太空垃圾数量已达“临界点”
<p><span word="The">The</span> <span word="amount">amount</span> <span word="of">of</span> <span word="debris">debris</span> <span word="orbiting">orbiting</span> <span word="the">the</span> <span word="Earth">Earth</span> <span word="has">has</span> <span word="reached">reached</span> "<span word="a">a</span> <span word="tipping">tipping</span> <span word="point">point</span>" <span word="for">for</span> <span word="collisions">collisions</span>, <span word="which">which</span> <span word="would">would</span> <span word="in">in</span> <span word="turn">turn</span> <span word="generate">generate</span> <span word="more">more</span> <span word="of">of</span> <span word="the">the</span> <span word="debris">debris</span> <span word="that">that</span> <span word="threatens">threatens</span> <span word="astronauts">astronauts</span> <span word="and">and</span> <span word="satellites">satellites</span>, <span word="according">according</span> <span word="to">to</span> <span word="a">a</span> <span word="US">US</span> <span word="study">study</span> <span word="released">released</span> <span word="on">on</span> <span word="Thursday">Thursday</span>.</p><p><span word="NASA">NASA</span> <span word="needs">needs</span> <span word="a">a</span> <span word="new">new</span> <span word="strategic">strategic</span> <span word="plan">plan</span> <span word="for">for</span> <span word="mitigating">mitigating</span> <span word="the">the</span> <span word="hazards">hazards</span> <span word="posed">posed</span> <span word="by">by</span> <span word="spent">spent</span> <span word="rocket">rocket</span> <span word="bodies">bodies</span>, <span word="discarded">discarded</span> <span word="satellites">satellites</span> <span word="and">and</span> <span word="thousands">thousands</span> <span word="of">of</span> <span word="other">other</span> <span word="pieces">pieces</span> <span word="of">of</span> <span word="junk">junk</span> <span word="flying">flying</span> <span word="around">around</span> <span word="the">the</span> <span word="planet">planet</span> <span word="at">at</span> <span word="speeds">speeds</span> <span word="of">of</span> 17,500 <span word="miles">miles</span> (28,164 <span word="kilomtres">kilomtres</span>) <span word="per">per</span> <span word="hour">hour</span>, <span word="the">the</span> <span word="National">National</span> <span word="Research">Research</span> <span word="Council">Council</span> <span word="said">said</span> <span word="in">in</span> <span word="the">the</span> <span word="study">study</span>.</p><p><span word="The">The</span> <span word="council">council</span> <span word="is">is</span> <span word="one">one</span> <span word="of">of</span> <span word="the">the</span> <span word="private">private</span>, <span word="nonprofit">nonprofit</span> <span word="US">US</span> <span word="national">national</span> <span word="academies">academies</span> <span word="that">that</span> <span word="provide">provide</span> <span word="expert">expert</span> <span word="advice">advice</span> <span word="on">on</span> <span word="scientific">scientific</span> <span word="problems">problems</span>.</p><p><span word="Orbital">Orbital</span> <span word="debris">debris</span> <span word="poses">poses</span> <span word="a">a</span> <span word="threat">threat</span> <span word="to">to</span> <span word="the">the</span> <span word="approximately">approximately</span> 1,000 <span word="operational">operational</span> <span word="commercial">commercial</span>, <span word="military">military</span> <span word="and">and</span> <span word="civilian">civilian</span> <span word="satellites">satellites</span> <span word="orbiting">orbiting</span> <span word="the">the</span> <span word="Earth">Earth</span> -- <span word="part">part</span> <span word="of">of</span> <span word="a">a</span> <span word="global">global</span> <span word="industry">industry</span> <span word="that">that</span> <span word="generated">generated</span> $168 <span word="billion">billion</span> <span word="in">in</span> <span word="revenues">revenues</span> <span word="last">last</span> <span word="year">year</span>, <span word="Satellite">Satellite</span> <span word="Industry">Industry</span> <span word="Association">Association</span> <span word="figures">figures</span> <span word="show">show</span>.</p><p><span word="The">The</span> <span word="world">world</span>'<span word="s">s</span> <span word="first">first</span> <span word="space">space</span> <span word="smashup">smashup</span> <span word="occurred">occurred</span> <span word="in">in</span> 2009 <span word="when">when</span> <span word="a">a</span> <span word="working">working</span> <span word="Iridium">Iridium</span> <span word="communications">communications</span> <span word="satellite">satellite</span> <span word="and">and</span> <span word="a">a</span> <span word="non">non</span>-<span word="operational">operational</span> <span word="Russian">Russian</span> <span word="satellite">satellite</span> <span word="collided">collided</span> 490 <span word="miles">miles</span> (789 <span word="km">km</span>) <span word="over">over</span> <span word="Siberia">Siberia</span>, <span word="generating">generating</span> <span word="thousands">thousands</span> <span word="of">of</span> <span word="new">new</span> <span word="pieces">pieces</span> <span word="of">of</span> <span word="orbital">orbital</span> <span word="debris">debris</span>.</p><p><span word="The">The</span> <span word="amount">amount</span> <span word="of">of</span> <span word="orbital">orbital</span> <span word="debris">debris</span> <span word="tracked">tracked</span> <span word="by">by</span> <span word="the">the</span> <span word="US">US</span> <span word="Space">Space</span> <span word="Surveillance">Surveillance</span> <span word="Network">Network</span> <span word="jumped">jumped</span> <span word="from">from</span> 9,949 <span word="cataloged">cataloged</span> <span word="objects">objects</span> <span word="in">in</span> <span word="December">December</span> 2006 <span word="to">to</span> 16,094 <span word="in">in</span> <span word="July">July</span> 2011, <span word="the">the</span> <span word="National">National</span> <span word="Research">Research</span> <span word="Council">Council</span> <span word="said">said</span>.</p><p><span word="The">The</span> <span word="surveillance">surveillance</span> <span word="network">network</span> <span word="tracks">tracks</span> <span word="objects">objects</span> <span word="approximately">approximately</span> 10 <span word="centimeters">centimeters</span> <span word="in">in</span> <span word="diameter">diameter</span> <span word="and">and</span> <span word="larger">larger</span>.</p><p><span word="Some">Some</span> <span word="computer">computer</span> <span word="models">models</span> <span word="show">show</span> <span word="the">the</span> <span word="amount">amount</span> <span word="of">of</span> <span word="orbital">orbital</span> <span word="debris">debris</span> "<span word="has">has</span> <span word="reached">reached</span> <span word="a">a</span> <span word="tipping">tipping</span> <span word="point">point</span>, <span word="with">with</span> <span word="enough">enough</span> <span word="currently">currently</span> <span word="in">in</span> <span word="orbit">orbit</span> <span word="to">to</span> <span word="continually">continually</span> <span word="collide">collide</span> <span word="and">and</span> <span word="create">create</span> <span word="even">even</span> <span word="more">more</span> <span word="debris">debris</span>, <span word="raising">raising</span> <span word="the">the</span> <span word="risk">risk</span> <span word="of">of</span> <span word="spacecraft">spacecraft</span> <span word="failures">failures</span>," <span word="the">the</span> <span word="research">research</span> <span word="council">council</span> <span word="said">said</span> <span word="in">in</span> <span word="a">a</span> <span word="statement">statement</span> <span word="released">released</span> <span word="Thursday">Thursday</span> <span word="as">as</span> <span word="part">part</span> <span word="its">its</span> 182-<span word="page">page</span> <span word="report">report</span>.</p>
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