NASA is investigating whether repairs to a small crack in the foam on Shuttle Discovery's (search) fuel tank may have caused a 1-pound section of the insulation to break off during liftoff, officials said late Friday.

The shallow crack — just six-tenths of an inch long and two-tenths of an inch wide — was sanded away at the Louisiana manufacturing plant before the tank was shipped to Cape Canaveral, Fla. No new foam was applied to the spot.

It's a common repair procedure, NASA (search) officials said.

What's intriguing, officials said, is that the repair was made to the approximate area where the big chunk of foam came loose during Discovery's launch on July 26. They cautioned, however, that there is no evidence yet that the repair contributed to the foam loss.

The external fuel tank was redesigned following the 2003 Columbia tragedy, but no improvements were made to the area where the foam came loose. Lockheed Martin Corp. (search) built the tank at its Michoud Assembly Facility in New Orleans.

Unlike with Columbia, which was smacked in the wing by foam that broke off during liftoff, this large chunk of foam missed Discovery. Nonetheless, NASA has suspended all future space shuttle flights until the problem is resolved.

Among the many theories being investigated, besides the crack: whether a mistake was made in the manual spraying of the foam, whether tequent Russian supply ships for garbage disposal.

The shuttle's latest grounding could mean another trash pileup.

Discovery took up some 3,000 pounds of badly needed station supplies like prepackaged meals and spare parts in the massive canister. Once it was attached to the space station and emptied, it was filled to capacity with all the discarded station objects and placed back aboard the shuttle, with the help of a robot arm.

Everything had to be bagged or tied down just so for the shaky ride down through the atmosphere on Monday.

A call from Mission Control went unanswered for a few minutes as the astronauts stepped through the tedious job. "Sorry to ignore you," astronaut Stephen Robinson radioed as the crew secured items in large white bags. "We all have our heads down in bags."

The shuttle astronauts also put away the inspection boom that they used during their 13-day mission to survey Discovery's thermal skin, in a hunt for any launch damage.