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清除地球轨道碎片太空垃圾的难题

更新时间:2018-3-18 10:12:55 来源:纽约时报中文网 作者:佚名

The quest to tackle the rubbish dump in orbit
清除地球轨道碎片太空垃圾的难题

It was a breathtaking sight. Two Falcon Heavy boosters performed a synchronised vertical landing and, minutes later, another indelible image entered the world’s imagination. A bright red sports car orbited the Earth. The man responsible, SpaceX’s Elon Musk, received widespread acclaim for launching the largest rocket since Apollo’s Saturn V. The car divided opinion.

两枚"重型猎鹰"(Falcon Heavy)助推器同步完成了垂直登陆,场面令人震惊窒息。几分钟之后,呈现在世人面前的是另一幅令人难忘的景象——一辆鲜红色的"跑车"在沿着地球轨道运行。来自太空探索技术公司(SpaceX)的埃隆·马斯克(Elon Musk)因为成功完成发射这枚阿波罗"土星5号"(Apollo's Saturn V)运载火箭之后尺寸最大的火箭而受到广泛赞誉。但是,这辆"跑车"却引发了争议。

It was either a cheerleader for space science, a marketing masterpiece or, as the mannequin astronaut enjoyed planetary selfies, another potentially dangerous temporary piece of space junk.

它可能是太空科学的推动者,或者是一次成功的公关营销活动,但也可能是另一个临时性的、可能具有危险性的太空碎片?

There are over half a million pieces of debris that are not much larger than a marble, littering the Earth’s orbit and over 20,000 the size of a cricket ball or larger. These bigger pieces range from an astronaut’s glove to dead spacecraft and disused rocket stages. Yet size does not always equate to the greatest danger.

从宇航员的手套到废弃的航天器和单级火箭,地球轨道上凌乱地散布着超过50万枚弹球大小的碎片和2万多枚板球大小的碎片。但是,碎片的危险程度并不与碎片尺寸成正比。

As we enter a new space race, with more nations like China and India joining the quest to explore the cosmos, we will be adding more and more of this flotsam into orbit. The next generation of space scientists face a big challenge: how to ensure our future wave of spacecraft survive this ever-increasing belt of rubbish.

随着新一轮太空竞赛的开展,中国、印度等更多国家加入了探索宇宙的行列,人类将在地球轨道内制造越来越多的漂浮残骸。下一代太空科学家将面临一个重大挑战:如何确保未来的航天器在这不断扩张的"垃圾地带"中生存?

The search is on for ways to keep the world’s space agencies one step ahead of this potentially lethal debris.

相关人员目前正在寻找方法让全球的太空机构能前瞻性地处理这些可能具有致命性的碎片。

“Millimetre-sized orbital debris pose the highest penetration risk because of the high impact speed to most operational spacecraft in low-Earth orbit,” says Nasa’s chief scientist for orbital debris, Jer Chyi Liou.

美国国家航空航天局(NASA)轨道碎片首席科学家Jer Chyi Liou说道:"毫米级别的轨道碎片造成的穿透风险最大,因为它对在近地轨道上的大都数航天器会产生很高的冲击速度。"

These tiny fragments far outpace the punch of a moving bullet, with maximum speeds approaching 30,000mph (48,000km/h).

这些微小碎片的速度超过子弹的飞行速度,最高接近3万英里/小时(4.8万公里/小时)。

In early February 2018 in Vienna, during the United Nations’ 55th Session of the Scientific and Technical Subcommittee Committee on the Peaceful Uses of Outer Space, Liou presented an update on the space debris environment and the US space agency’s operations and research. In 2017 alone, 86 launches around the world placed more than 400 spacecraft into orbit around the Earth.

