Engineers are studying the potential impact of a crack found in a cue ball-sized bearing inside a liquid oxygen feed line aboard the shuttle Discovery. The crack was discovered during routine inspections as part of on-going maintenance and modifications every orbiter periodically goes through. At issue is what caused the crack, whether it represents a safety threat and whether or not it poses any sort of fleet-wide issue.

As of this writing, engineers are optimistic it's not a generic problem. But shuttle program manager Ronald Dittemore has ordered a team of engineers to investigate the matter and to examine a similar bearing in the shuttle Atlantis' oxygen feed line to see if any problems are present.

NASA currently has its collective sights set on launching the shuttle Columbia Jan. 16 on a Spacehab microgravity research mission featuring the first Israeli astronaut. There are no plans at present to attempt any sort of inspection of the bearing aboard Columbia, which sources say would be difficult with the orbiter in the vertical orientation at launch pad 39A. But that could change depending on how the investigation plays out.

The 2.25-inch-wide bearing in question is part of a system that allows a big 17-inch-wide feed line bellows inside the shuttle's engine compartment to flex slightly while maintaining its structural integrity. Inside the propellant line, two sets of struts forming interlocking three-legged pyramids are hooked together under compression. The bearing in question, located upstream of the point where the main oxygen line branches apart to serve each main engine, serves as a common apex of sorts for the interlocking struts.

During an inspection of this bearing in the liquid oxygen feed line aboard Discovery, engineers noticed a "discernible crack," one official said. One concern is the possibility that a piece of metal could break off and get sucked into one of the shuttle's three main engines during ascent.

As of this writing, any speculation about the potential impact of this issue is just that - speculation - but NASA managers are hopeful the upcoming inspections will show the bearing problem is isolated to Discovery.

Last summer, during routine post-flight inspections of Atlantis, engineers discovered a small crack in a liner inside the 12-inch-wide liquid hydrogen feed line leading to main engine No. 1. Two more cracks in the same flow liner were found the next day.

Similar cracks then were found aboard Discovery, Columbia and Endeavour, prompting Dittemore to ground the fleet until corrective action could be taken. Shuttle flights resumed in October after a three-month hiatus.

Engineers say the current issue is unrelated to the earlier flow liner cracks and may be of no consequence when all is said and done. Stay tuned.