中国太空网

Rare Dolphin Seen in China, Experts Say

BEIJING, Aug. 29 (Reuters) — A Chinese man has videotaped a large white animal swimming in the Yangtze River that experts say is a member of a dolphin species unique to China and feared extinct, the official Xinhua news agency said Wednesday.

The last confirmed sighting of a member of the species, the long-beaked, nearly blind baiji, was in 2004. After an international team failed to find a single dolphin on a six-week expedition along the Yangtze last year, the species was classified as critically endangered and possibly extinct. But the videotape from central Anhui Province may renew slim hopes for the survival of the creature, also known as the white-flag dolphin.

“I never saw such a big thing in the water before, so I filmed it,” Zeng Yujiang, who spotted the dolphin, told Xinhua. He said it was about 1,000 yards away and “jumped out of water several times.” Wang Kexiong, of the Institute of Hydrobiology of the Chinese Academy of Sciences, said the institute had confirmed that a baiji was on the videotape.

In the late 1970s, scientists believed several hundred baiji were still alive, but by 1997 a survey listed just 13 sightings. Found only in the Yangtze, the baiji is related to freshwater dolphin species found in the Mekong, Indus, Ganges and Amazon Rivers.

China has set up a reserve in a lake in Hubei Province but has found no baiji to put in it.

Space station crew does construction work

CAPE CANAVERAL, Florida (Reuters) – Crew members on the International Space Station donned yellow construction helmets on Thursday and used a robotic crane to move a passageway for visiting spaceships and connecting modules.

The work was the most extensive assembly work on the $100 billion space station attempted by the station’s resident crew, without the help of visiting shuttle astronauts.

"Let’s fly," said station commander Fyodor Yurchikhin as flight controllers at the Johnson Space Center in Houston told him to start moving the robotic arm.

Yurchikhin was assisted by flight engineers Clay Anderson and Oleg Kotov. All three men wore yellow hats adorned with a sticker of their crew patch while they took turns operating the crane to relocate the docking bridge.

The hats were gifts from the crew of the shuttle Endeavour, who left the station and returned to Earth last week.

Work was interrupted twice by alarms indicating the 8-foot (2.4-metre), cone-shaped docking port adapter was not fully unlatched. Flight controllers determined the alarms were faulty and told the crew to press ahead.

The relocation of the adapter will clear a space for the shuttle Discovery crew to install a new connecting hub to the outpost in a mission slated for launch on October 23.

That hub, called Harmony, will be the doorway to Europe’s Columbus laboratory module and Japan’s Kibo complex. NASA hopes to install Columbus in December and Kibo during three missions next year.

The U.S. agency needs to fly at least 11 more shuttle flights to complete space station construction by 2010 when the shuttles are to be retired.

While the station crew worked in orbit, another construction mission was under way at the Kennedy Space Center in Florida. Technicians were modifying a fuel tank set to fly on Discovery to avoid a minor but time-consuming problem that occurred during Endeavour’s flight this month.

A piece of foam insulation flew off Endeavour’s tank during the shuttle’s launch on August 8, striking the underside of the ship and damaging two heat-resistant tiles.

NASA considered repairing the damage during a spacewalk, but ultimately determined Endeavour would be safe to fly through the atmosphere for landing without modifications.

X-rays on the tank slated to fly on Discovery showed cracks in an underlying layer of insulation. NASA decided to remove and replace the foam in four areas affected by the damage and expects no delays in Discovery’s launch.

Fuel tank foam insulation has been a big issue for NASA since a chunk broke off during the ill-fated flight of shuttle Columbia in 2003. The spacecraft was destroyed and its seven astronauts killed after its heat shield was damaged by the falling foam.

美国观测到首例地外星体强降水现象

新生原恒星上有超音速降落的冰雹

        据国外媒体8月30日报道，近日，美国宇航局研究人员声称，现探测到一颗距离地球数千光年的原恒星，这颗处于胚胎阶段的原恒星出现大量的降水，这是迄今科学家发现的首例地外星体降水现象。

这颗诞生于灰尘和气体之间的新生恒星充满了神秘色彩，研究人员发现该星体上的降水量相当于地球海水总体积的5倍之多。最初这些水分子是以冰雹形式存在，以超音速速度从上空降落。他们通过模拟实验称，这些冰雹降落在满是灰尘的原恒星上，正值该星体的胚胎成长期。纽约罗彻斯特大学天体物理学家丹•沃森说，“这是我们第一次观测到地外星体出现降水现象。”沃森所负责并撰写的这项研究报告发表在8月30日出版的《自然》杂志上。

