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A close one for the space station

NASA illustration
  Click for video: NBC
  News' Tom Costello
  reports on the space
  station's close call.

The international space station's three crew members climbed into their Soyuz lifeboat as a "precautionary measure" while a piece of space junk passed by today, NASA said. The space agency said the debris from a spent satellite rocket motor zipped past, apparently without causing damage, and the crew was given the all-clear to return to the station and resume normal operations.

NASA spokesman Bill Jeffs said this sort of maneuver is not unprecedented - it's happened at least once before. Usually, NASA has enough advance warning to move the station well out of the way. In this case, however, military debris-trackers alerted NASA on Wednesday night, too late to plan an avoidance maneuver.

Space agency spokesmen said this afternoon that the debris was about 5 inches (12.7 centimeters) in size, which would be larger than the initial estimates of 0.35 inches (9 millimeters). The space junk, said to be from a PAM-D, or payload assist motor, was projected to pass about 4.5 kilometers (2.8 miles) from the station at 12:39 p.m. ET, Jeffs said.

That was close enough to cause concern: Another agency spokesman, Josh Byerly, told me that a collision alert is raised anytime an object is projected to come within an imaginary "pizza box" around the station, measuring 0.75 kilometers above and below the station and 25 kilometers on each side (0.47 miles up and down, by 15.6 by 15.6 miles).

That's why the crew was told to put the station into unmanned mode, get into their Russian-built Soyuz capsule and wait. If the debris had struck the station and breached the hull, the crew might have had to fly the Soyuz back down to Earth and leave the multibillion-dollar orbiting outpost under remote control.

The three crew members - station commander Mike Fincke and flight engineer Sandra Magnus from NASA, as well as Russian cosmonaut Yuri Lonchakov - waited for a tense 10 minutes, looking out the Soyuz windows. "We didn't see anything, of course," Fincke said later. "We were wondering how close we were."

Orbital debris has been a big issue for NASA and the military these days, in part due to last month's collision of a Russian military satellite and an Iridium telecommunications satellite that created hundreds of pieces of junk. The space agency also noted recently that the space-junk factor has raised the estimated risk for an upcoming shuttle mission to service the Hubble Space Telescope - from a 1-in-300 chance of catastrophe to a 1-in-185 chance.

A 5-inch-wide piece of metal might not sound like much, but it can be a big deal when it's traveling 18,000 miles (28,800 kilometers) per hour. Critical parts of the station have been shielded to withstand the impact of objects on the order of a centimeter wide, and ground controllers try to make sure that the station can be moved far away from bigger objects.

Over at Spaceflight Now, Bill Harwood points out that "a 0.4-inch-wide sphere of aluminum moving at orbital speeds packs the same punch as a 400-pound safe moving at 60 mph."

Check out this archived story and this FAQ file from NASA for more about our orbital junkyard and the problems it's causing.

Update for 3:57 p.m. ET: NASA's Josh Byerly told me that the space station's crew has taken refuge in the Soyuz as many as five times before today due to concerns about passing space debris. You can listen to highlights from today's conversation between station crew members and Russian Mission Control by clicking through to this audio clip.

Update for 4:21 p.m. ET: Byerly has corrected the earlier estimate of the object's size. He said in an e-mail that the earlier, smaller number "was actually the radar cross section number, which equates to the larger size." The reference to the size has been revised above.

Update for 10:26 p.m. ET: The Associated Press report about the close call stresses the fact that there's much more junk where today's piece came from. "It's yet another warning shot that we really have to do something about space debris now. We have to do something on an international level," Harvard astrophysicist Jonathan McDowell told AP. Just yesterday, The Wall Street Journal delved into several heavy-duty methods for getting rid of space junk, including nets, magnets, lasers and rocket-powered water guns.

Earlier versions had the time for closest approach slightly wrong, and misstated one of the dimensions for the "pizza box" - which is an occupational hazard when a person has clumsy fingers and is trying to juggle a Twitter feed as well. (Tip o' the Log to Tom Sowa.)