This story was updated at 8:27 p.m. EDT.
The
International Space Station dodged a small piece of space junk Sunday leftover
from a spent Chinese rocket that broke apart in orbit nine years ago.
Mission
Control radioed the crew of the space shuttle Discovery, which is docked
at the station, to perform a small thruster maneuver that changed the
orientation of the space station, slowing it slightly and putting more
clearance between the $100 billion orbiting laboratory and approaching space
junk, NASA officials said.
NASA
officials said the chunk
of orbital debris is a small 4-inch (10-cm) piece of a Chinese satellite rocket
stage that launched in 1999 and broke apart in March 2000.
Space
station flight director Kwatsi Alibaruho said the space trash was going to fly
near the space station up to twice each orbit, the first time occurring Monday
about two hours into a spacewalk by astronauts. NASA traditionally does not
make orbital adjustments while astronauts are outside the station because of
the high forces the maneuvers put on the structure.
"Because of
our concerns about having to take action during a spacewalk, we preemptively adjusted
the orbit of the International Space Station and the space shuttle," Alibaruho
told reporters late Sunday.
Discovery
commander Lee Archambault
fired the shuttle's thrusters at about 4:00 p.m. EDT (2000 GMT) in a half-hour maneuver
to change the station's position as it flies through space. The orientation
places the shuttle in front of the station and is the same that will be used
when Discovery undocks on Wednesday. It should slow the station by about 0.1
feet per second due to atmospheric drag, NASA officials said.
"Over
several hours, this will lower the orbit very slightly, enough to avoid a piece
of orbital debris whose erratic orbit makes it a potential threat," NASA
officials said.
NASA
and its space station partners typically move the 1 million-pound (453,592 kg)
orbiting lab when a piece of debris is expected to fly within an imaginary box
that extends 15 miles (24 km) to either side of the outpost, which is longer
than a football field.
"Space
debris is becoming an ever-increasing challenge," Alibaruho said. "We've been
very fortunate, and also very diligent, about monitoring space debris."
Space debris traffic
The
Chinese debris is the third
piece of space junk to fly near the space station in two weeks. Mission
managers have said that while there seems to be recent uptick in space debris,
the events can ebb and flow like freeway traffic on Earth.
"I
think these types of things will come and go in seasons," Alibaruho said. "Right
now, we're going through a season where we've had a number of things that we've
had to dodge."
On
March 17, the remains of a Soviet-era military navigation satellite prompted
flew past the space station just before Discovery docked at the orbiting
laboratory. That debris was a small piece of the defunct Cosmos 1275 satellite,
but it zoomed past the space station at a far enough distance that no avoidance
maneuver was required.
That
was not the case for another piece of space trash that buzzed the space station
on March 12. That debris, a 5-inches (13-cm) wide piece of spent satellite
rocket motor, flew within 2.4 miles (4 km) of the space station at a clip of
about 19,800 mph (31,865 kph). The space station orbits the Earth at about
17,500 mph (28,163 kph).
Notice
of the March 12 debris event came too late for flight controllers to move the
space station. Instead, station commander Michael Fincke and his two crewmates had
to take shelter in their Russian-built Soyuz spacecraft, which doubles as a
lifeboat and ferry to and from the orbital laboratory.
Space
debris has been a growing threat for the International Space Station and other
satellites in orbit. On Feb. 10, an outdated Russian satellite collided with a
U.S. communications satellite in an
unprecedented crash that created two large clouds of debris.
NASA
said the collision increased the risk of a debris strike during a space shuttle
mission to the station by about 6 percent, or a 1-in-318 chance.
"There's a
lot of debris out there," Fincke said in a televised interview on Friday,
adding that space trash poses a risk to astronauts in space as well as the
satellites that aid life on Earth. "We need to be able to truly have a way to
dispose of our satellite when we're finished with them."
Discovery's
seven-astronaut crew had a half-day off at the space station Sunday morning as
the spaceflyers prepare for their third and last spacewalk on Monday. The
shuttle has passed the midpoint of its 13-day mission to replace a station
crewmember and deliver the outpost's final pair of U.S. solar wings, which were
unfurled on Friday.
Discovery
is due to undock from the space station on Wednesday.
SPACE.com
is providing continuous coverage of STS-119 with reporter Clara Moskowitz and
senior editor Tariq Malik in New York. Click here for mission
updates and SPACE.com's live NASA TV video feed.
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