[ti:What Is Space Junk and How Dangerous Is it?] [by:www.51voa.com] [00:00.00]更多听力请访问51VOA.COM [00:00.04]American and European officials [00:03.48]sharply criticized Russia's recent missile test [00:08.08]that exploded an orbiting satellite into many pieces. [00:14.80]Scientists said this orbiting debris [00:18.76]will increase risks to humans [00:21.96]and their efforts in space for years to come. [00:26.76]But, what is this debris – also called space junk [00:32.60]-- and what are the safety threats it presents? [00:37.52]Space debris is anything humans [00:40.96]have placed in space but no longer use. [00:44.84]The junk floats around hundreds of kilometers above Earth. [00:50.84]Experts say the main worry is that such debris [00:56.00]will hit a space station, satellite or other equipment. [01:01.84]Space debris orbits around the Earth very fast [01:06.64]- about 25,000 kilometers per hour in low-Earth orbit. [01:13.36]The junk could cause major damage [01:17.00]if it hits satellites or spacecraft. [01:20.96]"Every satellite that goes into orbit [01:24.80]has the potential of becoming space debris," [01:28.88]said Professor Hugh Lewis, [01:31.56]with Britain's University of Southampton. [01:35.52]Lewis, who heads the university's Astronautics Research Group, [01:41.32]spoke to Reuters news agency. [01:44.56]With the number of satellite deployments rising, [01:49.16]near-Earth space will likely see more space debris in the coming years. [01:56.48]Russia is not the only country to have destroyed a satellite. [02:01.92]China, the United States and India [02:05.72]have also carried out anti-satellite missile tests. [02:10.92]The U.S. government tracks about 23,000 pieces of debris [02:17.20]larger than a softball orbiting the Earth. [02:21.84]About 500,000 pieces of debris are larger than one centimeter [02:28.80]and 100 million pieces are about one millimeter or larger. [02:35.32]Holger Krag is head of the European Space Agency's [02:40.76]Space Safety Program Office. [02:44.20]He told Reuters that if the build-up of debris continues, [02:49.56]some areas of space might become unusable. [02:54.28]The satellite Russia just destroyed had been launched in 1982. [03:01.68]It weighed more than 2,000 kilograms. [03:06.16]American officials said the test [03:09.68]created more than 1,500 pieces of "trackable orbital debris." [03:17.20]The U.S. Space Command said the missile strike [03:21.60]likely created hundreds of thousands [03:24.96]of additional smaller pieces of debris. [03:29.08]Crew members aboard the International Space Station (ISS) [03:33.68]were directed to take shelter in their attached spaceship capsules [03:39.00]for two hours after the test. [03:41.92]The safety measure was taken in case the crew had to leave [03:47.68]because of possible damage from debris. [03:50.80]The American space agency NASA [03:54.72]says debris in orbits 600 kilometers or less from Earth [04:01.04]will fall back to the planet within several years. [04:06.16]But space junk above 1,000 kilometers [04:10.56]is expected to continue circling for a century or more. [04:16.68]"If we want to try and solve the space debris problem, [04:21.56]we have to start to remove that type of object," [04:25.76]said professor Lewis of the University of Southampton. [04:30.96]Japan's Aerospace Exploration Agency (JAXA) [04:35.24]and the European Space Agency (ESA) [04:38.32]have partnered with private companies [04:41.32]to find ways to remove space debris. [04:45.40]In addition to being a threat to space property and astronauts, [04:51.32]debris also increases the cost for satellite operators. [04:56.92]Industry experts have estimated [05:00.40]that protection and reduction efforts dealing with space junk [05:05.72]make up about 5-10 percent of satellite mission costs. [05:12.52]One study by the Organization for Economic Co-operation [05:17.60]and Development (OECD) found that the costs [05:21.04]for lower-Earth orbits were even higher. [05:24.84]I'm Bryan Lynn. 更多听力请访问51VOA.COM