Beijing, Feb 12 (Xinhua) The collision of a privately owned US communication satellite with a non-operational Russian satellite in space has highlighted the increasing threat posed by space debris.
Space debris, also called space junk or space waste, are the man-made objects in orbit around Earth that no longer serve any useful purpose.

These consist of things ranging from entire spent rocket stages and defunct satellites to explosion fragments, paint flakes, dust, and slag from solid rocket motors, coolant released by nuclear powered satellites, and other small particles.

Space junk has been a growing concern for the countries pursuing space exploration, as collisions at high orbital velocities can be highly damaging to functioning satellites and can also produce even more space debris.

Since the former Soviet Union sent the first satellite into space in 1957, human exploration of space has left a large number of debris in space.

At the beginning of this year, there were roughly 17,000 pieces of man-made debris orbiting Earth, said Nicholas Johnson, chief scientist of NASA’s Orbital Debris Program Office at the Johnson Space Center in Houston.

Last April, scientists at the American Physical Society conference in Los Angeles said there were more than 150 million pieces.

Statistics showed that about 45 percent of space debris was produced by the US.

The average speed of space debris is 10 km per second and the maximum speed can be 16 km per second. An explosion could happen if the craft is hit by a large piece of space debris.

Even a 10-gram piece of debris can generate a collision force equalling the crash of a car running at 100 km per hour, said Du Heng, chief scientist with China’s space debris action programme.

Therefore, scientists attending last April’s conference have called on the international community for joint efforts to reduce spaces debris.

The threat is that debris would begin slamming into other debris, creating a cascading effect called “super-criticality”, they said.

According to the scientists, a satellite orbiting Earth passes within 60 miles (about 96.6 km) of a piece of space junk several thousand times a day and has a one percent chance each year of getting hit.

“We are in danger of a runaway escalation of space debris,” Massachusetts Institute of Technology physicist Geoffrey Forden said.

But so far no effective way to collect space rubbish or avoid collision with them has been worked out. Satellite and spacecraft launchers can only try producing as little debris as possible while monitoring large debris and improving solidity of space vessels.

According to Du, less debris is nowadays produced by the explosion of abandoned rockets with surplus fuel.

Improvements in spacecraft have also been made, including designing special protection areas. The measures on the International Space Station seem effective in resisting the collision with small debris. Space powers are also trying to enhance monitoring abilities and aim at lowering the size of debris to one centimetre.