1999.

Engineers traced the computer failures to an electrical short and later determined that workers inadvertently damaged wiring during routine pre-launch processing.

As a result, more than 190 miles (304 kilometers) of wiring within Columbia -- or 95 percent of the ship's electrical cabling -- was inspected during the shuttle's stay in California.

Roe said the remainder of the wiring is inaccessible -- buried within the shuttle's wings and fuselage -- and not susceptible to damage.

During the inspections, about 1,000 wiring problems were noted and repaired, and technicians installed protective tubing around electrical cables in work areas exposed to "high traffic" during normal launch preparations.

NASA's other three orbiters -- Discovery, Atlantis and Endeavour -- will undergo similar work when they are sidelined for periodic overhauls over the course of the next several years. About 50 percent of the wiring in those ships was checked out during fleet-wide inspections in 1999.

The wiring work on Columbia, meanwhile, included the installation of electrical cabling that will allow NASA to equip the ship with a docking system so that it too can serve as a courier to the International Space Station.

NASA's three other shuttles have flown all U.S. missions to the station to date, primarily because those ships are capable of flying up to the outpost with bus-sized modules and other heavy cargoes.

Columbia, however, now is light enough to be launched to the station on crew rotation missions, and tentative plans are being put in place to do just that.

With sistership Discovery about to undergo a lengthy overhaul, its docking system is to be removed and installed in Columbia when the latter returns from its second 2002 flight -- a research mission now scheduled for launch in late June.

Thus equipped, the shuttle then is to be readied for a late September 2003 mission to ferry the station's eighth full-time crew to the outpost and then return to Earth with its seventh.

Nestled into its cargo bay for that flight: a pressurized Spacehab Inc. cargo module filled with outpost supplies and equipment and a single piece of the station's segmented central truss, which eventually will extend some 356 feet (108 meters) from end to end.

The STS-118 flight currently is scheduled for launch Sept. 25, 2003. Discovery originally was tapped to fly the mission but that ship won't be available because of a later-than-anticipated start on its upcoming overhaul.

Columbia's recent weight reduction program, consequently, is providing NASA with a new option for getting to and from the station when the agency's other orbiters undergo modifications.

"It definitely adds flexibility," said Ed Mango, a NASA launch manager here at KSC.

The extensive wiring work and other improvements, meanwhile, are expected to make Columbia less susceptible to the type of in-flight failures that plagued its last launch, a mission during which the Chandra X-ray observatory was deployed.

"It's returning to space now with more capability, and it's safer than it's ever been," said JSC spokesman James Hartsfield. "And I think that epitomizes the goals of the shuttle program."