2018年2月初,联合国宇宙空间和平利用委员会(Committee on the Peaceful Uses of Outer Space)科学和技术分委会(Scientific and Technical Subcommittee)第55次会议在维也纳召开。此次会议上,Jer Chyi Liou陈述了关于太空碎片环境及NASA运营和研究情况的最新进展。仅2017年,全球就开展了86次发射活动,在地球轨道上放置了超过400架航天器。

“The total amount of material in Earth orbit is more than 7,600 tonnes,” Liou says. “About 23,000 large objects are being tracked by the US Strategic Command’s Space Surveillance Network (SSN). In addition, there are tens of millions or more debris too small to be tracked by the SSN but still large enough to threaten human spaceflight and robotic missions.”

"地球轨道上的物质总量超过7600吨,"Jer Chyi Liou说:"美国战略指挥部(US Strategic Command)的空间监视网(Space Surveillance Network, SSN)正在跟踪约2.3万个大型物体。此外,有数以千万计或更多的碎片由于尺寸太小,SSN无法跟踪,但这些碎片的尺寸仍足以威胁人类航天活动和机器人飞行任务的实施。"

There is also the risk, known as the Kessler Syndrome or Kessler Effect, where one piece of debris breaks off and hits another so that it becomes a cascade, which could end up polluting an entire orbit for satellites. Space is already part of everyday life, from telecommunications to disaster monitoring, the loss of any satellite is a significant issue.

此外,太空还存在被称为"凯斯勒症候群"(Kessler Syndrome)或"凯斯勒效应"(Kessler Effect)的风险,即一个碎片碎裂并撞击另一个碎片,引发一连串撞击,最终污染卫星的整个轨道。从远程通信到灾难监控,太空已成为人类日常生活的一部分,任何卫星的丢失都是一个严重的问题。

The amount of debris escalated sharply in 2007 when China deliberately destroyed its Fengyun-1C weather satellite as part of an anti-satellite device test. Two years later an American Iridium 33 communications satellite collided with a spent Russian Cosmos 2251 spacecraft. Both these incidents will have ramifications for some time.

2007年,太空碎片数量激增,因为中国在一次反卫星装置试验中有意击毁了"风云-1C"气象卫星。两年之后,美国"铱33"通信卫星与俄罗斯报废的"宇宙2251"卫星发生了碰撞。这两次事件都在很长一段时间内产生持续性的后果。

Last year, Nasa was involved in 21 collision avoidance manoeuvres by uncrewed spacecraft. Four were to avoid debris from Fengyun-1C; two to avoid parts from the Iridium 33-Cosmos 2251 collision.

去年,美国国家航空航天局利用无人驾驶航天器实施了21次防碰撞演习,其中四次演习的目的是躲避"风云-1C"卫星产生的碎片,两次演习的目的是躲避"铱33"和"宇宙2251"碰撞所产生的零部件。

Moving an object out of the way by altering its orbit is one method of diverting a potential crash, but the sheer amount of debris requires constant observation and prediction – by any means necessary.

避免潜在碰撞的一个方法是改变物体轨道令物体"让路"。但是,由于碎片数量巨大,需采取所有必要的手段开展持续的观察和预测活动。

“Nasa uses a combination of radars, telescopes, and in-situ measurements to monitor, but not track, objects down to sub-millimetre in size,” says Liou.

"美国国家航空航天局将雷达、望远镜与现场测量相结合,对尺寸小至亚毫米级别的物体进行监控(但不是跟踪),"Jer Chyi Liou说道。

Nasa’s Space Debris Sensor orbits the Earth on the International Space Station. The sensor, a one-metre-square bit of kit around 20cm thick, was attached to the outside of the space station’s European Columbus module in December 2017. It will detect millimetre-sized pieces of debris for at least two years, providing information on whatever hits it – such as size, density, velocity, orbit – and will determine whether the impacting object is from space or a man-made piece of space debris.

国际空间站上的美国国家航空航天局太空碎片感应器(Space Debris Sensor)围绕地球轨道运行。该感应器尺寸为1立方米,厚度约20厘米,外形有点像工具箱,于2017年12月连接至国际空间站欧洲"哥伦布"实验舱的外部。它将在至少两年的时间内开展毫米级碎片探测活动,提供关于对它产生撞击的所有物质的信息——尺寸、密度、速度、轨道等,并确定撞击物是来自太空还是属于人为产生的太空碎片。

The United States is responsible for only around one-in-three of all known pieces of debris in low-Earth orbit so Nasa isn’t the only organisation working on the problem. This is an international effort that affects every space-faring nation; Russia’s space agency has already signed an agreement to install a new debris-tracking telescope in Brazil.

