天宫一号掉哪儿了？| 卫报

Where will the out-of-control Chinese space station land?

What is happening with the Chinese space station?

中国空间站发生了什么？

The nation’s first prototype space station, Tiangong-1, or “Heavenly Palace”, launched into orbit in September 2011. The module reached the end of its service life earlier this year and was due to splashdown – eventually – in the Pacific Ocean. But at a recent press conference, the Chinese space agency  it had lost contact with the station. They did not explain what had gone wrong.

国家的第一个原型空间站天宫一号2011年9月发射升空。今年初，太空舱超过了使用寿命，计划坠海，最终落入太平洋。但最近一次发布会上，中国航天机构承认与空间站失去联系，未解释问题出在哪里。

Does losing contact matter?

失联重要吗？

It depends what the Chinese planned to do next. If the agency was going to let the spacecraft simply fall to Earth in an uncontrolled way and burn up in the atmosphere, then the loss of contact means little.

这要看中国人计划如何。如果打算让飞行器以失控的方式落入地球，在大气层燃烧，那么失联是无所谓的。

But if they had intended to perform a controlled de-orbit, that option is now gone. Controlled de-orbits tend to be reserved for spacecraft that pose a potential risk to people when they fall back to Earth.

但如果本计划实施有控制的离轨，那么现在已经无能为力了。有控制的离轨通常用于那些落回地球后对人们具有潜在危险的飞行器。

If the chances of someone being injured by components that survive the fireball of re-entry is greater than one in 10,000, then the spacecraft should be actively steered into a region of the South Pacific known in the business as the “”. The module is already below the altitude of the International Space Station (ISS) and so there is no risk of a collision on its way down.

如果有人被火球没有燃烧的部分伤害的可能性大于一万分之一，那么飞行器就该有控制地跌入南太平洋地区，业内称这里是“航空器坟场”。该太空舱高度已低于国际航空站，返回时不会导致相撞。

What was Tiangong-1 for?

天宫一号干什么的？

Unlike the massive ISS, which is the size of a football field and has the living space of a five-bedroom house, Tiangong-1 is a mere 10 metres long and 3 metres wide. The Chinese used the module to practise rendezvous and docking procedures, and several taikonauts, including two women, spent time aboard after catching a ride on the Shenzhou spacecraft.

与大块头国际空间站不同——国际空间站有足球场那么大，生活空间有五个卧室，天宫一号只有10米长、3米宽。中国人用这个太空舱练习交会和对接，几个太空员，其中包括两名女性，乘坐神舟飞船去太空舱居住了一阵。

Losing control of the module is more of an embarrassment to the Chinese space agency than a blow to their space programme. Two weeks ago, in a long-scheduled launch, the Chinese put another space station module, Tiangong-2, into orbit, and a crew of at least two taikonauts is expected to visit as early as next month. The agency still hopes to build a 55-tonne space station by 2020.

与太空舱失联让中国航天机构感到尴尬，对他们的太空计划却谈不上打击。两周前，中国将另一个太空舱天宫二号送入轨道，发射计划早就定好了。至少两名太空员有望在下月初访问天宫二号。航天机构希望到2020年建造一个55吨的空间站。

Will the stricken module survive re-entry?

生病的太空舱能不掉下来吗？

 show the Chinese module at 380km high and travelling at 27,500km per hour. At that speed and altitude, it could lap the planet 5,000 more times before it starts to feel the drag of the upper atmosphere and begin its final descent. Most of the 8.5-tonne module will burn up from aerodynamic heating in the Earth’s atmosphere.

卫星跟踪雷达表明中国的太空舱在380千米处，每小时27500千米。这个速度、这个高度，绕行地球5000圈后，开始感觉到上层大气的拉力，并开始最终的下降。8.5吨的舱体，大部将在大气层的气动加热中燃尽。

But the Chinese space agency has conceded that some heat-resistant components may survive. “The module is predominantly a hollow shell, so there’s a good chance a significant portion will burn up in the atmosphere. But there’s also a chance some elements will survive down to surface,” said Hugh Lewis, a space debris expert at University of Southampton.

但中国航天机构承认某些耐热部分会幸存下来。南安普敦大学空间垃圾专家Hugh Lewis说：“太空舱主要是个空壳，更有可能主要部分在大气中燃尽。但也有可能某些部分会落到地面上。”

Where will it come down?

落在哪里？

No one knows. And the vagaries of re-entry mean it will be impossible to predict with accuracy, even in its final moments. Computer simulations cannot tell far in advance on which orbit a spacecraft will re-enter. The Tiangong-1 is moving fast, at a shallow angle relative to the atmosphere, and the height of the atmosphere at any point depends on the regional temperature. 

没人说得好。返回变数意味着不可能精确估计到地点，即便在最后时刻。计算机模拟不可能提前算出航空器返回时的轨道。天宫一号移动很快，与大气层角度很浅，而任何一点的大气厚度都依赖于所处的温度。

But even when an object has begun its descent through the atmosphere, the final resting place of debris is still hard to predict. How the spacecraft tumbles through the atmosphere has an influence on how it breaks up. The most space agencies can do is calculate a debris ellipse where fragments are expected to land.

即便物体穿过大气开始坠落，最终残骸的栖息地也很难预计。宇航器穿过大气时如何翻滚对其如何解体有影响。宇航机构能做的最多不过是计算残骸可能着陆的椭圆区域。

Are we in danger?

我们有危险吗？

Pieces of space debris fall to Earth every day, but most of these are small fragments. Now and again, whole satellites or rocket stages tumble out of orbit and break apart in the sky. 

每天都有太空残骸掉落地球，大多数是小碎片。整个卫星或火箭的某段不时会脱离轨道，在天空中解体。

The most dangerous uncontrolled re-entry happened in 1979 when Nasa’s 85-tonne Skylab space station . In 2001, when the Russian Mir space station had reached the end of its life, Roscosmos de-orbited the 135-tonne outpost into the Pacific. But even with so much hardware raining from the skies, no one is known to have been hurt by falling space junk.

最危险的无控制返回发生在1979年，当时NASA重达85吨的Skylab空间站落入澳大利亚。2001年，而过的Mir空间站寿终正寝，俄罗斯联邦航天局让这个135吨的太空基地脱轨落入太平洋。但即便这么多硬货从天空中落下来，也没听说有人被太空垃圾砸到受伤。

The odds are wildly in favour of not being hit because most of the Earth’s surface is covered with water, and most of the world’s population is crammed into a small percentage of land. 

有极大可能性我们不会被砸到，因为大部分地球表面覆盖着水，世界大多数人口只挤在很小的一部分土地上生存。

The chances of a specific individual being struck by falling debris is trillions to one, making death by lightning far more likely.

某个人被掉落的残骸击中的概率是万亿分之一，相比而言，被雷劈死的可能性都要大得多。