VOA标准英语2011--NASA's GRAIL to Map the Moon

NASA's GRAIL to Map the Moon

The U.S. space agency NASA is preparing to launch a new, nearly half-billion dollar lunar mission that will enable scientists to better understand the moon's gravitational field and the lunar interior, from crust to core. GRAIL, NASA's Gravity Recovery And Interior Laboratory mission, lifts off from Cape¹ Canaveral in Florida on Thursday.
The two solar-powered GRAIL spacecraft will spend more than three months approaching our moon, and they will be flying similar, but separate, trajectories² toward their target.
Ed Weiler, of NASA's Science Mission Directorate, explains GRAIL's goal once it reaches its destination.
"GRAIL, simply put, is a journey to the center of the moon," said Weiler. "It will probe the interior of the moon and map its gravity field 100 to 1,000 times better than ever before."
In essence, the washing-machine sized satellites will chase one another around the moon, about 200 kilometers apart, and use radio signals to determine the distance between them.
"As the first satellite goes over a higher mass concentration or higher gravity, it will speed up slightly, and that will increase the distance, and then as the second satellite goes over, that distance will close again," added Weiler.
In this tandem³ formation, the spacecraft will spend three months mapping the moon's gravitational field. NASA expects GRAIL to yield the most accurate gravity map of the moon to date.
Scientists will then compare gravitational and topographical maps of the lunar surface.
They explain that as the lunar shape varies, gravity varies, and they expect there to be a difference in the gravitational signal over lunar craters⁴ and mountains. If that is not the case, it will be a sign that something is going on in the moon's interior.
NASA says the insights gained from the GRAIL mission will help them better understand the way rocky planets, including Earth, formed. The gravitational map will also be an important navigational tool for future lunar spacecraft.
The GRAIL twins are due to arrive at the moon around January 1, 2012.

1 cape   

n.海角，岬；披肩，短披风

参考例句：

• I long for a trip to the Cape of Good Hope.我渴望到好望角去旅行。
• She was wearing a cape over her dress.她在外套上披着一件披肩。

2 trajectories   

n.弹道( trajectory的名词复数 )；轨道；轨线；常角轨道

参考例句：

• To answer this question, we need to plot trajectories of principal stresses. 为了回答这个问题，我们尚须画出主应力迹线图。 来自辞典例句
• In the space program the theory is used to determine spaceship trajectories. 在空间计划中，这个理论用于确定飞船的轨道。 来自辞典例句

3 tandem   

n.同时发生；配合；adv.一个跟着一个地；纵排地；adj.（两匹马）前后纵列的

参考例句：

• Malcolm's contract will run in tandem with his existing one.马尔科姆的合同将与他手头的合同同时生效。
• He is working in tandem with officials of the Serious Fraud Office.他正配合欺诈重案办公室的官员工作。

4 craters   

n.火山口( crater的名词复数 )；弹坑等

参考例句：

• Small meteorites have left impact craters all over the planet's surface. 这个行星的表面布满了小块陨石留下的撞击坑。 来自《简明英汉词典》
• The battlefield was full of craters made by exploding shells. 战场上布满弹坑。 来自《现代英汉综合大词典》