（再说一个聆听大自然声音的故事。） 杜甫名句：锦城丝管日纷纷，半入江风半入云。此曲只应天上有，人间能得几回闻？说的是天子之乐，民间怎能擅用？ 但是，自然界中确实存在着 只应天上有 的宇宙之音。美国 Kronos Quartet 乐团演奏的 Sun Rings （《太阳鸣奏曲》），就是根据 Iowa 大学的著名空间物理学家 Don Gurnett 教授从事空间探索 40 年来从一系列人造卫星和人造行星（从最早的 Pioneer 10 ， 11 到已经飞到太阳系边缘的 Voyager 1 ， 2 ）的仪器上探测到的地球和外行星周围磁层的哨声波（ Whistler Waves ）和合声波（ Chorus Waves ）编谱的。真正的 此曲只应天上有 ！ 但并非 人间能得几回闻？ 2008 年美国物理学会的年会上， Don Gurnett 教授就放了地球、土星、木星等几个星球的 Chorus Waves 的录音。用他的话说： Chorus waves sound like a dawn chorus of chirping birds ：音频的合唱波（或者翻译成乐团波？）听起来像一群啁啾轻唱的小鸟的晨曲合声。。。 播放这几曲行星之音的时候， Gurnett 教授的 PPT 显示着他 17 岁时做高中科研时为一颗卫星研制一个信号接收仪器的照片。当年笔者到 Iowa 大学工作的时候， Gurnett 教授就已经白发苍苍了。但从他早年照片充满稚气的脸上，仍然可以找到如今容颜的一些影子。而更相像的，是他 17 岁时脸上充满对宇宙和未来的憧憬与在讲坛上聆听 Chorus Waves 的太阳鸣奏曲时专心致志的神态。。。 这些来自宇宙空间的乐曲，可以在 Gurnett 教授的 website 找到： http://www-pw.physics.uiowa.edu/space-audio/index.html 并附有下述说明： This is a sampling of some of Professor Don Gurnett 's favorite sounds of space. These sounds were recorded by University of Iowa instruments on a variety of spacecraft over the past 40 years and include audio samples provided to Terry Riley and the Kronos Quartet for their work Sun Rings . The multimedia production Sun Rings is based on sounds of space collected by University of Iowa Prof. Don Gurnett over a 40-year period. The musical portion of Sun Rings was composed by Terry Riley and performed by the Kronos Quartet, and accompanied by a visual production created by visual designer Willie Williams. Download and enjoy them! J
以下资料说是 : 国际重力界期盼已久的 GOCE 卫星 , 要在这个月发射 . 由于等米 (----GOCE 获取的实际数据 ) 下锅 , 众多研究者已经消磨了些许时光 , 处理 GOCE 获取的重力梯度 ( 重力位的二阶导数 ) 的软件已经有 N 种 . 只要数据有了 , 相信会引发一个股论文潮 . 不会再总是以模拟数据进行模拟计算了 , 这样的结果才让人更兴奋 . 实测数据将检验以下三个 预期结果 : 以毫伽 (1 mGal (1 mGal = 10 5 ms 2 ) ,ms 2 即米 / 秒的平方 ) 的精度确定重力异常 . 以 1 -2 厘米 的精度确定大地水准面 . 实现 100 公里 的空间分别率 . 以下资料来自欧洲空间局网站 http://www.esa.int/esaLP/ESAYEK1VMOC_LPgoce_0.html ESA's gravity mission GOCE Planned for launch in March 2009, ESA's Gravity field and steady-state Ocean Circulation Explorer (GOCE) has been developed to bring about a whole new level of understanding of one of the Earth's most fundamental forces of nature the gravity field. Dubbed the 'Formula 1' of spacecrafts, this sleek high-tech gravity satellite embodies many firsts in terms of its design and use of new technology in space to map Earth's gravity field in unprecedented detail. As the most advanced gravity space mission to date, GOCE will realise a broad range of fascinating new possibilities for the fields of oceanography, solid Earth physics, geodesy and sea-level research, and significantly contribute to furthering our understanding of climate change. Although invisible, gravity is a complex force of nature that has an immeasurable impact on our everyday lives. It is often assumed that the force of gravity on the surface of the Earth has a constant value, but in fact the value of 'g' varies subtly from place to place. These variations are due to a number of factors such as the rotation of the Earth, the position of mountains and ocean trenches and variations in density of the Earth's interior. 橙色部分大意 : 尽管重力不可见 , 这种复杂的力 , 一直在 ( 难以估量地 ) 影响着我们的生活 . 人们常假定重力的数值恒定 , 其实它 ( 以 g 表示 ) 随空间的变化在奇妙地变化着 , 影响因素有地球的自转 , 山脉海沟的位置 , 以及地球内部密度的变化等 . GOCE to map gravity as never before Over its lifetime of about 20 months, GOCE will map these global variations in the gravity field with extreme detail and accuracy. This will result in a unique model of the geoid, which is the surface of equal gravitational potential defined by the gravity field crucial for deriving accurate measurements of ocean circulation and sea-level change, both of which are affected by climate change. GOCE-derived data is also much