The analysis isn't over yet, but shuttle program manager Ron Dittemore says he is optimistic Columbia is in a good configuration and can safely continue its ambitious mission to service the Hubble Space Telescope for at least another 24 hours despite a problem detected today with a key cooling system.

Mission managers will meet again on Saturday to discuss the matter but for now the shuttle will be allowed to remain in space and continue its chase of Hubble with plans to grapple the great observatory early Sunday morning.

Dittemore did not shed a lot of additional light on the problem that was seen about 90 minutes after launch, just before Columbia's payload bay doors were opened. That's when flight controllers saw a decreased rate of flow in a Freon-21 coolant line. The flow rate diminished to a point near a redline that would have forced officials to order Columbia home at the earliest opportunity.

Understanding the shuttle's cooling system is a challenge as there are several interconnected sets of plumbing that are used to move heat away from the shuttle's electronics and then several different methods for taking that heat and getting rid of it depending on where in the mission you are.

For those who want to take a crack at it, here's a helpful page from NASA's space shuttle reference manual that sort of summarizes how the cooling system works.

The astronauts are asleep at this hour. They will be awakened with the relatively positive news at 9:22 p.m. EST.

We will be posting a new story shortly and then our next update in this space will come tomorrow morning.

Cautious optimism continues in space and on the ground, but the fat lady hasn't sung yet on the decision over whether Columbia and its suspect cooling system will remain in space for its full mission.

NASA's Mission Management Team will meet at 1 p.m. EST today to decide if the cooling system is stable enough to remain in space and will work well enough to get the crew safely home at the conclusion of this scheduled 11-day voyage to service the Hubble Space Telescope.

So far the numbers appear to be good. Coolant loop 1 is operating in a slightly degraded condition, but is still well within acceptable limits. Coolant loop 2 is working normally. The attention now is on coolant loop 2 as managers want to be sure it will not begin acting up.

Flight controllers briefed the crew on the latest thinking before three of the astronauts were interviewed by news media, informing them that things were looking better for a full mission, but, again, a final decision would not be reached until later today.

For those who want to take a crack at it, here's a helpful page from NASA's space shuttle reference manual that sort of summarizes how the cooling system works.

We will update this space again following the conclusion of the 1 p.m. EST briefing today.

Mission managers have approved the continuation of Columbia's flight to service the Hubble Space Telescope.

The decision means that officials have confidence that the shuttle's suspect cooling system will work fine, not only for the rest of the mission in space but also during the return to Earth scheduled for March 12.

That also means that when the crew is awakened for the second full day in space a little later this evening, they will press on with plans to rendezvous with Hubble and use Columbia's robot arm to grapple the observatory at 4:14 a.m. EST Sunday.

Shuttle program manager Ron Dittemore cautioned that engineers will continue to monitor Columbia's systems very carefully and if things should become worse they may still have to make changes to the flight plan. But for now they are confident that some kind of foreign debris is blocking the flow and that the debris is being held in check by a filter.

The crew, who are asleep now, spent their first full day in space preparing for the events ahead by testing the Canadian-built robot arm and checking out the spacesuits that will be used during the planned five back-to-back spacewalks needed to accomplish all the work on Hubble.

We will post a story with the details of this decision in a just a little bit, and then our next update in this space will come early Sunday morning as Columbia approaches the great observatory.

Columbia's orbital maneuvering engines have been fired in what is officially the final rendezvous maneuver that puts the shuttle on an intercept course with the Hubble Space Telescope.

Small course-correction burns are planned before commander Scott Altman manually flies Columbia close enough to Hubble so flight engineer Nancy Currie can grab the telescope using the shuttle's 50-foot-long robot arm.

The grapple is scheduled for about 4:13 a.m. EST.

Once Hubble is on the end of the arm, Currie will slowly move the observatory to a table at the back of the cargo bay and lock it in place. Hubble will be twisted and tilted atop the table so that the crew can watch as ground controllers command the telescope to roll up its electricity-generating solar array blankets.

NASA TV is available by clicking on the link above. Live views of Hubble are expected as Columbia closes in.

And stay tuned to this page for updates during the next few hours as the telescope is grappled, placed in the cargo bay and its solar arrays are retracted.

Once again the Hubble Space Telescope, an astronomical treasure for more than 10 years, is firmly attached to the end of a space shuttle robot arm, the first step in a week-long effort that will outfit the observatory with new and refurbished instruments and control systems.

