A small
piece of space junk will fly uncomfortably close to the International Space
Station late Friday and may force astronauts aboard the outpost to take shelter
in their Russian lifeboats.
NASA's
Mission Control radioed the six astronauts on the station earlier today to
alert them of the approaching
space junk, which will fly within 1,640 feet (500 meters) of the orbiting
laboratory Friday night at 10:48 EST (0348 Saturday GMT).
Sending the
astronauts into their Soyuz lifeboats would be a precaution only, NASA
officials said. Currently, the space junk poses no threat to the station or its
crew, they added.
"It's pretty unusual," said Kirk Shireman, NASA's deputy
station program manager, said of the shelter plan in an interview. "I wouldn't
be surprised if the need to do it for this [debris event] goes away."
The object
is likely very small because it is difficult to
track, NASA spokesperson Rob Navias told SPACE.com. News of its close
approach to the station came too late to steer the massive orbiting laboratory
clear using its Russian thrusters.
"We don't
know what it is or the size," Navias said.
Station
astronauts will find out before the end of the day today whether they'll have
to sleep inside the two Soyuz spacecraft that serve as ferries to and from the
station, as well as lifeboats in an emergency escape. Another option is to wake
up before the space junk zooms by and then take shelter for a short while until
the threat has passed, Navias said.
The station
crew is due to go to sleep at about 4:30 p.m. EST (2130 GMT).
This is not
the first time a piece of wayward space junk has come close enough to send
astronauts into their Russian lifeboats.
A close
pass by an old rocket engine remnant sent three station astronauts into
their Soyuz spacecraft earlier this year in March. Since then, however, the
space station's crew size has doubled to six astronauts, so two Soyuz vehicles
are currently docked to the station.
NASA also delayed
the departure of a Japanese cargo ship from the space station last week
because of a space debris threat.
The space
station is currently home to two Americans, two Russians, a Canadian and
Belgian astronaut Frank De Winne of the European Space Agency, who commands the
team's Expedition 21 mission.
NASA typically
prefers to move the space station when the odds of a space debris impact are
within a 1-in-10,000 chance. Astronauts take shelter when debris is expected to
fly within a so-called "red zone" and the space station doesn't have time to
dodge, Shireman told SPACE.com
There is
also a box-like buffer around the station that mission managers prefer to keep
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 at a speed of
about 17,500 mph (28,163 kph).
But a
debris avoidance maneuver – as dodging space junk is known at NASA – can take
days to plan. The space station's Mission Control team did not have that time
because of the short lead time, Navias said.
Space
debris has been a growing threat for manned spacecraft and other satellites in
orbit today.
The
collision between two
communications satellites earlier this year brought the issue to the
forefront. It, as well as China's intentional destruction of a satellite during
a 2007 anti-satellite test, have sparked a renewed push to better track, and
possibly reduce, the more than 20,000 pieces of space junk currently watched by
various agencies.
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