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[林间]“潮起”和“潮落”重力双卫星撞月,结束使命

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jlinwhoi 发表于 2012-12-14 08:29:25 | 显示全部楼层 |阅读模式
本帖最后由 jlinwhoi 于 2012-12-18 18:54 编辑


图1.  Grail计划的重力双卫星:“潮起”和“潮落”。(来源:NASA,JPL;转载来源:http://www.google.com/hostednews ... 4a5ca3f&index=0

今年在上海、广州、青岛、兰州等地,我给同学们讲课时,多次谈到了美国最新的Grail重力双卫星怎么精确地测量月球的重力场。其主要原理是用激光连续地测量两卫星之间的精确距离,然后根据两卫星之间距离的变化来反演计算卫星飞过之处的重力场。

Grail计划耗资四亿多美金,其首席科学家是麻省理工学院的Maria Zuber教授。Maria也是MIT/WHOI Joint Program的教授,目前正和我一起指导JoyOcean网友丁忞同学的博士论文。Maria是我在布朗大学的师姐,她每年夏天来Woods Hole工作时,都共用我在WHOI的办公室。我还记得几年前,她在我的办公室写Grail卫星计划申请书时的情景。

Grail计划由两颗卫星组成,一颗叫“潮起”(英文为Flow),另一颗叫“潮落”(英文为Ebb)。卫星的名字是NASA通过大众征名,由美国一小学的学生们起的。2011年9月8日,在佛罗里达州的火箭发射场,一枚Delta II火箭将该双卫星送入了太空。作为Maria的朋友和同事,我们收到了JPL(喷气动力实验室)的邀请,去参观该双卫星的升空。可惜当时会议冲突,我没能到现场观摩火箭发射。

2012年1月1日,“潮起”与“潮落”进入了月球轨道,开始收集重力资料,一些重要的科学结果已经发表在2012年12月7日的《科学》杂志上(见:美探测器助专家绘制极精确月球重力场图 http://www.joyocean.org/bbs/viewthread.php?tid=2765

下周一,2012年12月17日,“潮起”和“潮落”双卫星就要结束它们近一年的绕月任务,按计划撞上月球北极附近的一座山脉。“潮落”将先撞,“潮起”20秒钟后也撞,它们的撞击速度将为每小时三千八百英里,约为喷气式飞机速度的八倍。

我很高兴能目睹Grail卫星计划的起源、诞生、和成功完成任务的过程。下周一,“潮起”和“潮落”就要结束它们的使命,撞上月球,化为灰烬,多少有点悲凉。

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 楼主| jlinwhoi 发表于 2012-12-14 08:48:31 | 显示全部楼层
以下报道来源于共同社(Associated Press)
(转载来源:http://www.google.com/hostednews ... 333831d65e7d4a5ca3f

Twin NASA spacecraft prepare to crash into moon

By By ALICIA CHANG, AP Science Writer

LOS ANGELES (AP) — After nearly a year circling the moon, NASA's Ebb and Flow will meet their demise when they crash — on purpose — into the lunar surface.

Just don't expect to see celestial fireworks. Next week's impact near the moon's north pole by the washing machine-sized spacecraft won't carve a gaping crater or kick up a lot of debris. And it'll be dark when it happens.

"We are not expecting a big flash or a big explosion" that will be visible from Earth, said mission chief scientist Maria Zuber of the Massachusetts Institute of Technology.

Still, it'll mark a violent end to a successful mission that has produced the most high-resolution gravity maps of Earth's closest neighbor. On Friday, engineers will turn off the science instruments in preparation for Monday's finale.

Previous unmanned trips to the moon have studied its lumpy gravitational field, but Ebb and Flow are the first ones dedicated to this goal. Since entering orbit over New Year's weekend, the formation-flying spacecraft have peered past the craggy surface into the interior.

Initially, the spacecraft flew about 35 miles above the surface and later dropped down to 14 miles. About an hour before Monday's impact, they will fire their engines until they run out of fuel and slam at 3,800 mph into a predetermined target — a mountain near the north pole that's far away from the Apollo landing sites.