After mission commander Scott Altman pulled Columbia to within a robot arm's distance of the telescope, flight engineer Nancy Currie piloted the shuttle's Canadian-built robot arm to reach out and take hold of Hubble, which was designed and built from the start to accommodate this very maneuver.

The final portion of the rendezvous was carried out in appropriately slow and measured steps, the official grapple time coming at 4:31 a.m. EST, some 18 minutes later than called for in the flight plan.

Within the next hour or so, Currie is to slowly move the telescope onto a Lazy Susan-like work table that is in the rear of the cargo bay and lock Hubble in place. Then an electrical plug is to be extended from the cargo bay and inserted into Hubble to provide it with power.

Later this morning, beginning about 8:27 a.m. EST, the observatory's two solar array blankets will be ordered to roll up in preparation for their replacement during the first two spacewalks planned for early Monday and early Tuesday. If the arrays jam or fail to roll up for any reason, spacewalkers will have to remove them and literally throw them away.

Stay tuned to this page for another update in about two hours.

The Hubble Space Telescope sits firmly locked in place atop a work table in Columbia's cargo bay.

Much like a Lazy Susan, the work bench is capable of spinning Hubble around so that its different sides can be presented toward the nose of the shuttle, allowing spacewalking astronauts to access all of Hubble's compartments with ease.

After grabbing Hubble with the shuttle's robot arm at 4:31 a.m. EST, flight engineer Nancy Currie moved the observatory toward the rear of Columbia's bay and placed it on the specially-made platform at 5:26 a.m. EST, where it was latched down seven minutes later.

At 5:49 a.m. EST an electrical umbilical was remotely plugged into Hubble to provide power to the observatory while its solar arrays are replaced this week.

Later this morning, beginning about 8:27 a.m. EST, the observatory's two solar array blankets will be ordered to roll up in preparation for their replacement during the first two spacewalks planned for early Monday and early Tuesday. If the arrays jam or fail to roll up for any reason, spacewalkers will have to remove them and literally throw them away.

Stay tuned to this page for another update once the solar arrays are folded up later this morning, about 10 a.m. EST.

Take a look at the latest story posted above right for a wrap up of the overnight activities and a preview of what's in store tonight.

For now the crew have about two hours left in their work day and most of that will be spent on personal and daily housekeeping chores. Officially they are to go to bed at 12:52 p.m. EST and then be awakened at 8:52 p.m. EST tonight.

Once awake tonight the crew will move into their final preparations to support the first of five planned spacewalks to service the Hubble Space Telescope, which now sits securely in Columbia's cargo bay with its solar array blankets all rolled up to be removed.

Unless something unusual happens during the day, our next update to this page will come shortly after midnight just before the spacewalk is about to begin.

Enjoy your Sunday.

Columbia astronauts John Grunsfeld and Rick Linnehan are nearly ready to step outside and begin the first of five planned spacewalks to work on the Hubble Space Telescope.

The first extravehicular activity is expected to begin within the hour. If you're watching on NASA TV -- available from SPACE.com via our link above -- you can tell the two crewmen apart by the fact that Grunsfeld's spacesuit has red stripes on it, while Linnehan's has no markings.

The major task for tonight is to swap out the starboard solar array on the telescope.

We will post updates every couple of hours during the spacewalk, so fire up the coffee machine and enjoy the show. And if you have any questions or would just like to say hi, please feel free to drop me a note.

An ambitious week of excursions into the vacuum of space has kicked off as Columbia astronauts John Grunsfeld and Rick Linnehan have officially begun the first of a record-tying five back-to-back spacewalks scheduled for this STS-109 mission to service the Hubble Space Telescope.

The official start time of 1:37 a.m. EST was marked as the pair of spacewalkers began relying on their suit batteries for power -- essentially the point where they have become two spaceships no longer dependent on the shuttle mothership for life support.

Both spacewalkers are still inside Columbia's airlock but will be departing almost immediately.

Grunsfeld -- whose spacesuit is marked with red stripes -- is a spacewalking veteran who has already spent time working on Hubble during a past servicing mission. Linnehan -- whose suit has no special markings -- is a rookie, so he'll be given a few moments to get his "space legs."

Then the timeline basically calls for some initial set up work involving their tools, installing a post on the Lazy Susan-like table that is holding Hubble to help keep the table more stable, adding a portable foot restraint to the end of Columbia's robot arm and the like.

