Boeing technicians work on Columbia as seen in top photo. The bottom view shows the ship's stripped nose. Photos: Spaceflight Now

More than 350 Boeing workers, some of whom built Columbia in the late 1970s, are giving the stubby winged spaceplane a complete physical and installing improved systems.

The shuttle was ferried atop a modified Boeing 747 from its homeport at Kennedy Space Center in Florida to Palmdale last September. Columbia made its most recent flight -- its 26th mission -- in July, placing NASA's Chandra X-ray Observatory in space.

Over the past several months, the craft's insides have been gutted, removing everything from power generators to storage lockers to allow technicians to perform 400 separate inspections of the shuttle's structure. All the shuttles are built to fly 100 times, meaning Columbia has only lived a quarter of its life.

The stresses of being propelled from Earth into orbit, going from zero to 17,000 miles per hour in 8 1/2 minutes, plus working in the harsh environment of space causes NASA to order shuttle checkups every couple of years.

On this Palmdale visit -- Columbia's fourth since rolling off the assembly line in March 1979 -- workers are looking for signs of wear and tear, corrosion and wiring defects.

A Boeing worker points out an area where corrosion has been removed from the shuttle's body flap. Photo: Spaceflight Now

The man in charge at Palmdale, Boeing's Al Hoffman, says Columbia looks pretty good. "She is in fine shape with no real surprises found so far."

Some corrosion was discovered around the ship's body flap, which is located on the tail below the three main engines. The damage probably was caused by rain as Columbia sat on its launch pad. The flap has been removed and cleaned.

Still, inspectors note, the corrosion was not as extensive as damage found on some of Columbia's younger sisterships.