STS-122 tank and SRBs to be mated Wed.

Solid rocket boosters stacked last week for STS-122.

Wednesday at 8 a.m. technicians will begin mating the external tank and solid rocket boosters for STS-122, on which Atlantis is scheduled to launch Dec. 6.

"It's an all day activity," said NASA spokesman George Diller.

Discovery on mission STS-120 is scheduled to launch on Oct. 23.

Processing for the Atlantis mission has been in High Bay Three, while Discovery was processed in High Bay Four last month. The second bay was returned to service after the massive doors were repaired because corrosion made them dangerous to open. Having two bays for shuttle processing means NASA has a better chance of completing the 14 scheduled missions before the program ends in 2010.

The solid rocket booster sections were stacked in the high bay last week.

"They're all mated," said Diller. "They're ready for the tank."

Foam on the tank brackets has been removed and replaced with lighter foam, a change made after a piece came loose during the launch of STS-118 and damaged the thermal tile beneath the shuttle.

Atlantis will carry the Columbus Laboratory, Europe's largest contribution to the construction of the International Space Station. It will support scientific and technological research in a microgravity environment.