Ebb will hit first followed by Flow 20 seconds later. Though the drama won't be visible from Earth, the Lunar Reconnaissance Orbiter will fly over the crash site afterward and attempt to spot them.

The last time NASA aimed at the moon was in 2009. The world watched through telescopes and over the Internet as a spacecraft and its booster rocket smashed into a permanently shadowed crater — a one-two punch that fizzled when spectators saw little more than a fuzzy white flash.

The mission's end will also mark the close of a student campaign that used cameras aboard the spacecraft to image lunar targets including on the moon's far side. The MoonKAM project was spearheaded by a science education company founded by Sally Ride, the first American woman in space. Ride died of pancreatic cancer in July at age 61.

Even after Ebb and Flow complete their mission, scientists will continue to pore over the bounty of data they collected.

Among their findings so far: The moon is more beat up than previously imagined. The crust is much thinner than thought. And there's no evidence that Earth once had two moons that collided to form the one we see in the night sky.”
周志远 发表于 2012-12-14 11:58:49 | 显示全部楼层
为什么要撞毁?设计的使用寿命到了?
小郭 发表于 2012-12-14 19:35:48 | 显示全部楼层
回复 3# 周志远

为何撞月?

  国际宇航科学院院士、中国空间技术研究院研究员朱毅麟介绍,嫦娥一号寿命即将到期,与其自然坠落,不如地面控制让它撞击月球。这样可以获得落月过程的一些控制经验,为探月工程二期实现软着陆做好技术储备。另外,也可以通过撞击的扬尘分析得到月球表面土壤的一些成分。从另外的意义上来说,撞击让月球表面第一次留下了中国的痕迹。
来自http://news.sohu.com/20091009/n267239965.shtml
NASA LCROSS撞月瞬间实时影像画面  http://news.sohu.com/20091009/n267239131.shtml
“嫦娥一号”卫星在控制下成功撞击月球。 http://news.163.com/09/0301/16/53B6SHO80001124J.html
同样做一件事情,两国的投入人员相差甚远,是技术已经成熟的原因么?
JO_Editor1 发表于 2012-12-14 21:04:25 | 显示全部楼层
nitzschia评论:cool
JO_Editor1 发表于 2012-12-15 00:36:10 | 显示全部楼层
minxu评论:撞上月球,太狠了,太不注意环保了,批评一下,嗯
JO_Editor1 发表于 2012-12-18 18:57:41 | 显示全部楼层
漫修兮评论:Thanks for intruducing.
 楼主| jlinwhoi 发表于 2012-12-18 19:06:20 | 显示全部楼层
本帖最后由 jlinwhoi 于 2012-12-19 00:45 编辑

“潮起”和“潮落”双卫星已于2012年12月17日格林威治时间22时28分(美国加州时间下午2时28分)撞上月球。撞击点在月球北极的一座山峰的南面,在Goldschmidt陨石坑的附近。撞击前五十分钟,两颗卫星打开发动机,将所有燃料烧完。

见如下报道:“NASA probes smash into moon”  http://www.tgdaily.com/space-fea ... bes-smash-into-moon

视频:“Twin Nasa spacecrafts crash-land on moon - video”  http://www.guardian.co.uk/scienc ... rashland-moon-video


This still image and animation shows the final flight path for NASA's twin Gravity Recovery and Interior Laboratory (GRAIL) mission spacecraft, which will impact the moon on Dec. 17, 2012, around 2:28 p.m. PST. Their successful prime and extended science missions now completed, the twin GRAIL spacecraft Ebb and Flow are being sent purposefully into the moon because their low orbit and fuel state precludes further scientific operations.

The animations were created from data obtained by NASA's Lunar Reconnaissance Orbiter. Image credit: NASA/JPL-Caltech/GSFC/ASU

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JO_Editor1 发表于 2012-12-21 01:05:43 | 显示全部楼层
lfan评论:黯然……巡天万里有穷日,潮起潮落无尽时。
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