According to a study released by the National Research Council, more than 4,500 spacecraft have been launched into space since 1957 and, although nearly 2,200 of them remain in orbit, only 450 still are functional. In addition to the 1,750 non-functioning spacecraft that continue orbiting, Earth is surrounded by a thin belt of all kinds of space-crap: upper-stage launch vehicles, solid rocket motor slag, paint-chips, lens-caps, bolts and what NASA calls "other mission-related debris."
Last March, Russia brought the Mir space station back down to Earth over the South Pacific. Over 1,500 Mir fragments, some as large as cars, were expected to reach Earth, falling mainly on the 16 island states that form the South Pacific Forum.
No one was hurt but, according to news reports, the Russian space agency took out a $200 million insurance policy with insurance giant Lloyd's of London before retrieving Mir, to protect themselves against the unforeseeable. Left in space, Mir would have become just another piece of orbital debris, albeit the largest one up there.
Dr. Jeffrey Theall, an orbital-debris scientist at NASA's Johnson Space Center in Houston, Texas, says there are plenty of man-made objects orbiting Earth already.
"Ten thousand are in the U.S. Space Command catalog," he says. "That includes all the objects that Space Command can see." Theall says there are probably tens of millions of orbiting particles that are too small to detect.
Just 60 years ago there was nothing but pristine, inky space -- and now it's messier than a freshman's dorm room
I blame the Russians.
Orbital debris can be a big problem, interrupting space missions, threatening satellites and endangering astronauts. Just think about it: 2,000 kilometers above Earth, in zero-gravity conditions, a chip of aluminum paint can travel at speeds of eight kilometers per second. Theall says collision with a paint-chip measuring one-tenth of a millimeter across could have devastating consequences for an astronaut.
"That will penetrate a spacesuit," he says matter-of-factly.
In photographs taken before its retrieval, Mir bore the marks of multiple collisions with orbital debris. The space shuttles are routinely maneuvered to avoid collisions. On March 14, NASA moved the International Space Station to avoid part of a foot-restraint system traveling toward the station at 17,000 miles per hour after being dropped by clumsy U.S. astronaut Jim Voss during a routine space walk.
But I'm going to blame the Russians for that one, too.
In New Mexico's remote Lincoln National Forest stands the NASA Orbital Debris Observatory (NODO), providing information of the distribution of orbiting objects 24 hours a day. With radar, and telescopes like the NODO, NASA tracks and catalogs all detectable debris, assigning each piece its own number.
"For a low Earth orbiting object, they can see objects as small as 10 centimeters," Theall says.
While the U.S. Space Surveillance Network can only detect objects measuring more than 10 centimeters across, sensitive ground-based radars can detect debris as small as three millimeters in diameter. Scientists such as Theall can assess the population of even smaller pieces of orbital debris by examining impact features on the surfaces of returned spacecraft.
NASA has been tracking and cataloging orbital debris since July 1961, when an upper-stage rocket launch exploded, creating 294 pieces of orbiting debris.
"Over 30 years later, over 200 pieces were still in orbit," Theall says. "Something happens today and its still a problem 30 years down the road."
But just like Mir, smaller pieces of debris return to Earth all the time, Theall says.
"The reason Mir was so interesting was because it was so large," he says. "Nature will bring down quite a bit on its own. Roughly one per week re-enters and, in a significant number of cases, nothing survives to the ground. The Earth is three-fifths water so, most of the time, it falls in the ocean."
If debris survives re-entry and hits land instead of water, it usually falls on sparsely populated regions like the Canadian tundra, the Australian outback, or Siberia in the Russian Federation, he says. At altitudes of 600 kilometers or less, low Earth-orbiting debris returns to Earth within a few years, but at higher altitudes it takes much longer. Space debris at altitudes exceeding 1,000 kilometers will continue to orbit for over a century, gradually being drawn closer to Earth by its gravitational pull.
Since 1988, National Space Policy has required all space missions to reduce or minimize accumulation of space debris; internationally, the Inter-Agency Space Debris Coordination Committee encourages the same measures of its members, which include space agencies from Europe, Russia, Japan, China and the United States.
"If you quit creating new debris, that's the most critical thing you can do," Theall says. "It's not that space is unusable now. But if we're not careful, it could become unusable in the future."
And if that happens, who's fault will it be?
That's right, folks.
Give me an 'R.'
Give me a 'U.'
Give me a ...