NASA's twin probes reach lunar orbit

 　　WASHINGTON, Jan. 1 (Xinhua) -- Twin U.S. spacecraft to study the moon from crust to core put themselves into the lunar orbit on New Year's Eve and New Year's Day, the country's space agency said.

　　The second Gravity Recovery And Interior Laboratory, or GRAIL-B, reached its lunar orbit at 5:43 p.m. EST (2243 GMT) on Sunday, according to the National Aeronautics¹ and Space Administration (NASA).

　　The GRAIL-A started orbiting the moon at 5 p.m. (2200 GMT) Saturday.

　　The insertion maneuvers² placed the spacecraft into a near-polar, elliptical orbit with an orbital period of approximately 11.5 hours, NASA said.

　　Over the coming weeks, the GRAIL team will execute a series of burns with each spacecraft to reduce their orbital period to just under two hours. At the start of the science phase in March 2012, the twin GRAILs will be in a near-polar, near-circular orbit with an altitude of about 55 km.

　　"NASA greets the new year with a new mission of exploration," Administrator³ Charles Bolden said in a statement. "The twin GRAIL spacecraft will vastly expand our knowledge of our moon and the evolution of our own planet."

　　During GRAIL's science mission, the two probes will transmit radio signals precisely⁴ defining the distance between them. As they fly over areas of greater and lesser⁵ gravity caused by visible features such as mountains, craters⁶ and masses hidden beneath the lunar surface, the distance between the twin spacecraft will change slightly.

　　Scientists will translate this information into a high-resolution map of the moon's gravitational field.

　　The data will allow scientists to understand what goes on below the lunar surface and increase knowledge of how Earth and its rocky neighbors in the inner solar system developed into the diverse worlds we see today.

1 aeronautics   

n.航空术，航空学

参考例句：

• National Aeronautics and Space undertakings have made great progress.国家的航空航天事业有了很大的发展。
• He devoted every spare moment to aeronautics.他把他所有多余的时间用在航空学上。

2 maneuvers   

n.策略，谋略，花招( maneuver的名词复数 )

参考例句：

• He suspected at once that she had been spying upon his maneuvers. 他立刻猜想到，她已经侦察到他的行动。 来自辞典例句
• Maneuvers in Guizhou occupied the Reds for four months. 贵州境内的作战占了红军四个月的时间。 来自辞典例句

3 administrator   

n.经营管理者，行政官员

参考例句：

• The role of administrator absorbed much of Ben's energy.行政职务耗掉本很多精力。
• He has proved himself capable as administrator.他表现出管理才能。

4 precisely   

adv.恰好，正好，精确地，细致地

参考例句：

• It's precisely that sort of slick sales-talk that I mistrust.我不相信的正是那种油腔滑调的推销宣传。
• The man adjusted very precisely.那个人调得很准。

5 lesser   

adj.次要的，较小的；adv.较小地，较少地

参考例句：

• Kept some of the lesser players out.不让那些次要的球员参加联赛。
• She has also been affected,but to a lesser degree.她也受到波及，但程度较轻。

6 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》