经济学人下载:微型汽车大的探测器在火星着陆

Science and Technolgy
科技

Mars exploration
探测火星

How to land a Mini on Mars
如何让一辆微型汽车大的探测器在火星着陆

The biggest and fanciest Mars rover so far will soon blast off from Florida
迄今为止最昂贵、最大的火星漫游者将很快从佛罗里达发射升空

EARTH excepted, the most probed and prodded planet in the solar system is Mars. Besides the assortment of craft that have flown by it or gone into orbit around it, three robotic buggies equipped with cameras and scientific instruments have roamed the Martian surface on behalf of NASA, America's space agency, since 1997.
除了地球，火星是太阳系里被人类探索得最多、最让人感到刺激的行星。除了各种飞过它的以及进入它附近轨道的飞船外，从1997年开始，三个装配了相机和科学仪器的探险车已经代表美国太空机构NASA漫游了火星表面。

If all goes according to plan, they will soon be joined by a fourth. On November 26th a new rover, Curiosity, will ascend from Cape Canaveral. If it gets there in one piece, it will examine the climate and geology of Mars and look for any signs of life that might have arisen.
如果所有一切都按计划进行，第四个将探险车将很快加入其中。11月26日，新的漫游者"好奇号"将从卡拉维拉尔角发射升空。如果它完好无损地抵达，它将考察火星气候和地质，并寻找可能出现的生命迹象。

The first of NASA's rovers, Sojourner, which reached Mars in 1997, was 65cm long and weighed (on Earth, where the gravitational pull is 2? times Mars's) 10kg. Spirit and Opportunity, its twin successors, were larger, at 1.6 metres and 170kg. Curiosity, by comparison, is a monster. At 3 metres and 900kg it is the size of a small car. It also uses different technology. The other three rovers were powered by solar panels. Curiosity is powered by plutonium. (Not a full-scale reactor, but a generator that turns the heat of radioactive decay into electrical energy.) This brings three advantages. First, it allows Curiosity to carry more power-hungry scientific instruments than previous rovers. Second, it permits the rover to work through the Martian winter. Third, it avoids the problem of dust accumulating on the solar panels, which gradually sapped the strength of its predecessors.
1997年，NASA的火星漫游者"旅居者"到达火星，它长65厘米，重10千克（地球引力是火星的2.5倍）。其继任者，双胞胎"勇气和机遇号"比它更大（1.6米、170千克）。相比之下，"好奇号"就是个怪物。其3米长、900公斤重的尺寸就像一部小汽车。它也有不同的技术，之前漫游者由太阳能面板提供能量，"好奇号"由钚驱动（不完全是反应堆，而是一个将放射衰变产生的热能转换成电能的发电机）。这有三点好处：1、比起之前的漫游者，它能让"好奇号"带上更多的能耗大的科学仪器；2、它允许漫游者在火星冬季保持运转。3、它能避免让前几个漫游者的能量逐渐损耗的太阳能面板积土问题。

Curiosity's size makes getting it safely onto the Martian surface tricky. Previous rovers have deployed parachutes to slow their descents, and have then crashed into the ground using airbags to cushion their impacts. Curiosity is too massive for that approach to work. Instead, NASA hopes to deposit it on Mars using a contraption it has dubbed a skycrane.
"好奇号"的尺寸使之能在火星复杂表面安全着陆。以前，漫游者打开降落伞减慢下降速度，在撞向地面时用安全气囊缓冲。"好奇号"大到这样的方法不能起作用。相反地，NASA希望利用一种精巧的被称为"天空起重机"的装置使其在火星着陆。

As with the other rovers, Curiosity's mother ship will rely on heat shields and air-resistance, and then on a parachute, to slow its arrival. But at an altitude of 1.6km a specially designed descent stage bearing the rover will drop away from this vehicle. The descent stage has eight rocket motors on its corners. These will slow its fall to a relatively sedate 0.75 metres a second. When it is about 20 metres above the surface, the rover will be lowered from it on wires and deposited gently onto the Martian landscape. The cables will then be cut with explosives, the descent stage will fly off and crash land elsewhere, and Curiosity will begin its mission.
像其它几个漫游者一样，"好奇号"的母船将依靠隔热、耐大气摩擦的防护层，然后通过降落伞减速。但在1600米高时，一个特别设计的背负着漫游者的下降台从母船脱落，下降台的四角有8个火箭发动机，这些发动机把速度降到相对缓慢的0.75米/秒。离地约20米时，它将绑在线缆上的漫游者放下去，轻轻地在火星着陆。之后这些线缆将通过爆破切断，下降台飞走并在其它地方坠毁，"好奇号"开始它的任务。

That, at least, is the theory. But the skycrane has never been used before, and there is plenty else that could go wrong. Indeed, Mars has something of a reputation for destroying spacecraft. Around half the missions sent there since the first Soviet attempts in 1960 have failed to arrive. A conversation on the subject in 1964, between a journalist and John Casani, a NASA scientist, spawned the idea of a Great Galactic Ghoul, a malevolent creature that prowls the space-lanes between Earth and Mars, dining on unfortunate spacecraft.
这至少还是理论。除"天空起重机"从未用过外，可能出岔子的地方还有很多。火星有着宇宙飞船毁灭者的名声，自1960年苏联第一次尝试以来，约一半的登陆任务已经失败。1964年，NASA科学家约翰·卡萨尼与一名记者就这个问题有过一次对话，并得出了"星系食尸鬼"的概念——一个险恶的、徘徊在地球与火星之间航线的、以不幸的宇宙飞船为食的家伙。

The ghoul's latest victim appears to have been Phobos-Grunt, an ambitious Russian mission that was intended to return to Earth with a rock sample from Phobos, the larger of Mars's moons. The Russian space agency's engineers lost contact with it soon after its launch on November 8th. Limited contact had been re-established as The Economist went to press, but it is not clear whether the mission can be salvaged. NASA's engineers, rationalists though they be, will be keeping their fingers crossed on Saturday, and hoping that the ghoul's appetite has thus been sated, and that it will leave Curiosity alone.
最近一个亡于"食尸鬼"的似乎是俄罗斯的"福布斯—土壤"。一个雄心勃勃的打算把火星较大一颗卫星——火卫一的岩石标本带回地球的任务。11月8日，在发射不久，俄罗斯太空机构的工程师与它失去了联系。本刊截稿时，他们已经重新建立起有限的联系。尽管是理性主义者，NASA的工程师还是会在周六祈祷，希望"食尸鬼"的胃已经填饱了，而不去理睬"好奇号"。