VOA标准英语2014--Scientists Deliberate Cleaning Space Junk（在线收听）

Scientists Deliberate Cleaning Space Junk

WASHINGTON — Everything that we launch into an orbit around the earth eventually becomes space debris. Scientists say the increasing number of unusable objects circling our planet is threatening functioning satellites as well as humans flying into space. The European Space Agency, or ESA, plans to solve the problem.

The U.S. space agency NASA says there are half a million pieces of space debris, with more than 20,000 larger than an apple. Most are speeding along at about seven kilometers per second, or more than 25,000 kilometers per hour.

At that speed, the impact of even a cherry-sized piece of metal is enormous, said the deputy head of ESA Space Debris Office, Holger Krag.

“At this velocity both objects will shatter into pieces, this will be bad for the object concerned but it will also be bad for the rest of the environment, because we will add additional fragments which again then are candidates for future collisions,” said Krag.

Scientists monitor the path of space debris and sometimes reposition satellites or even the International Space Station to avoid collisions. But, Krag said, keeping track of the orbiting junk requires powerful sensors.

“The U.S. Space Strategic Command is in possession of those sensors, it's a relic of the Cold War, to detect approaching missiles. And it is a global network of radar and telescope stations on the ground observing space continuously all of the time,” said Krag.

Loss of communications, GPS or a scientific satellite could have potentially devastating effects, so scientists are exploring options for removing dangerous debris.

“That means planning a mission that goes there, approaches, rendezvous and captures the object, berths it, and then does the controlled orbit maneuver.  This is a very complex technology that will be required for that,” explained Krag.

Several designs are in consideration, such as a satellite that fires beams of charged particles that gradually slow down flying objects, dragging them into the atmosphere where they will burn up.

Smaller objects could be shot down with ground-based lasers, while large ones that could break up into thousands of smaller pieces may be brought down with special robotic satellites.

Even though such missions could cost up to $200 million, Krag says they should start as soon as possible to prevent the chance of larger collisions that could send many thousands of additional pieces on a deadly flight around the earth.