Space Shuttle Discovery is poised to wrap up the long 15-day STS-120 mission with a landing just after 1 p.m. ET Wednesday, capping a challenging spacewalk in which physician- astronaut Scott Parazynski rode the end of an extra-long boom to repair a torn solar array. (For NASA assessment of mission, please see separate story.)

The mission also saw the shuttle bring the International Space Station (ISS) a major new addition, the Italian-built U.S. Node 2 Module "Harmony" that expands living space on the artificial moon. The module also will serve as a connecting area to future laboratories to be added to the ISS on later missions.

Discovery heads into reentry Wednesday after meticulous and repeated inspections found no deterioration of three problem thermal protection heat tiles on the leading edge of a wing on the orbiter vehicle.

Coatings on the reinforced carbon-carbon (RCC) tiles showed cracking at the edges, and some engineers had recommended replacing the tiles before Discovery launched from Kennedy Space Center (KSC) Pad 39A Oct. 23.

But exhaustive inspections of the tiles after Discovery attained orbit showed no further damage, confirming that the decision to launch the shuttle was correct. So mission control gave Discovery a clean go for reentry. Problems with a damaged heat-tile system led to the 2003 loss of Space Shuttle Columbia and its crew during reentry, so NASA is highly sensitive to heat-tile shortcomings.

Because of the solar array tear, NASA had to abandon plans for a spacewalk to test in-orbit thermal tile repair techniques on intentionally damaged test tiles, and also had to forego a planned extravehicular activity to check a problem with metal shavings on a movable space station joint.

That torn solar array is a critical element in plans to expand the space station, because it is needed to generate sufficient electricity to power those future laboratories.

If the tear hadn’t been fixed, it might have grown larger and meant the loss of the solar array as a power generator.

Parazynski, in surgeon-like fashion, used wire clips that work much like cufflinks to stitch the solar array wound back together.

In doing so, he had to ride on a boom extension that placed him about 100 feet out, a long way in the event of a problem with his space suit, and he also had to avoid touching the solar array and its powerful electrical current.

After he finished the job, the solar array — which had torn on a wire before it reached 80 percent deployment — was able to be deployed to its full 100 percent extension, so that it can generate about 97 percent of expected power for the ISS.

Yesterday, an emotional farewell ceremony in orbit was followed by the STS-120 space shuttle crew members entering the shuttle, leaving behind the Expedition 16 space station crew members on the ISS, and hatches were closed between the shuttle and space station. Finally, undocking of the shuttle from the space station occurred early this morning.

Discovery then began a fly-around to gain video of the newly-expanded space station. As well, there are the usual final checks of heat tiles on the shuttle before it braves the searing heat of reentry en route to landing at KSC.

The STS-120 crew installed Harmony Oct. 26 and conducted a total four spacewalks during the shuttle stay at the station.

During the third spacewalk, the crew installed the P6 truss and solar array pair in its permanent location outboard of the port truss. The fourth spacewalk was changed during the mission so that the crew could repair that torn solar array on the P6 truss.

Discovery also delivered a new station crew member, Flight Engineer Daniel Tani. He replaced astronaut Clayton Anderson.

Anderson arrived at the station in June with STS-117.

Other crew members include retired Air Force Col. Pamela A. Melroy, who commands the STS-120 shuttle mission. Melroy, a veteran shuttle pilot, is the second woman to command a shuttle. Marine Corps Col. George D. Zamka serves as pilot. The flight’s mission specialists are Parazynski, Army Col. Douglas H. Wheelock, who joined in the tear-fixing spacewalk, Stephanie D. Wilson and Paolo A. Nespoli, a European Space Agency astronaut from Italy. Zamka, Wheelock and Nespoli are making their first spaceflights.

Expedition 15/16 Flight Engineer Clayton Anderson is returning to Earth from the space station aboard Discovery. His replacement, Tani, will return on Space Shuttle Atlantis on the STS-122 Mission that is slated to launch from KSC Dec. 6.