Since the early 1960's，scientists have conducted¹ more than 3，700 space launches²，and that number keeps growing.The payloads³ range from small communications satellites to the International Space Station. Pieces are replaced or discarded. Some satellites stop working. Explosions can burst others into tiny bits. The result? There's a bunch of junk filling up space.

What's the Problem?Close to Earth，objects are slowed by gravity and friction. But hundreds of kilometers up， there's no air to slow anything down. So when a rock- et explodes， the metal fragments can move at 25，000 miles per hour. At that speed， a tiny， one-centimeter metal object packs quite a punch -- the equivalent of a 400-pound safe at 60 miles per hour.

If one of these small objects struck an unprotected astronaut or a critical part of a satellite -- or even worse， a spacecraft fuel tank -- the consequences could be catas trophic⁴.Think of a small branch flying through the air during a tornado⁵. It can cause serious damage.

Dr. William Ailor， director of the Center for Orbital⁶ and Reentry⁷ Debris⁸ Studies，says the situation in space is similar to our pollution problems here on Earth.\"We used to just put up a satellite and let it die in orbit， or not worry about lost tools，lens covers，spacecraft parts and things like that，\" Dr. Ailor says. \"But then we began to realize this debris was not only cluttering up⁹ the orbits we wanted to use，it would also do so for hundreds or thousands of years.\"

Clean It Up. Nicholas Johnson， director of NASA's Orbital Debris Research Program，says scientists have all sorts of clean-up ideas. They could use ground-and spacebased lasers or orbital electromagnets¹⁰. Somebody even came up with an idea for a giant sponge ball that could absorb debris.But the only practical approach is to not clutter things up any further.

\"We track between 7，000 and 10，000 objects by radar， and we've been able to plot¹¹ their orbits pretty accurately，''he says. \"We've put shielding on the space station， the shuttle， the satellites we put up， and we rely on the odds¹²， which are still greatly in our favor.\" It can get pretty innovative¹³，says University of New Hampshire physics professor Jim Ryan. \"The Hubble Telescope， for example，basically flies backward to protect the mirror from debris，\" he says.

自20世紀60年代初，科學家們進行的空間發(fā)射超過3700次，而且數(shù)目還在不斷增加。這些有效載重小到通信衛(wèi)星大到國際空間站，一件件被更換、遺棄。有的衛(wèi)星已停止工作。爆炸可將其他衛(wèi)星變?yōu)樾∷槠?。結(jié)果呢?——大量的垃圾將充斥太空。

問題是什么? 在近地空間，物體在重力和摩擦力的作用下減速。但在數(shù)百公里的高空卻沒有空氣使其減速。因此，火箭爆炸產(chǎn)生的金屬碎片可達到時速25000英里。在此速度下，一小塊一厘米大小的金屬塊的沖擊力相當于一個時速60英里重400磅的保險箱的沖擊力。

假設其中一小碎片撞擊到毫無防護的宇航員身上或衛(wèi)星的關(guān)鍵部位，甚至更糟糕的是撞到飛船燃料倉，都會導致災難性的后果。想想，一根被龍卷風卷到空中的小樹杈也可以導致嚴重危害吧。

軌道飛行及再入航天器殘骸研究中心主任威廉·艾勒博士認為太空中的情況和我們地球上的污染問題相似。他說：“過去我們只是發(fā)射衛(wèi)星，然后把它們遺留在軌道上，根本不擔心遺失的各種儀器設備、鏡頭護罩和宇宙飛船上的零部件之類的東西。但隨后我們意識到這些殘骸不僅現(xiàn)在擁堵在我們所需的軌道上，而且以后數(shù)百年、數(shù)千年也會如此?！?/p>

治理太空垃圾。美國太空總署軌道飛行殘骸研究項目負責人尼古拉斯·約翰遜稱科學家們設想了各種治理宇宙空間的方法：如利用地面和空間的激光束或使用軌道電磁石；有人甚至想到用一個巨大的海綿球來吸附殘骸。但是惟一切實可行的方法是不再向太空傾倒垃圾。

他說：“我們通過雷達追蹤到7000-10000個碎片，而且可以相當精確地繪出它們的運行軌道。我們?yōu)榭臻g站、火箭和發(fā)射的衛(wèi)星設置防護，我們相信成功的機率還是有利于我們?！泵绹潞辈际矤栔萘⒋髮W物理學教授吉姆·瑞安認為這極具創(chuàng)新性，他說：“例如哈勃望遠鏡基本上倒著飛行，這是為了保護鏡片不受碎片撞擊?！?/p>

注釋：

1．conductvt．進行，實施 2．launch n．發(fā)射

3．payload n．有效載重 4．catastrophic adj．災難性的

5．tornadon.龍卷風 6．orbitaladj.軌道的

7．reentryn．(航天器等的)再入，重返大氣層

8．debrisn．殘骸9．cluttervt．~up亂堆在，塞滿

10．electromagnetn．電磁體，電磁鐵11．plotvt．在圖上標繪出…的位置

12．oddsn.成功的可能性，機會 13．innovative adj，革新的，新穎的