A piece of
space junk orbiting Earth has forced NASA to tweak upcoming plans for the Friday
departure of Japan's first cargo ship to the International Space Station.
The debris,
a wayward chunk of an old Russian satellite, poses no risk to the space
station, but could be a threat to the H-2 Transfer Vehicle, an unmanned
Japanese freighter making its maiden flight, after it departs Friday.
Japan's
space agency launched the cargo ship last month and planned to undock it tomorrow
at about 12:05 p.m. EDT (1605 GMT). But the Russian piece
of space debris is expected to pass through the station's neighborhood
around that time, so NASA opted to keep the Japanese spaceship attached to the
orbiting lab for one extra orbit. It will now undock at around 1:30 p.m. EDT
(1730 GMT).
The space
station will not have to fire its thrusters to dodge the space junk. Delaying
the HTV-1's departure will ensure that the unmanned spacecraft will be safe
after it leaves the station and enters a different orbit, NASA officials said.
NASA typically
moves the space station if the odds of a space debris impact are within a
1-in-10,000 chance. The agency also likes to keep a box-like buffer around the
station free of any debris. That safety zone extends about 15 miles (25 km)
around the space station, as well as about a half-mile (0.75 km) above and below
it. The station flies in an orbit about 220 miles (354 km) above Earth.
The Russian
satellite debris will not encroach within that perimeter, NASA spokesperson
Kelly Humphries told SPACE.com.
"They
tracked it for a few days and determined it was going to be outside what we
call the pizza box, and that the station will be safe," he said. "They just
wanted to give HTV the same courtesy."
Space
debris has been a growing threat for satellites and crewed spacecraft in orbit.
Earlier this year, two
communications satellites collided to create two vast clouds of space junk
orbiting Earth. China also added to the debris mix in 2007 by intentionally
destroying a satellite in orbit during an anti-satellite test.
Some
experts have said the more than 20,000 objects being tracked by various
agencies today already represent a serious threat
to satellites and other spacecraft. They have called for a renewed push to
limit the amount of junk from new satellites and develop clean-up measures for
the orbits near Earth.
Japan's
HTV-1 cargo ship launched to the space station on Sept. 10 and arrived on Sept.
17 after a smooth shakedown cruise. The vessel is the latest in a series of disposable
unmanned international spacecraft to deliver supplies to the space station.
The
spacecraft is due to undock Friday with nearly 1,600 pounds (728 kg) of trash
and then plunge into the Earth's atmosphere on Sunday to be intentionally
destroyed over the Pacific Ocean.
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