The crew will get the news when they wake up Friday night for their first full day in orbit.

"First thing in the morning, well give you the outcome of their discussion," Canadian astronaut Steve MacLean told the crew from NASAs Mission Control Center in Houston. "And were all hoping that we can rendezvous with the Hubble and fix it."

The potential mission showstopper cropped up just before the shuttles two cargo bay doors swung open about 85 minutes after a sunrise liftoff from Kennedy Space Center.

A warning message seen on computers both onboard Columbia and in Mission Control showed that the flow of coolant within the shuttles portside radiator had dropped to a level that approached safety limits.

The coolant flow returned to normal once the clamshell-like doors opened. But engineers suspect that the problem could crop up again when the doors are closed prior to a return to Earth.

The coolant loops within the two radiators -- which are located on the inner side of each of the doors -- are considered key to cooling sensitive spaceship electronics throughout a flight and during a supersonic dive back through the planets atmosphere.

The flight rule calling for a quick return to Earth aims to guard against the chance that both shuttle radiators might break down during orbital operations.

A similar situation cropped up during Columbias last flight, a July 1999 mission to deploy NASAs $1.5 billion Chandra Observatory, a Hubble-class x-ray telescope.

In that case, restricted coolant flow was seen in the same port radiator, but the five-day mission went on as planned. Columbias flight is slated to last 11 days.

Another mission-threatening problem also cropped up -- but was overcome -- as the crew moved to open the ships inner airlock hatch, the initial orbital portal for the astronauts who will be servicing Hubble.

Working side by side with crewmate James Newman, Altman tried to turn a hatch handle but simply couldnt get the hatch to unlatch during an initial attempt. But Newman gave it a try and quickly reported success.

"I fixed it," Newman radioed down to Mission Control. "What I did this time is when I went to unlock, I kept the handle hard and flush against the airlock, and the handle is now rotating effortlessly."

"Thats excellent news," MacLean called back.

Columbia suffered a similar problem during a November 1996 mission when astronauts Tom Jones and Tammy Jernigan couldnt get the airlock hatch to open. A spacewalk planned for the flight had to be scrapped as a result.

A stuck airlock hatch, meanwhile, would prevent Columbias telescope repair crew from setting out on any of five planned spacewalks.

The double dose of trouble came on the heels of a virtually flawless dawn launch from NASAs Kennedy Space Center.

Fresh off a $100 million overhaul, the veteran spaceship blasted off at 6:22 a.m. EST (1122 GMT), punching its way through partly cloudy skies as it arced out over the Atlantic Ocean and rocketed into orbit.

The $3 billion Hubble telescope could be seen passing 362 miles (579 kilometers) over the launch site as Columbia climbed toward orbit, the ships twin solid rocket boosters trailing sunlit white contrails as they tumbled toward the ocean.

"It was something that was a sight to behold -- absolutely extraordinary," said new NASA Administrator Sean OKeefe, a former White House budget official who was attending his first shuttle launch.

"We saw them almost all the way to splashdown, which was unprecedented, as far as Im concerned," added NASA shuttle launch director Mike Leinbach. "It was just a beautiful launch."

The launch set the stage for one of the most ambitious shuttle missions in NASA history.

During the planned spacewalks, the astronauts aim to equip Hubble with a fresh set of solar wings, install a new planetary camera, resuscitate a dead science instrument, replace a faulty pointing control device and overhaul the observatorys electrical system.

"Theyve got an important mission ahead of themselves," OKeefe said. "Theyre up there now on their way to five spacewalks in order to service the Hubble telescope, and thatll be a historic event all by itself."

A shortened flight, on such a high-stakes mission, would be historic, too. Only three shuttle flights to date have been cut short by technical problems, two for fuel cell failures and the other when a key guidance control unit broke down in orbit.

As it stands, Columbia and its crew remain scheduled to rendezvous with the 13-ton telescope at 4:14 a.m. EST (9:14 GMT) Sunday. A full mission would lead to a landing here at NASAs coastal Florida spaceport on March 12.