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全文摘自最新一期 “经济学家”杂志 Economist,

Seven minutes of terror

惊心动魄7分钟!

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THREE rovers have landed successfully on Mars, Sojourner, Spirit and Opportunity. All three American craft landed in the same way. A heat shield protected them from the fiery rigours of the initial entry into the Martian atmosphere. Then a parachute slowed them down further, in preparation for what was essentially a semi-controlled crash, with the rovers protected within a shell of airbags.

美国先后成功地将3个探测器送上了火星,它们分别是: “旅行者号”,“精灵号”和“机遇号”,且它们着陆的方式都一样。为了防止在进入火星大气层时受到炙热高温的影响全部采用了同一种防热罩。在着陆下降时每个探测器都配备了一个降落伞可以迅速将它们的速度减慢,为的是受气囊保护的探测器半控制的冲撞着陆做准备。

Once the whole assembly had bounced to a stop, the airbags were deflated and the robots trundled out to begin their missions. But those three rovers were comparatively small. Sojourner has a mass of just 10.5kg; the twin Spirit and Opportunity rovers were 185kg apiece. Things will be different on August 6th, when Curiosity, the latest rover to be sent to the Red Planet, arrives. It is a monster at 900kg—about the same as a Volkswagen Polo. That makes cushioning the impact with airbags impossible.

一旦整个着陆过程完成,气囊就会自动排气解除保护功能,机器人们就会滚动而出开始履行它们的使命。可这3个探测器的体积相对来说都不大。“旅行者号”的重量只有10.5公斤; 而另外两个号称是孪生姐妹的“精灵号”和“机遇号”探测器每个重量也不过185公斤。而86日发射的探测器就不同了,它就是“好奇者号”探测器,也是目前最新一代到达火星的探测器。它的体积庞大像个怪兽重达900公斤,差不多如大众的高尔夫轿车一样。像这种重量和体积的探测器是根本不可能靠缓冲气囊来抗击着陆撞击的。

Instead, NASA’s engineers plan to lower it with a device they call a skycrane. Like its sister rovers, Curiosity’s descent at 21,000kph (13,000mph) will first be slowed by a heat shield and then a parachute. At a height of 1.6km above the surface, a special descent vehicle, equipped with eight rocket motors on its corners, will fall away. Balancing on the rocket exhaust, the descent stage’s fall will be slowed to around 0.75 metres a second. At 20 metres from the ground, the rover itself will be winched down on cables and set gently onto the Martian regolith. The cables will be cut with explosives, the descent stage will fly off to crash-land elsewhere, and Curiosity will be ready to start its mission.

而美国国家航天局的工程师们打算用一个他们称之为太空起重机的装置给这个最新款的探测器减速,同它的姐妹们一样,“好奇者号”探测器的下降速度高达每小时21千公里(相当于13,000英里)先是用防热罩, 然后再采用降落伞降速。在距离火星表面1.6公里的高度,一个装有8个火箭驱动器的特别降落台会自动脱离,待火箭燃料耗尽后降落台会以每秒0.75米的速度缓慢下落。在距离地面20米处探测器会被几根电缆吊起然后慢慢地把它放在火星表层。通过爆破方式电缆被切断,降落台会飞离坠毁,接下来“好奇者号”就会待命准备开始它的使命了。

That, at least, is the plan. The skycrane was tested on Earth before Curiosity was launched, but this is the first time it has been used on an actual mission. If anything goes wrong the rover must be able to correct the problem itself, for Mars is far enough from Earth that radio signals take 14 minutes to travel back and forth. The entire descent, from orbit to the ground, will take seven minutes. That means by the time NASA’s engineers receive a signal that the rover has entered the upper layers of the Martian atmosphere, the rover will already be sitting on the ground—or else smoking in bits at the bottom of Mars’s newest, and most expensive, crater. Expect plenty of chewed fingernails.

那起码是计划.在“好奇者号”探测器发射前夕,太空起重机在地球上进行了测试。可这一装置还是第一次在实际探测使命中应用。如果发生任何偏差,探测器须能具备自身修复功能,因为火星离地球太远,信号需要14分钟才能往返地球。从轨道到地面着陆的整个降落过程需7分钟。那就意味着届时在工程师们收到探测器在进入火星大气层的信号时,探测器早已着陆了。

They’ve done it. Curiosity touched down at 05:14 GMT, bumping down to the surface at a nice and sedate 0.6 metres per second. When the signal came through, staff at the Jet Propulsion Laboratory hugged each other and punched the air. According to Charles Bolden, NASA’s administrator, who is holding a triumphant press conference, John Holdren, Barack Obama’s science adviser, “nearly threw up” with the stress and worry of it all. But everything seems to have gone off perfectly.

他们成功了。“好奇者号”在格林威治时间5:14分着陆,以每秒0.6米的速度漂亮、沉稳地碰撞到地面。当火箭推进器试验室的员工们收到这一信号时,全体人员都高兴得相互拥抱并兴奋地把拳头挥向空中。现任国家航天局负责人也是奥巴马的科学顾问查尔斯 。博顿在他主持举行的庆功会上讲:“我们 差点儿因为压力和担忧而放弃,但现在似乎一切进行的如此完美,我们可以如释负重了!”

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