Quick Study: What is space junk?

Space debris poses a threat to spacecraft, scientists say.
Space debris poses a threat to spacecraft, scientists say.
Image: NASA.
At some point, every space inhabited by humans fills with junk -- the garage, the coat closet and the top kitchen drawer. Even outer space.

    And while the amount of debris floating in orbit around the Earth is not a problem that troubles most of us, it is a global issue, according to the European Space Agency, or ESA, which recently held a press conference on the issue. 
     But what is space debris or "space junk" and how did it get there? Here is a compressed account, along with sources for further study.

What is it? First, there is “natural” space junk -- meteoroids in orbit around the sun. But space junk is also man-made debris in orbit around the Earth. Examples of space junk might include a spent piece of rocket or a defunct satellite. Humans have been putting satellites into space for 60 years. Over time, some of the junk has fallen back to Earth -- but not all of it.

How much space junk is there?  An article on NASA’s website notes that more than 500,000 pieces of space debris orbit Earth. The ESA estimates that there are approximately 29,000 pieces larger than 10 centimeters (about 4 inches). While a 4-inch object may not sound threatening, consider that it is not simply free floating, but traveling at estimated speeds of 17,500 mph.

How did it get there? The short answer is that various military and space programs worldwide put it there. About a quarter -- 24 percent -- of space junk comes from satellites. Less than a third of those are currently operational, according to ESA. And an additional 18 percent are spent upper stages of rockets and “mission-related objects” such as launch adapters.
     An anti-satellite test 10 years ago also added to the problem. On Jan. 11, 2007, the Chinese military destroyed the Fengyun-1C weather satellite to test an anti-satellite system. That incident increased the trackable space objects by 25 percent, according to the ESA.

Why is this a problem: Scientists are concerned about the debris, especially as manned spaceflights continue. And while we don't think about it, satellites are an integral part of daily life. They are used in space science, Earth observation, meteorology, climate research, telecommunication, navigation and human space exploration, the ESA points out.  NASA's website notes that the International Space Station has shields to protect it and can change orbit, if necessary, to avoid space junk.

Has there ever been a collision in orbit? Yes. A privately owned U.S. communications satellite and a defunct Russian military satellite were destroyed in an accidental collision in 2009.

How are scientists addressing the problem? At the press conference, scientists discussed methods to remove the space debris from orbit. (See video below to learn about the ESA's proposal.) NASA has an office on orbital debris as well. 
      “Important progress is being made on technologies to remove the large debris from orbit,” said Hugh Lewis of the United Kingdom Space Agency. At the same time, “small debris poses a real threat to safety of space flight, and we need solutions for this population as well.”



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