News, Science & Technology

Sifting Through All That Space Junk

Eight centuries into the future, the human race has abandoned a decimated Earth and left a thick layer of space junk orbiting the planet.

That is the premise of last year’s animated film ‘WALL-E’ ‘-‘- a science fiction creation ‘-‘- but’ real humans are actively dumping increasing amounts of clutter into the space just beyond our atmosphere.

Although EVE, WALL-E’s love interest, could fly her ship easily through the intergalactic junkyard in the film, orbital debris poses a serious threat to today’s real-life spacecrafts, and the growing volume is becoming a obstacle for each subsequent spaceflight.

This month alone, the $100 billion International Space Station has had three close calls with debris.

In the second week of March, the astronauts aboard the ISS had to hunker down in the Russian Soyuz ‘lifeboat’ capsule in case there was a collision that rendered the station uninhabitable. NASA was tracking a five-inch piece of a spent rocket motor that did miss the station, but could have caused catastrophic damage had it made contact. The piece came so close to the station the astronauts could watch it fly by outside their window, according to the Los Angeles Times.

Days later, NASA monitored another piece of debris that came close to the station, and allowed the astronauts to stay on board, according to ABC News.

The Space Shuttle Discovery, which docked with the ISS after the two incidents, had to maneuver the station into a new position to avoid a four-inch piece of a spent Chinese satellite last week. The piece would have crossed into the station’s orbit for several days had the shuttle not steered the ISS out of the way, according to the Associated Press.

The U.S. Space Surveillance Network, a component of the Department of Defense, catalogs all orbital debris. Currently, it tracks more than 19,000 objects that are 10 centimeters, about the width of a softball, or larger. Less than 1,000 of these objects are operational spacecraft.

Debris larger than one centimeter, about the length of a paper clip, are the most dangerous ,and there are more than 300,000 known orbiting objects of this size. The number of debris larger than one millimeter increases by an order of magnitude, Nicholas L. Johnson, chief scientist for orbital debris at NASA’s Johnson Space Center, said.

The average collision speed in low Earth orbit is 10 kilometers per second, Johnson said. At that speed, even debris as small as a couple of centimeters can cause serious damage.

In February, two satellites collided 770 kilometers (470 miles) above northern Siberia, creating a massive field of debris that will eventually spread across the entire globe. The crash between the privately owned Iridium 33 communications satellite and the defunct Russian Cosmos 2251 satellite is the first known collision between two intact satellites and the first random catastrophic collision, Donald J. Kessler, a former NASA scientist, said.

‘The debris cloud created by this collision is like a shotgun blast that threatens other satellites in the region,’ David Wright, senior scientist and co-director of the global security program at the Union of Concerned Scientists, wrote in a paper.

In 1978, Kessler, then at NASA’s Johnson Space Center, co-wrote a paper predicting that debris density was increasing at a rate that would allow eventually enable random catastrophic collisions.

The Kessler Syndrome, as this scenario is now called, explains that the larger debris involved in an initial catastrophic collision, like the whole satellites in the February incident, will break down into smaller pieces that can then catastrophically collide with other debris, increasing the amount of debris exponentially and potentially causing a domino effect of destruction.

‘If something weighs 1,000 pounds, it can be totally broken up by something that is one pound,’ Kessler, now a consultant in North Carolina, said.

The space up to 2,000 kilometers (1,240 miles) above the Earth’s surface, known as low Earth orbit, is a densely populated area where most satellites orbit and all human spaceflights since the Apollo lunar missions take place. The ISS is also within the debris-thick LEO, Wright said.

Some satellites have shields that can protect against collisions of anything one centimeter or smaller but this material adds weight and cost, Kessler said.

Debris between one and five centimeters are usually too big for shielding to protect against but too small to be tracked from the ground, Wright, at UCS, said.

In January 2007, a Chinese anti-satellite missile test destroyed a weather satellite at 865 kilometers altitude, according to MSNBC.

‘They introduced, literally, a couple thousand more catalog fragments,’ Kessler said. ‘Those are all objects roughly bigger than a softball.’

The United States performed its first successful anti-satellite test in 1985. Using the instruments available at that time, scientists cataloged 280 pieces of debris created from the test.

‘At the time, they could detect and track the biggest 280 pieces of debris,’ Wright said. ‘But somehow that got stuck in people’s minds, ‘Oh, you blow up one of these things, and it doesn’t create that much debris.’

The destruction of a 10-ton spy satellite, the sort of thing that might be targeted in a military conflict, could double or triple the total amount of debris in LEO, Wright said.

The amount of orbital debris will continue to rise as satellites and space flights become available to more governments and companies. But right now, there is no way to clean up what is already up there.

‘No practical and affordable means of removing debris from Earth orbit has yet been identified,’ Johnson said.

Strides have been made in mitigating the accumulation of debris though not in removal. Since the 1990s, spacefaring nations and their space agencies have come together as the Inter-Agency Space Debris Coordination Committee to establish guidelines to lessen the debris contribution of space exploration.

One strategy to lessen the damage done by collisions is to prevent them from exploding upon impact. If two pieces of debris collide and some fuel remains in either piece, an explosion can occur that sends many smaller pieces debris into orbit. Under the current guidelines, vessels should dump any remaining fuel before going inoperable to avoid explosions.

The guidelines also recommend that anything put into LEO should remain in an orbit in which it will return to Earth within 25 years.

‘Those two things are fairly inexpensive things to do if you plan them before you launch the object,’ Kessler said. ‘But once you’ve got the object is in space and you don’t plan it that way, it essentially takes as much money to get it down as it did to get it up there.’

But without any means of enforcement, debacles, such as the Chinese missile test, expose the inadequacies of mitigation techniques and the need for viable means for removal in the future.

There is one sure way to clean up space junk. Debris does eventually fall out of orbit and back to Earth, although it can take decades or longer.

Cataloged debris fall back to Earth at a rate of about one per day, Johnson said. Most debris burn up upon reentry, and those that do survive usually land in the ocean or sparsely populated regions like the Australian Outback or Siberia. Falling orbital debris has never injured anyone on Earth, he said.

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