A段落

Last year, commercial companies, military and civil departments and amateurs sent more than 400 satellites into orbit, over four times the yearly average in the previous decade. Numbers could rise even more sharply if leading space companies follow through on plans to deploy hundreds to thousands of large constellations of satellites to space in the next few years.

All that traffic can lead to disaster. Ten years ago, a US commercial Iridium satellite smashed into an inactive Russian communications satellite called Cosmos-2251, creating thousands of new pieces of space shrapnel that now threaten other satellites in low Earth orbit – the zone stretching up to 2,000 kilometres in altitude. Altogether, there are roughly 20,000 human-made objects in orbit, from working satellites to small rocket pieces. And satellite operators can’t steer away from every potential crash, because each move consumes time and fuel that could otherwise be used for the spacecraft’s main job.

B段落

Concern about space junk goes back to the beginning of the satellite era, but the number of objects in orbit is rising so rapidly that researchers are investigating new ways of attacking the problem. Several teams are trying to improve methods of assessing what is in orbit, so that satellite operators can work more efficiently in ever-more-crowded space. Some researchers are now starting to compile a massive data set that includes the best possible information on where everything is in orbit. Others are developing taxonomies of space debris – working on measuring properties such as the shape and size of an object, so that satellite operators know how much to worry about what’s coming their way.

The alternative, many say, is unthinkable. Just a few uncontrolled space crashes could generate enough debris to set off a runaway cascade of fragments, rendering near-Earth space unusable.’If we go on like this, we will reach a point of no return,’ says Carolin Frueh, an astrodynamical researcher at Purdue University in WestLafayette, Indiana.

C段落

Even as our ability to monitor space objects increases, so too does the total number of items in orbit. That means companies, governments and other players in space are collaborating in new ways to avoid a shared threat. International groups such as the Inter-Agency Space Debris Coordination Committee have developed guidelines on space sustainability. Those include inactivating satellites at the end of their useful life by venting pressurized materials or leftover fuel that might lead to explosions. The intergovernmental groups also advise lowering satellites deep enough into the atmosphere that they will burn up or disintegrate within 25 years. But so far, only about half of all missions have abided by this 25-year goal, says Holger Krag, head of the European Space Agency’s space-debris office in Darmstadt, Germany. Operators of the planned large constellations of satellites say they will be responsible stewards in their enterprises in space, but Krag worries that problems could increase, despite their best intentions.’What happens to those that fail or go bankrupt?’ he asks.’They are probably not going to spend money to remove their satellites from space.’

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In theory, given the vastness of space, satellite operators should have plenty of room for all these missions to fly safely without ever nearing another object. So some scientists are tackling the problem of space junk by trying to find out where all the debris is to a high degree of precision. That would alleviate the need for many of the unnecessary maneuvers that are carried out to avoid potential collisions.’If you knew precisely where everything was, you would almost never have a problem,’ says Marlon Sorge, a space-debris specialist at the Aerospace Corporation in El Segundo, California.

E段落

The field is called space traffic management, because it’s similar to managing traffic on the roads or in the air. Think about a busy day at an airport, says Moriba Jah, an astrodynamicist at the University of Texas at Austin: planes line up in the sky,  landing and taking off close to one another in a carefully choreographed routine. Air-traffic controllers know the location of the planes down to one metre in accuracy. The same can’t be said for space debris. Not all objects in orbit are known, and even those included in databases are not tracked consistently.

F段落

An additional problem is that there is no authoritative catalogue that accurately lists the orbits of all known space debris. Jah illustrates this with a web-based database that he has developed. It draws on several sources, such as catalogues maintained by the US and Russian governments, to visualise where objects are in space. When he types in an identifier for a particular space object, the database draws a purple line to designate its orbit. Only this doesn’t quite work for a number of objects, such as a Russian rocket body designated in the database as object number 32280. When Jah enters that number, the database draws two purple lines: the US and Russian sources contain two completely different orbits for the same object. Jah says that it is almost impossible to tell which is correct, unless a third source of information made it possible to cross-correlate.

Jah describes himself as a space environmentalist:’I want to make space a place that is safe to operate, that is free and useful for generations to come.’Until that happens, he argues, the space community will continue devolving into a tragedy in which all spaceflight operators are polluting a common resource.