近地轨道内所有已知的碎片中,仅有约1/3是美国制造的。因此,美国国家航空航天局并非唯一研究太空碎片问题的机构。国际上的研究活动影响每一个在外太空开展活动的国家。俄罗斯的太空机构已签署一份在巴西安装新的碎片追踪望远镜的协议。

There is also a market for private initiatives to monitor space debris and sell data to satellite operators. This includes ExoAnalytic Solutions in the US and Space Insight in the UK – the latter operates a ground-based system of sensors in Cyprus. In Spain, the Deimos Sky Survey uses a network of telescopes to track near Earth objects such as asteroids as well as space debris. It also spotted Elon Musk’s car in space.

旨在监控太空碎片并向卫星运营机构出售数据的私人计划同样拥有一定的市场。此类计划包括美国的"ExoAnalytic Solutions"和英国的"Space Insight",后者在塞浦路斯运行一套地面感应器系统。在西班牙,"Deimos Sky Survey"利用一个望远镜网络追踪小行星、太空碎片等近地物体,并曾识别出埃隆·马斯克的"跑车"。

But not every piece of debris can be dealt with by collision avoidance. In April, the first European Active Debris Removal mission will launch from a SpaceX Falcon 9 rocket on its way to resupply the International Space Station. Called REMOVEdebris, the satellite will contain two cubesats that will release simulated space debris so that it can then demonstrate several ways of retrieving them.

但是防碰撞措施并不能处理所有碎片。四月,首个"欧洲主动清除碎片"(European Active Debris Removal)任务将由太空探索技术公司的"猎鹰9号"运载火箭发射升空。该任务旨在为国际空间站提供补给。名为"REMOVEdebris"的卫星包含两个立方体卫星,通过释放仿真的太空碎片验证收回碎片的若干种方法。

Four key technologies will be tested, says Guglielmo Aglietti, director of the UK’s Surrey Space Centre, which is coordinating the mission. These include a visual navigation system, a net and a harpoon used to capture debris and a de-orbit sail use to slow the debris so it falls into the Earth’s atmosphere.

此次任务的协调机构英国萨里太空中心(Surrey Space Centre)主任古列尔莫·阿格列提(Guglielmo Aglietti)表示,此次任务将测试四项关键技术。这四项技术包括视觉导航系统、用于捕捉碎片的网子和叉子及用于减慢碎片速度、令其坠入地球大气中的脱离轨道装置。

A harpoon in space sounds far-fetched but, for larger pieces of debris, it could be all that is needed. For this demonstration, the harpoon, built by Airbus Defence & Space in the UK, is the size of a pen.

在太空中设置一套叉子听起来匪夷所思,但它可以满足捕捉较大尺寸碎片的所有需求。验证工作所采用的叉子由空中客车防务与空间公司在英国制造,尺寸与钢笔相仿。

The mission will deploy a 10-sq-cm panel on a boom 1.5m (5ft) away. The tethered harpoon will then be fired from the spacecraft to pierce and retrieve the panel. The net idea is similarly simple; it will surround and trap debris.

离叉子1.5m处的吊杆上将布置一个10平方厘米大小的试验板。之后,用绳系住的叉子将从航天器中射出,刺穿并收回试验板。网子用于包围并控制碎片,其原理也很简单。

The experimental drag sail, which is a plastic membrane, can only be tested after the other technologies. “During a real mission this would be the last phase,” says Aglietti, “when the platform and the debris that it has captured are deorbited together.”

