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探访四个巨行星需要多少燃料?
(2010年2月10日)
前天上午,不知跟骏骏谈什么问题时,话题又转到了天文学上。
骏骏说:“When all the planets in our solar system line up, you can visit all of them in one trip.”
我同意他的说法:“That's right. When all the planets line up, the space probe doesn't need to fly this way and that way to visit them one by one. That will save a lot of fuel. If they haven't lined up, I am afraid the space probe won't have enough fuel to visit them all.”
骏骏接着我的话头问:“How much fuel does it need to visit all the planets when they line up?”
这可是个大难题,航天专家恐怕都要算半天吧?我只好说:“I have no idea. Where did you learn about visiting all the planets? In Bill Nye the Science Guy, or in books?”
骏骏也想不起来了:“Maybe both.”
我就提议:“Let's check the books first.”
于是我们把书架上骏骏读过的那二三十本关于天文学和太空探索的原版英语科普书都拿下来,一本一本地翻。
骏骏的注意力被其中一本很久没读的 My First Book About Space 吸引住了,忘了刚才的问题,自个儿读起来。我不想打扰他的雅兴,自行查找有谈论刚才那个问题的书。
还好,找到了一本 The Best Book of Spaceships。
读了里面关于各大行星连成一线时探访它们的部分,才发现我和骏骏的记忆都有误,不是八大行星全部连成一线,而是四大巨行星连成一线时。里面是这样说的:
Every 175 years, the giant planets Jupiter, Saturn, Uranus and Neptune line up. This means a spacecraft can visit all of them in one trip. Two space probes, Voyagers 1 and 2, travelled all the way to these planets. They sent back some of the most beautiful pictures we have ever seen -- of stormy orange and white clouds over Jupiter, volcanoes erupting on Jupiter's moons and the broad, flat rings around Saturn.
但是,这里也没有提到需要用多少燃料的问题。事实上,这个问题太专业了,科普书上不可能有答案。
骏骏问:“What can you do if you can't find the answer in books?”
我说:“We can surf the internet to find the answer.”
骏骏不太相信:“Can you really find the answer on the internet? What can you do if you can't find it there?”
我笑了笑,说:“Since the Voyagers have already made the trips, I think there will be an answer on the internet. If you still can't find it on the internet, you will have to ask a space scientist.”
那天我们家的手提电脑被骏妈带去值班了,在家里没法上网,因此就不能够马上给他演示上网找信息的方法。
骏骏见我无可奈何,自己歪着脑袋想起来,过了一会儿又掐手指数数,然后告诉我:“They need 19 tonnes of fuel.”
我觉得有趣,问他:“How do you figure out that they need this much of fuel?”
骏骏说:“I don't know.”然后又问我:“Daddy, how much fuel does Deep Space 1 need?”
“深空一号”是新一代探测器,使用的是最先进的氙离子推进系统,我也不知道需要多少燃料。
我只好说:“Wait until I surf the internet.”
骏骏可不想等,他又自己思考起来,然后告诉我:“It needs 16 tonnes of fuel.”
我就问他:“Why should Deep Space 1 need less fuel? Shouldn't it fly further away from earth?”
骏骏想了想,又改口说:“Maybe 60 tonnes.”
哈哈,胡思乱想的小家伙!不过我还是鼓励他:“That's a good guess!”
昨天回到单位,我上网查了查需要多少燃料,结果 Google 不到答案。虽然晚上回去后,骏骏没再提那两个问题,但我心里却象压上了两块石头。 |
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