An out-of-control Chinese space station will soon fall to Earth
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Mar 15th 2018
ITS name means “heavenly palace”. But Tiangong-1, an eight-tonne Chinese space station launched in 2011, will not remain in the heavens much longer. After visits from crews in 2012 and 2013, Tiangong-1’s mission officially ended in March 2016. A few months later China’s space agency appeared to confirm what amateur skywatchers had already suspected, that it had lost control of the station. It said it expected Tiangong-1 to fall from the sky sometime late in 2017.
它名字的意思是“天宫”。 但2011年推出的8吨重的中国空间站天宫一号,将不会在天上停留多长时间了。 机组人员在2012年和2013年访问后,天宫一号的任务于2016年3月正式结束。几个月后,中国的航天局似乎确认了它已失去对该台站的控制权,业余天空观测者对这一点早已经怀疑了。 它预计天宫一号将于2017年下半年从天空坠落。
In fact, the station is still up there, orbiting at an average height of 250km. But the inaccuracy of the agency’s prediction is understandable. At low altitudes (anything under about 2,000km), orbital mechanics is a surprisingly imprecise science. Earth’s thin outer atmosphere exerts a measurable drag on anything in such an orbit, and this drag means that, without regular boosts, that object will fall out of orbit eventually. The drag itself, however, is not constant. So exactly when this fiery fall will happen is hard to say in advance.
事实上,空间站仍在那里,轨道平均高度为250公里。 但机构预测的不准确性是可以理解的。 在低海拔(约2000公里以下的任何地方),轨道力学是令人惊讶的不精确的科学。 地球较薄的外层大气对这样一个轨道上的任何物体施加可测量的阻力,这种阻力意味着,如果没有常规的推动,这个物体最终会脱离轨道。 然而,阻力本身并不是恒定的。 所以,很难提前预测这个激烈的降落什么时候会发生。
Changes in the sun’s activity, for example, affect the density of the outer atmosphere, speeding up or slowing down the speed of an orbit’s decay. The interplay between Earth’s magnetic field and the solar wind has similar effects. In the case of Tiangong-1, though, the end is close enough for educated guesses to be made. The Aerospace Corporation, an American consultancy, reckons that April 3rd is the most likely day. The European Space Agency expects it to happen sometime between March 29th and April 9th.
例如,太阳活动的变化会影响外层大气的密度,加速或减慢轨道的衰减速度。地球磁场和太阳风之间的相互作用也有类似的影响。然而,在“天宫一号”的例子中,最终的结果已经足够接近于进行有根据的猜测了。美国的一家咨询公司,航空航天公司认为4月3日是最可能的一天。欧洲航天局预计它将在3月29日至4月9日之间发生。
As space junk goes, Tiangong-1 is big, but not especially so (the spent second stage of a Russian Zenit rocket, which is roughly the same size, re-entered the atmosphere over Peru in January). There is, nevertheless, a good chance that some parts of it will survive their descent.
随着太空垃圾的发展,天宫一号的规模很大,但并不是那么特别(俄罗斯的Zenit火箭的第二阶段,其大小(和天宫一号)差不多,今年1月重新进入了秘鲁的大气层)。然而,这是一个很好的机会,它的某些部分仍有机会在他们降落中幸存下来。
Without knowing when the station will fall, it is impossible to say where those pieces might land, though the characteristics of the station’s orbit mean it will be between latitudes 43° north (that of northern Spain) and 43° south (which passes by Tasmania; see map). Wherever they land, the pieces will come down in a long, narrow line, with the densest parts of the station travelling farthest.
如果不知道空间站何时会坠落,就不可能知道这些碎片会在哪里着陆,尽管空间站轨道的特性意味着它将在北纬43度(北西班牙)和南纬43°(经过塔斯岛,见图)之间。无论他们在哪里着陆,这些碎片都会以一条很长的窄窄的线下降,而空间站密度最大的部分则会走得最远。
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On the face of it, the chance of any of that debris hitting someone is low. For one thing, the world is mostly ocean. For another, even on land people are small and scarce compared with the available area. Nor, indeed, is anyone known to have been injured by re-entering debris since the space age began (though someone has been hit but not hurt). The risk of such injury cannot, however, be ruled out—and the chance of damage to property, which occupies a larger fraction of Earth’s surface than people do, is proportionately higher.
从表面上看,这些碎片击中某人的几率很低。首先,世界大部分是海洋。另一方面,即使是陆地上,与可能出现的区域相比,人既小又少。事实上,在太空时代开始后,也没有人被返回的太空碎片击伤(尽管有人被击中,但没有受伤)。然而,这种伤害的风险不可能被排除——而且,相对于人而言,在地球表面占据更大比例的财产,遭受损害的几率要高得多。
The way to eliminate such risks is controlled re-entry. As Jonathan McDowell, an astrophysicist at Harvard University, observes, that is becoming more common. Around 40% of rocket stages that end up in space, he says, can now restart their own engines and alter their orbits. Most satellites bigger than about five tonnes likewise come fitted with motors of their own. That allows their controllers to aim them more precisely when the time comes to dispose of them.
消除这种风险的方法是控制再次进入。正如哈佛大学天体物理学家乔纳森麦克道尔所观察到的,这种现象正变得越来越普遍。他说,最终进入太空的火箭大约有40%可以重新启动它们自己的引擎,并改变它们的轨道。大多数超过5吨的卫星同样也安装了自己的发动机。这使得到该除掉它们的时候,它们的控制器能够更精确地瞄准它们。
Tiangong-1 itself was probably supposed to have been guided into the remote southern Pacific Ocean, the dumping site of choice for superannuated space hardware, in 2013. But, says Dr McDowell, the station was kept on as an insurance plan, in case the launch of its successor, Tiangong-2, failed. In the event, Tiangong-2 reached orbit in 2016 without incident. Tiangong-1, meanwhile, stopped working—leaving its fate in the hands of the space-weather gods rather than its controllers on the ground.
“天宫一号”本身很可能是被引导到遥远的南太平洋,在2013年,它是废弃太空硬件的首选垃圾场。但是,麦克道尔博士说,该站作为一项保险计划被保留了下来,以防其继任者“天宫二号”的发射失败。在这次活动中,天宫二号在2016年顺利进入轨道。与此同时,天宫一号停止了工作——把它的命运交给了太空气象的神,而不是地面上的控制人员。
This article appeared in the Science and technology section of the print edition under the headline "What goes up..."
英文原文选自《经济学人》