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How to Dodge a Space Bullet in Three (Not So Easy) Steps How to Dodge a Space Bullet in Three (Not So Easy) Steps

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How to Dodge a Space Bullet in Three (Not So Easy) Steps

Avoiding superfast space trash is part of life on the International Space Station.

photo of Alex Brown
April 3, 2014

How NASA Avoids Space Junk

Getting to space isn't easy. Dodging bullets once you get there is even harder.

Thanks to carelessness and satellite collisions, Earth's atmosphere is littered with a half-million or so pieces of debris. And they're all traveling 17,500 miles per hour—roughly 10 times the speed of a bullet. Even a golf ball at that speed could take out a satellite system.

 

The dangers of space debris are not lost on NASA, particularly as it attempts to protect the International Space Station and the astronauts who live inside it. In fact, just this month NASA had to move the International Space Station to avoid a potential collision. Here's how NASA does it:

Step 1. Track the debris.

This actually isn't NASA's job. Most debris tracking is left to the Air Force. With its Space Surveillance Network, the Air Force follows roughly 15,000 pieces of whizzing space trash. The network is made up of 30 radar and telescope fixtures that keep a running satellite catalog.

Each day, the Air Force conducts roughly 400,000 spot checks to confirm objects are in the orbit they're predicted to be. How important is it to know where debris is? According to NASA, even paint flecks traveling at orbital speeds can damage a spaceship.

Tracking has become even more difficult—and crucial—since last year. Sequestration forced the Air Force to shut down the Space Fence, a series of radars that had accounted for 40 percent of the network's observations.

The Space Fence had served as a trip wire, passively watching for new activity rather than actively tracking known objects. Without it, it becomes harder to see collisions than can lead to larger debris fields. A new, better-equipped Space Fence is scheduled to be deployed in 2018. For now, NASA maintains that current tracking is up to the challenge of keeping its ships safe.

Step 2. Assess the risks.

Every eight hours, trackers check the orbit path of the space station against known debris that might cause danger. If objects will pass within a certain proximity, they alert NASA. In the first half of 2013, for example, 67 such warnings were sent.

Once warned, NASA starts crunching the numbers. Scientists try to determine if the object will pass within a so-called "pizza box." That's the area about a mile above and below the space station, extending about 15 miles to each side.

If debris might enter that area, NASA and its Russian partners start to come up with a plan. If collision risk is at least 1 in 100,000, the space station will make a precautionary move unless it interferes with its mission. If the risk reaches 1 in 10,000, a move becomes mandatory.

Planning a move requires about 30 hours, NASA says. Movements generally take place several hours before debris gets close.

Step 3. Get out of the way.

This can be achieved in several ways. Gyroscopes on board the ISS can reorient where the station faces within its orbit. Thrusters can move it into a different orbit. In addition, NASA can use the propellant systems of spacecraft attached to the station to change its location.

To calculate the proper thrust, NASA keeps precise track of the station's mass, depending on which vehicles are docked. Before a maneuver, NASA does a double check with debris trackers to make sure the movement won't intersect ISS with a separate piece of space trash.

In the rare case debris is discovered at the last second, mission control moves into the Predetermined Debris Avoidance Maneuver, which moves ISS to a different location at a half-meter per second. If that's not an option, the crew takes shelter in the Soyuz escape craft.

Movements are conducted from the ground; astronauts don't hit a throttle to relocate their home. In fact, during the debris maneuver earlier this month, the crew was asleep as ground engineers moved them to safety.

NASA says there wasn't likely to be an impact, but the seven-minute maneuver conducted March 16 provided a "healthy margin of clearance" from the debris of a Russian satellite launched in 1979.

Engineers used thrusters from Russia's Progress 54 spacecraft that was docked with the ISS, raising the station's altitude by about half a mile. The debris passed safely with plenty of room to spare, NASA said.

What next? Back to tracking, waiting for the next space bullet with astronauts in its sights—and getting out of the way before it's too late.

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