As of Wednesday night, the debris was expected to pass within two miles of the outpost Friday, said John McCullough, chief of NASA's flight director office.
That's five miles closer than earlier projections, but it's still "looking very positive" that the shuttle and station will not have to dodge the junk. That's because with every passing hour, there's more accuracy on the precise location of the spacecraft and debris, McCullough said.
Experts will continue to track the debris - part of a 3-year-old Ariane 5 rocket - to make sure it stays at a safe distance. Pieces of uncontrolled space junk sometimes stray from their orbit, however, and that is the concern. The object's oval-shaped orbit - stretching as far out as 20,000 miles - made it especially difficult to monitor.
Experts estimate that the piece of junk - part of a booster that was used to deploy a satellite - has about 200 square feet of surface area. Its exact dimensions are unknown.
The late-breaking news did not affect the work of the two crews aboard the complex. They got ready for Thursday evening's spacewalk, moved more cargo into the space station and even installed some of the new big-ticket items, including a sleeping compartment.
Shuttle astronaut Jose Hernandez, a Mexican-American who grew up in a migrant worker family, also took time out for several TV interviews and discussed his Catholic faith.
When asked in Spanish if being surrounded by all that science and technology diminished his faith, Hernandez replied that on the contrary, seeing Earth and all the stars from on high confirms his belief that all this cannot possibly be by chance and that there is a greater plan with a supernatural power.
"You can see with your eyes how marvelous our world is, our atmosphere is," he said.
Hernandez said he always carries with him, even now, his scapular and crucifix, which received the blessing of his parish priest.
The astronaut sent greetings to Mexican President Felipe Calderon, who happens to be from his parents' home state of Michoacan, as well as his Aunt Rosa, who promised to have some good meat tacos waiting for him. Friends, meanwhile, promised "a good mole" sauce on his next visit to Mexico.
Hernandez said he bicycles and runs every day, even in space. "That way, I can eat all the Mexican tacos and cornitas and mole," he said.
If Mission Control determines the shuttle-station complex needs to dodge the orbiting debris, that move into a higher orbit would not happen until early Friday, just after Thursday night's spacewalk. The joined spacecraft currently are flying about 220 miles above the planet.
A final decision was not expected until late Thursday.
The astronauts performed the first of three planned spacewalks Tuesday, removing an old ammonia tank from the space station. On Thursday, two spacewalkers will install a new, fully loaded tank to replenish the cooling system of the outpost.
Discovery will remain at the space station until Tuesday.
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