This story was updated at 12:20 p.m. EDT.
The space shuttle Discovery dodged a mysterious piece of orbital trash Thursday as its astronaut crew prepared for a planned landing in Florida.
Shuttle commander Rick Sturckow and pilot Kevin Ford fired Discovery?s engines at 12:02 p.m. EDT (1605 GMT) for 14 seconds to move the spacecraft clear of the space junk and continue on with their landing attempt today.
The ?mystery orbital debris,? as Mission Control called it, apparently came free from the shuttle or the International Space Station while both vehicles were linked during a spacewalk on Saturday. NASA engineers do not know what the object is or its size, but it has been creeping ever closer to Discovery since the shuttle fired its engines to leave the station?s orbital neighborhood Tuesday.
At 12:55 p.m. EDT (1655 GMT), the debris was expected to fly within a safety perimeter box that extends out 25 miles (40 km) around Discovery and 2 miles (3 km) above and below the shuttle.
?Based on the latest tracking data, the object will move in and out of that box over the course of 11 consecutive orbits,? said NASA commentator Pat Ryan. ?The two objects [are] in essentially the same orbit, but with different velocities.?
Discovery?s debris-dodging maneuver will not impact NASA?s plan to try and land the shuttle at the Kennedy Space Center in Florida today, Mission Control said. The shuttle is due to touch down at 7:05 p.m. EDT (2305 GMT), but could also try for an 8:42 p.m. EDT (0042 Sept. 11 GMT) opportunity depending on weather conditions.
Thunderstorms near the shuttle runway could keep Discovery and its seven-astronaut crew in orbit an extra day. NASA could also activate a backup runway in California as early as Friday in order to bring the shuttle home. The shuttle blasted off late Aug. 28.
Space debris has dogged Discovery?s mission to the International Space Station.
A piece of Chinese satellite debris was due to pass by the space station twice early Wednesday, but never came anywhere near the orbiting laboratory. Last week, a massive chunk of a 3-year-old European rocket buzzed the orbital outpost and linked shuttle, zipping past about 1.3 miles (3 km) ahead of the station, but it too posed zero risk of impact, Mission Control said.
Discovery is returning to Earth to wrap up a 13-day cargo run to the space station. The astronauts performed three spacewalks, replaced one member of the station?s crew and delivered tons of supplies, science gear and a treadmill named after TV comedian Stephen Colbert.
The shuttle is bringing home NASA astronaut Tim Kopra, who is ending a nearly two-month mission to the space station. He was replaced by astronaut Nicole Stott during Discovery?s flight.
Discovery is also returning Buzz Lightyear, a 12-inch Disney toy, to Earth to wrap up his own 15-month space mission. Buzz launched to the station in May 2008 as part of an educational campaign and will receive a hero?s welcome at Walt Disney World in Florida - including a tickertape parade - after returning to Earth.
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- SPACE.com Video Show - The ISS: Foothold on Forever
SPACE.com is providing complete coverage of Discovery's STS-128 mission to the International Space Station with Managing Editor Tariq Malik and Staff Writer Clara Moskowitz in New York. Click here for shuttle mission updates and a link to NASA TV.