The major task of the spacewalk will follow, namely the replacement of Hubble's starboard electricity-generating solar array blanket with a new wing that is smaller, heavier and capable of generating more power for the telescope.

You are invited to watch the spacewalk via our feed of NASA TV, available by the link above. We will post updates every couple of hours during the spacewalk, so fire up the coffee machine and enjoy the show. And if you have any questions or would just like to say hi, please feel free to drop me a note.

Two hours into this morning's spacewalk and John Grunsfeld and Rick Linnehan have removed and stowed the old, starboard solar array from the Hubble Space Telescope.

With Grunsfeld wielding an automatic pistol-shaped screwdriver, and Linnehan serving as the muscle with his feet locked into a foot restraint at the end of the shuttle's robot arm, the old array was unfastened from the observatory by Grunsfeld and moved by Linnehan into a cargo carrier for the trip back to Earth.

Linnehan's movements are being handled by flight engineer Nancy Currie, who is on the shuttle's aft flight deck operating Columbia's 50-foot-long Canadarm.

The next step for the spacewalk, which is moving along ahead of schedule, is to change out some electronics on the telescope that will be required to accommodate the new solar array, which is also scheduled for installation by the spacewalkers this morning.

In general there have been no problems reported this morning with the exception of some paint flecks breaking loose from some of the handrails and floating free -- something that has been noted during previous spacewalks at Hubble and is not considered a threat to the crew.

You are invited to watch the spacewalk via our feed of NASA TV, available by the link above. We will post updates every couple of hours during the spacewalk, so fire up the coffee machine and enjoy the show. And if you have any questions or would just like to say hi, please feel free to drop me a note.

A brand new electricity-generating solar array has been mechanically attached to the side of the Hubble Space Telescope by spacewalking astronauts John Grunsfeld and Rick Linnehan.

Mating a series of electrical connections and an initial test of the new array is still ahead during this spacewalk, which has been underway for four hours.

With flight engineer Nancy Currie piloting the shuttle's robot arm, Linnehan rode at the end of the arm hanging onto the new array as it was guided into position on the telescope, where Grundfeld was floating ready to drive the nuts and bolts that would structurally attach the device.

Covered with solar cells made of gallium arsenide, the new array is about one-third the size of its original, weighs twice as much, yet generates more power -- enough to allow astronomers to operate all of Hubble's scientific instruments at the same time.

Stay tuned to this page for our next update in about two hours.

A new electricity-generating solar array installed this morning on the side of the Hubble Space Telescope is going through a so-called "aliveness test," which is performed after the wing-like panel is mechanically and electrically connected to the observatory.

The test checks the panel's ability to convert sunlight into electricity, feed that power into the observatory and move to track the sun as the telescope orbits the Earth. We should hear the results of that test shortly.

This morning's extravehicluar activity -- or EVA -- will be repeated early Tuesday when a second solar array will be replaced during the second of five planned spacewalks this week.

Meanwhile, today's spacewalk is wrapping up as astronauts John Grunsfeld and Rick Linnehan are finishing their assigned tasks. Some difficulties earlier with stowing the old solar array into a carrier in Columbia's cargo bay put the spacewalkers 15-20 minutes behind schedule.

We will update this page when the spacewalk officially concludes, an event expected within the hour.

Columbia astronauts John Grunsfeld and Rick Linnehan are safely back inside the shuttle's airlock after completing a seven-hour and one-minute spacewalk, which officially ended at 8:38 p.m. EST when the airlock started repressurizing.

The main task of today's spacewalk was to install a new solar array on the starboard side of the Hubble Space Telescope, and that task was peformed flawlessly. Electrical and mechanical checks of the new power wing are going well so far.

Hubble's port side solar array is to be replaced during a spacewalk that is scheduled to begin at 1:27 a.m. EST Tuesday. Participating in that spacewalk will be Jim Newman and Mike Massimino.

The only real difficulty encountered this morning came when the astronauts stowed the old array in its cargo bay carrier and one of four restraining devices would not fully engage at first. By the time that was solved the spacewalking pair had become slightly behind schedule.

The only other issue worth mentioning is that Grunsfeld's suit stopped sending data back to Mission Control about how well it was doing, so Grunsfeld had to make periodic reports on how the suit was doing and how much consumables were left. Engineers will continue to troubleshoot that problem in hopes of recovering that telemetry in time for Grunsfeld's next spacewalk early Wednesday.