实验用的脱离轨道装置是一个塑料膜。它的测试必须在其他几项测试完成后进行。"这是此次任务的最后一个阶段,"阿格列提说:"在平台和它所捕捉的碎片一起脱离轨道之后启动。"

If REMOVEdebris is a success, this will be the start of further missions. “We will have demonstrated that space debris removal could be done using relatively low-cost technologies,” says Aglietti, “and therefore we hope that commercial ventures could follow and perform removal of the debris that poses the highest threat.”

如果REMOVEdebris获得成功,欧洲后续将启动更多的任务。"我们已经证实,利用相对低成本的技术可以清除太空碎片,"阿格列提说:"因此,我们希望商业机构后续可以跟进,致力于清除威胁性最大的碎片。"

Testing technologies on controlled simulated pieces of debris is an important step forward. The next stage – using technologies on uncontrolled pieces of debris – will be more complex and Esa is proposing a mission called e.deorbit to its member states at the end of 2019.

在受控制的仿真碎片上对各项技术进行测试是任务推进的一个重要步骤。下一阶段的工作是在不受控制的碎片上实施各项技术。这项工作更为复杂。欧洲航天局正在向其成员国建议在2019年底启动一项名为"e.deorbit"的任务。

“E.deorbit will demonstrate that we can remove an uncontrolled object safely from orbit,” says Holger Krag, head of Esa’s space debris office. “It could be an Esa satellite that’s defunct and will no longer react to any command from the ground. We would, for the first time, apply technology to a target satellite that’s real.”

"e.deorbit将证实,我们可以将不受控制的物体安全地从轨道中清除,"欧洲航天局负责人霍尔格·克拉格(Holger Krag)说:"我们选择的物体可能是欧洲航天局报废的、不再响应任何地面指令的卫星。这是我们首次将该项技术应用于真实的目标卫星。"

The removal spacecraft will be equipped with a sensor suite in order to approach the satellite safely. This is no mean feat. “It is a challenge to approach a controlled object like the ISS for docking,” says Krag, who is based at the European Space Operations Centre in Darmstadt, Germany.

开展碎片清除工作的航天器将安装感应器组件,目的是安全地接近卫星。这不是一件容易的事情。克拉格表示:"接近国际空间站等受控制的物体与其对接是一项挑战,"德国达姆施塔特市(Darmstadt)的欧洲太空控制中心(European Space Operations Centre)是克拉格工作的地方。

The uncontrolled satellite could also be tumbling or spinning. “If it’s tumbling you have to synchronise yourself and then somehow capture it. You could use a robotic arm, net or harpoon and the next step then is to apply a manoeuvre in order to bring it down.”

不受控制的卫星可能以歪斜或旋转的姿态运行。"如果它是歪斜的,你必须和它保持同步,以便通过某种方法捕捉它。你可以使用机械臂、网子或叉子。捕捉之后的步骤是是采用某种策略让它降落。"

Esa has already had a close call. In August 2016 a centimetre-sized particle hit one of the solar arrays on Esa’s Sentinel 1A satellite and produced a small reduction in power and a slight change in the spacecraft’s orbit and orientation.

欧洲航天局也曾遭遇意外。2016年8月,一个厘米级的颗粒撞击欧洲航天局"哨兵1A"卫星上的太阳能电池板,导致动力略有下降,并使该卫星的轨道和方向出现了轻微的变化。

“We take space debris seriously because we are operating a fleet of 20 satellites from here in Darmstadt,” says Krag. “Ten of them are flying in a very densely polluted area of space and we regularly have to conduct collision avoidance manoeuvres.”

"我们很重视太空碎片问题,因为我们正在达姆施塔特运行着由20个卫星组成的卫星编队,"克拉格说道:"其中有10个正在污染非常严重的太空区域飞行。我们必须定期实施防碰撞策略。"

But Krag is also pragmatic about the scale of the problem. “We can limit the risk but cannot completely avoid the risk between collisions,” he says. “We can just do our best.”

关于太空碎片问题的规模,克拉格的看法颇为务实。他说:"我们可以限制但不能完全避免碰撞风险。我们只能尽力而为。"

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