    A段落

去年，商业公司、军事和民用部门以及业余爱好者共向轨道发送了超过400颗卫星，比前一个十年的年均数量增加了四倍以上。如果领先的航天公司按计划在未来几年内部署数百至数千颗大型卫星星座，这一数字可能会进一步迅速增长。

所有这些交通量可能导致灾难。十年前，美国商业Iridium卫星与一颗名为Cosmos-2251的俄罗斯废弃通信卫星相撞，产生了成千上万个太空弹片，现在对低地球轨道的其他卫星构成威胁——这个区域的高度延伸到2000公里。总体而言，轨道上大约有2万个人造物体，从工作卫星到小型火箭碎片不一而足。而卫星运营商无法避开每一次潜在的碰撞，因为每一次移动都会消耗时间和燃料，否则可以用于航天器的主要任务。

B段落

对太空碎片的担忧可以追溯到卫星时代的开始，但轨道上的物体数量上升得如此之快，以至于研究人员正在探索新的方法来解决这个问题。几个团队正在努力改进对轨道物体的评估方法，以便卫星运营商可以在越来越拥挤的太空中更高效地工作。一些研究人员现在开始编制一个包含太空中所有物体最佳信息的大型数据集。其他人则正在开发太空碎片的分类法，研究测量物体的形状和大小等属性，以便卫星运营商知道需要关注什么。

很多人认为，否则将不可想象的情况。只需发生几次失控碰撞，就足以产生足够的碎片引发连锁反应，使近地空间无法使用。印第安纳州西拉非叶特市普渡大学的天体动力学研究员Carolin Frueh表示：“如果我们继续下去，我们将达到无法回头的地步。”

C段落

随着我们监测太空物体的能力增强，轨道上物体的总数也在增加。这意味着太空中的企业、政府和其他参与者正在以新的方式合作，以避免共同的威胁。国际组织如国际航天碎片协调委员会已经制定了太空可持续性指南。其中包括通过释放压力材料或剩余燃料来失活寿命结束的卫星，以免引发爆炸。这些政府间组织还建议将卫星降低到足够深的大气层中，在25年内烧毁或分解。但是，德国达姆施塔特的欧洲航天局太空碎片办公室主任Holger Krag表示，到目前为止，只有大约一半的任务遵守了这个25年的目标。计划中的大型卫星星座的运营商表示，他们将对其企业在太空中负责任地管理，但Krag担心问题可能会增加，尽管他们有最好的意图。他问道：“那些失败或破产的公司会怎么处理？他们可能不会花钱将他们的卫星从太空中清除。”

D段落

从理论上讲，鉴于太空的广阔，卫星运营商应该有足够的空间让所有这些任务安全飞行，而不会接近其他物体。因此，一些科学家通过试图准确找出所有太空碎片的位置来解决太空碎片问题。这将减少为避免潜在碰撞而执行的许多不必要的机动。“如果你准确知道每件事在哪里，你几乎永远不会有问题，”加州埃尔塞贡多市航天公司的太空碎片专家Marlon Sorge说道。

E段落

这个领域被称为太空交通管理，因为它类似于管理道路或空中交通。奥斯汀德克萨斯大学的行星动力学家Moriba Jah说，想象一下机场繁忙的一个工作日：飞机在天空中排队，靠近彼此着陆和起飞，按照精心编排的程序进行。空中交通管制员可以精确到一米的位置了解飞机的位置。对于太空碎片来说，情况并非如此。并非所有的轨道物体都是已知的，甚至那些包含在数据库中的轨道也没有得到一致的跟踪。

F段落

另一个问题是没有权威的目录准确列出所有已知太空碎片的轨道。Jah通过他开发的一个基于网络的数据库来说明这一点。它利用美国和俄罗斯政府维护的目录等多个来源，将空间中物体的位置可视化。当他输入一个特定空间物体的标识符时，数据库会绘制一条紫色线来指示其轨道。但这对于某些物体并不起作用，比如数据库中标识为对象编号32280的俄罗斯火箭本体。当Jah输入该编号时，数据库会绘制两条紫色线：美国和俄罗斯的数据源对于同一个物体包含了完全不同的轨道信息。Jah表示，除非有第三方信息源进行交叉核对，否则几乎不可能确定哪个是正确的。

Jah将自己描述为太空环境保护主义者：“我希望使太空成为一个安全、自由且有用的地方，供后代使用。”在这种情况下，他认为，太空社区将继续陷入悲剧，所有太空飞行运营商都在污染共同的资源。