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Earth walls itself in with space junk

DPA, MOSCOW
Wednesday, Jul 16, 2003, Page 16

A computerized picture simulation by the European Space Agency depicts all the space junk orbiting our planet. PHOTO: DPA

The first collisions and explosions have already happened and the alarm bells are ringing: our planet is slowly walling itself in with a dangerous mass of speeding space junk.

Russian space debris experts and their US colleagues at NASA count up to 10,000 objects over 10cm in diameter that circle the earth, a silent armada of mankind's mess -- spent rocket stages and satellites, pieces of exploded and lost space equipment.

Then there are more than 100,000 objects between 1cm to 10cm, too small to be tracked by radar like the first category but potentially just as dangerous. These include nuts, bolts and other remnants.

Moving with an average relative velocity of about 10km a second they can wreck a satellite or, in the worst case scenario, rip into a manned spacecraft or even the International Space Station (ISS).

Even a tiny particle of a few millimeters will pierce an astronaut's space suit like a sniper's bullet if he is working outside.

"You essentially play the odds in this question of space debris -- it's part of the mission you have no control over," said William Johnson, an American radar designer and participant in NASA missions.

"Debris isn't an issue in interplanetary missions but in earth missions it is, especially on manned ones. What you worry about is paint flakes -- if one of those hits you, it'll make your day!"

Russian experts point out that for the time being, the odds are on our side, although freak incidents are occurring more often.

"For the most populated orbits the average probability is that a serious incident may happen once in 15 to 20 years, so the risk can still be considered acceptable," said Sergey Kulik, debris specialist at the Rosaviakosmos aerospace agency in Moscow.

He likes the comparison with a swimmer in the ocean -- he knows there are man-eating sharks out there somewhere but he can't fret about it every time he takes a dip.

But what if those sharks were to breed at an exponential rate?

At the current pace of cosmic littering, the coming years are predicted to bring our spacefaring species down to earth with a bump.

Called collisional cascading, or the Kessler effect (named after the former chief of the US orbital debris program, Donald Kessler), the process involves chunks of debris colliding and shattering into many smaller pieces that will hit others and so on.

"If his estimates prove to be true it could become impossible to fly in space. The probability that you'd get holed would increase drastically," says Kulik.

Kessler predicted the process will begin around 2030, although some scientists in the field believe it has already.

Another critical factor today is orbital explosions, often caused by chemical reactions in dregs of fuel in old spacecraft. More than 100 rockets and satellites have reportedly blown up in space.

The most debris created by one of these was when the upper stage of a US Pegasus rocket exploded in 1996, two years after it was launched. The burst generated a cloud of some 300,000 fragments larger than 4mm, 700 of which were over 10cm and large enough to be catalogued and tracked.

Other incidents in recent years show that the debris question isn't just the imaginary bogeyman of space exploration.

In the same year as the Pegasus blast, the French Cerise satellite was knocked out by a fragment of an exploded Ariane rocket stage in the first recorded debris collision.

The Hubble Space Telescope was also later found to have a hole punched in one of its solar panels. More worryingly, something struck a window on the ISS in February last year, leaving a sizeable impact mark.

Work is underway to fit the ISS with shields that will withstand impact by up to 1cm-big objects. In the case of 1cm to 10cm chunks, the ones not tracked by radar, the odds are the only protection.

Since it went into orbit in 1998, the outpost performed six evasive maneuvers as satellites and large pieces of debris came close to its flight path 400km above the earth.

A limited cleansing effect is observed in lower orbits of up to 600km, as gravitational pull and low aerodynamic drag slowly sucks debris into the atmosphere where it incinerates.

There is no such relief in higher orbits. One concern is our steady pollution of the geostationary orbit 36,000km from the planet, invaluable to mankind because satellites deployed here hold the same point above the earth's surface.

Since much of the overall clutter in space is caused by old satellites -- there are about 750 in operation, all of which will eventually become refuse -- one goal that is agreed upon by space agencies, is to dispose of them properly.
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