Shuttle Columbia touches down at the Kennedy Space Center following its highly successful Hubble service call. Photo: NASA TV/Spaceflight Now

The space shuttle Columbia glided to a smooth touchdown today on runway 33 at the Kennedy Space Center to close out a surprisingly successful five-spacewalk mission to overhaul and upgrade the Hubble Space Telescope.

With commander Scott Altman and pilot Duane Carey at the controls, NASA's oldest space shuttle dropped out of a moonless night sky and into the glare of powerful xenon spotlights after an hourlong plunge back to Earth. Main gear touchdown occurred at 4:31:52 a.m.

"Houston, Columbia, wheels stopped KSC," Altman, a former "Top Gun" Navy fighter pilot, radioed after the spaceplane rolled to a halt.

"Columbia, Houston, we copy wheels stopped," replied astronaut Mark Polansky from mission control. "Welcome back and we'd like to congratulate you all on a very successful mission servicing the Hubble Space Telescope. We have no post-landing deltas."

Today's landing capped a 4-million-mile voyage spanning 11 days and 165 complete orbits since blastoff March 1 from nearby pad 39A. This was the 19th night landing in shuttle history, the 14th night landing at KSC and the 58th landing overall at the Florida spaceport. Mission duration from launch to main gear touchdown was 10 days 22 hours nine minutes and 51 seconds. It was Columbia's 27th flight.

"Columbia had a great entry," said Linda Ham, a senior shuttle manager at the Johnson Space Center. "Overall, Columbia's performance really was exceptional."

But two issues will require post-landing repairs that could affect Columbia's next flight, currently targeted for launch July 11. Blockage in a Freon coolant loop must be located and fixed and one of the shuttle's steering jets failed in orbit and will need to be replaced. Ham said it may be possible to hold the July 11 launch date, but only if engineers quickly locate the Freon line blockage and only if it's in an area that doesn't require engineers to drain both of the shuttle's coolant loops.

Altman, Carey, flight engineer Nancy Currie and spacewalkers John Grunsfeld, Richard Linnehan, James Newman and Michael Massimino plan to spend the day at the Kennedy Space Center before flying back to Houston on Wednesday.

"And Houston, we just want to say fantastic job with us all the way through the mission," Altman radioed mission control before leaving the shuttle. "You guys did a super job, brought us a beautiful night and it's great to be back here at Kennedy Space Center after this incredible experience at Hubble. So thanks much".

During five back-to-back spacewalks last Monday through Friday, Grunsfeld and company rejuvenated the Hubble Space Telescope's power system, installed a powerful new camera and an experimental refrigerator needed to revive a now dormant infrared camera-spectrometer.

The spacewalks were the most complex in shuttle history and the crew set a new single-flight record for cumulative spacewalk time: 35 hours and 55 minutes. During 18 spacewalks over four Hubble servicing missions to date, 14 astronauts have now logged 129 hours and 10 minutes servicing NASA's flagship science satellite.

"The best word that I can think of to describe this servicing mission is awesome, like in 'totally awesome, dude,'" said Preston Burch, Hubble program manager at the Goddard Space Flight Center. "The Hubble servicing missions in my view just seem to get better and better. This is by far our best servicing mission to date.

"This mission was crammed full of tough, challenging work and many people on this mission privately didn't think that we would be able to accomplish everything we set out in our plan," he said.

"This mission required an incredible amount of dedication and hard work by a huge team of people at the Johnson Space Center, the Kennedy Space Center, the Goddard Space Flight Center, private industrty and academia. And I especially wanted to thank all of them and I especially want to tank our seven crew members on the Columbia who were just absolutely incredible in how they pulled this off."

Next up for NASA: Launch of the shuttle Atlantis April 4 on a mission to the international space station. The goal of the flight is installation of the S0 truss, a huge open framework backbone that eventually will anchor the station's huge solar arrays.

Engineers at the Kennedy Space Center plan to move Atlantis to launch pad 39B later this morning. But recent problems with the space station's robot arm, which is required to attach the S0 truss to the top of the Destiny laboratory module, could cause a delay.

Engineers at Goddard, meanwhile, are continuing around-the-clock work to re-activate and calibrate Hubble's instruments and subsystems, on track to resume enhanced science observations.

It will take several weeks of fine tuning before the first post-servicing images are released but so far, tests and checkout operations are proceeding smoothly with no problems of any significance.

In another welcome, if expected, bit of good news, engineers report Hubble's new solar arrays, smaller and much stiffer than the panels they replaced, are proving much less susceptible to minute temperature-induced flexing as the observatory passes into and out of Earth's shadow.

Such flexing by the old arrays caused minor but noticeable perturbations, prompting development of elaborate software routines to maintain precision orientation control during astronomical observations. The new arrays are not prone to such flexing. They generate 20 percent more power than the old panels and their smaller size generates less atmospheric drag.

"Hubble has really opened our eyes to what the universe is made of, its structure, and it has helped us learn how little we know about the universe," Grunsfeld said from orbit.

"It's helped us explore the beauty of the universe in a way that we've never been able to before in terms that people can see. ... When we look back, maybe 30, 40 or 50 years from now, I think we'll see Hubble as the most productive scientific instrument in human history. It's had that big an impact on people's lives."