Perseid Meteor Shower Poses Minimal Risk to Spacewalking Astronauts

The Perseid meteor shower peaks tonight, promising dazzling fireball displays to lucky skywatchers, but the cosmic rain of space rocks hasn?t endangered space station astronauts during their spacewalk repairs this week, a NASA scientist says. In fact, the meteor shower may give the astronauts a show too.

Astronomer Bill Cooke, a meteor expert with NASA's Meteoroid Environments Office, said the Perseid meteor shower adds a small amount of risk to astronauts on spacewalks (about 15 percent), but the chances of being hit by a tiny meteoroid from the shower are slim.

"The risk is still below the risk posed by orbital debris and other factors," Cooke told SPACE.com from the Marshall Space Flight Center in Huntsville, Ala.

Currently, there is a 1-in-300 chance of a piece of orbital debris damaging the space station or hitting a spacewalking astronaut. Compared to that, the slight risk increase from the Perseids is negligible.

A meteoroid about 1 millimeter in size is large enough to damage an astronaut's spacesuit during a spacewalk, Cooke said. But NASA spacewalk planners take the micrometeorite environment into account when scheduling excursions, he added.

There are six astronauts living aboard the International Space Station; three Americans and three Russians.

The crew is in the middle of a challenging set of four spacewalks to repair the space station's cooling system. One of two vital ammonia coolant pumps failed July 31 and station astronauts are tackling the tricky job of replacing the oven-sized part with a spare. They performed spacewalks on Saturday and Wednesday, with the next one set for Monday.

If the space station astronauts are lucky, they may be able to see meteors from above as they soar 220 miles (354 km) above the Earth's night side. In the past, astronauts have been able to record video of meteors from space during shuttle missions.

"You can definitely see meteors, and it's kind of cool," Cooke said.

This sky map shows where to look to see the meteor shower. Skywatchers on Earth can use SPACE.com's planet alignment map to find and identify planets that are appearing together at the same time as the meteor shower.

During the Perseid meteor shower, the Earth is pelted by remains of the Comet Swift-Tuttle as the planet passes close to the comet's orbit. Material left behind by the comet rams into the Earth's atmosphere during the pass at about 37 miles per second (60 km/second), creating an annual show of "shooting stars" every mid-August.

One of the reasons the Perseids don't post a major risk to astronauts on the space station is because, astronomically speaking, astronauts are rather small, Cooke said.

"When you look up in the sky, you see about 10,000 square-kilometers," Cooke said. "An astronaut's surface area is about 1 square-meter, he's not a very big target."

The space station, too, is small compared to the entire night sky, Cooke added. Still, the $100 billion International Space Station is the largest spacecraft every built in space and has a main truss as long as a football field. It can easily outshine Venus on clear nights and be seen by the unaided eye.

Cooke plans to stay up all night tonight to observe the peak of the Perseid meteor shower. The Marshall Space Flight Center is planning to stream live views and from its all-sky cameras in Alabama and Georgia via the Internet, he added.

"It's NASA's first up-all-night," he said.

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• Galleries: Perseid Meteor Photos in 2005 and 2006

NASA's live Perseids meteor shower show begins Thursday night at 11 p.m. ET and runs through 5 a.m. ET Friday: http://www.nasa.gov/connect/chat/perseids_2010.html