这项研究工作是基于美国宇航局斯皮策空间望远镜对胚胎星系的最新观测资料，由于可见光很容易被原恒星灰尘环境吸收，人的肉眼无法观测，因此，天文学家通过红外线光谱观测诸如此类的原恒星。观测结果显示，在红外线中出现一种由水蒸汽形成的与众不同的光谱。

这颗原恒星距离地球数千光年，处于气体和灰尘云团之中。研究人员现将这一整个星系命名为NGC 1333-IRAS 4B，或简称为IRAS 4B。

IRAS 4B是一颗温暖的星体，其围绕的云团中富含水分子，它的直径大约为36亿英里（58亿公里），远大于冥王星与太阳之间的距离。基于所掌握的数据，沃森和同事们称，这颗原恒星的表面温度大约为零下103摄氏度。

沃森解释称，与地球相比，这颗原恒星的温度比地球低许多。其大气层水分子的气压特性有显著特征，这些水分子所承受的大气压只有地球零海拔的十亿分之一。此外，每年原恒星上的降水相当于地球降水量的23倍。他还指出，降水使这颗原恒星很潮湿，该星系的蓄水量要大于整个太阳系。

美国宇航局研究员使用斯皮策空间望远镜对30颗胚胎星系进行了观测，结果显示只有IRAS 4B存在水蒸汽迹象。沃森强调称，这很可能是由于IRAS 4B这颗原恒星轴线方向朝向地球，也许其他29颗原恒星比IRAS 4B的水量还要多，但是它们的轴线方向使我们无法仔细观测其星体。

目前，研究小组已探测到数百颗像IRAS 4B的原恒星，并计划使用斯皮策空间望远镜进行观测，其中许多原恒星的轴线方向各异不一致。

新型太空望远镜6年后将取代哈勃

波阵面传感控制能将18面镜片调整为最佳位置

韦伯的聚光能力将比哈勃强近6倍

        据国外媒体8月30日报道，工程师在8月26日举行的照片光学仪器工程师大会上表示，他们已经成功测试了新一代太空望远镜詹姆士-韦伯（JWST）的镜片控制“大脑”。此大脑软件就是波阵面传感控制，简称WFSC。它将让韦伯望远镜调整其18面镜片。

“所有18面镜片排列的位置很关键，只有调整到位，它们才能组成一个平滑的表面，”美国宇航局戈达德太空飞行中心(GSFC)的系统工程师比尔·海登说，“这将让科学家清楚地对准他们现在不能看到的非常暗淡的天体。”

哈勃的对手

韦伯将在2013年取代"哈勃"望远镜，继续执行巡天观星的任务。韦伯的长宽高分别为24米、12米、12米，体积约为"哈勃"望远镜的3倍。而且，与"哈勃"望远镜相比，韦伯的设计有了很大提高，六边型主镜片的直径约为6.5米，"哈勃"只有2.4米。韦伯18面镜片组成25平方米的大镜片，而哈勃大镜片只有4.3平方米，相比之下，韦伯聚光能力比哈勃强近6倍，而且，韦伯如此巨大的镜片使得它能够探测到亮度很低的天体，而"哈勃"所能探测到的天体亮度是它的400倍。天文学家期望韦伯能看到最初的星星和星系，还有年轻的行星系统。

韦伯将以折叠形状进行发射，在发射升空后，镜片才会在距离地球160万公里的位置上全部打开。此外，一个面积如网球场的矩形5层遮阳板也将被展开，用来为镜片和其它航天器元部件遮挡来自太阳的热量。如果不对其展开的镜片进行调整，当它首次进入太空时，它拍摄的图片会很模糊，像哈勃一样。

鲍尔航空技术公司总裁兼首席执行官大卫·泰勒说，WFSC软件会防止这一问题出现，此软件是基于哈勃的同样软件代码基础上开放出来。“这是重大的技术进步，它是根据安装在哈勃与凯克望远镜上的软件程序进行开放的，”韦伯望远镜高级项目工程师约翰·麦瑟说。

迷你韦伯

为检测WFSC软件，工程师特地在实验室制造了一个六分之一大的迷你韦伯望远镜模型。真韦伯望远镜重达6.2吨，一旦进入太空，就会拍摄宇宙图片，并运行此软件来调整其18面镜片，之后用微型马达将它们纠正好位置。

在这次声明中，海登表示，此测试还没有完全结束，但不急于进行。“测试将在10月中旬开始，到12月初结束，最终测试将会非常成功，”海登说。