needed to understand more about processes occurring inside the Earth and for use in practical applications such as surveying and levelling. GOCE takes six simultaneous measurements of the gravity field Since the gravitational signal is stronger closer to Earth, the 'arrow-like', five-metre long GOCE satellite has been designed to cut through of what remains of the Earth's atmosphere at just 250 km above the surface of the planet. This low-orbiting spacecraft is the first mission to employ the concept of gradiometry - the measurement of acceleration differences over short distances between an ensemble of proof masses inside the satellite. GOCE is equipped with three pairs of ultra-sensitive accelerometers arranged in three dimensions that respond to tiny variations in the 'gravitational tug' of the Earth as it travels along its orbital path. Because of their different position in the gravitational field they all experience the gravitational acceleration of the Earth slightly differently. The three axes of the gradiometer allow the simultaneous measurement of six independent but complementary components of the gravity field. Although the gradiometer forms the heart of the satellite, to measure gravity there can be no interference from moving parts so the entire spacecraft is actually one extremely sensitive measuring device. Mission objectives to determine gravity-field anomalies with an accuracy of 1 mGal (where 1 mGal = 10 5 ms 2 ). to determine the geoid with an accuracy of 1 -2 cm . to achieve the above at a spatial resolution better than 100 km .
Orbit Characteristics The CHAMP satellite was launched with a Russian COSMOS launch vehicle on July 15, 2000 into an almost circular, near polar (i = 87) orbit with an initial altitude of 454 km. The design lifetime of the satellite system is 5 years. The 87 degree inclination is the maximum inclination which can be served from the Plesetsk cosmodrome. The reason for choosing an almost circular and near-polar orbit is the advantage of getting a homogeneous and complete global coverage of the Earth's sphere with orbit and magnetometer measurements, being important to resolve the gravitational and magnetic geopotentials. An advantage of the 87 orbit vs. a dawn-dusk sun-synchronous orbit is the local time variation of the satellite's ground track which is essential for all three scientific applications in order to enable the separation of constituents of periodic phenomena like tides and day-night variations. An initial altitude of about 454 km is chosen (a) to guarantee a multi-year mission duration even under severe solar activity conditions, (b) to account for the requirement imposed by the atmosphere/ionosphere application to look from the outside through the different atmospheric layers, i.e., an even higher altitude would be the optimum in this regard, and (c) because 454 km is the adequate altitude to observe the Earth's magnetic main field. From the gravity field's point of view an even lower initial altitude would be desirable. Due to atmospheric drag the altitude will decrease over the 5 years mission lifetime. As CHAMP will pass through the solar activity maximum in about 2001, the predicted natural decay depends on the magnitude of the actual solar activity cycle and may amount to more than 200 km or only 50 km within the 5 years.. Therefore at least one velocity change manoeuvre by the 40 mN thrusters cold gas was foreseen, correcting for orbit injection errors and rising or lowering the orbit of the S/C to guarantee a 5 years observation period above 300 km and some months of observation time below 300 km altitude towards the end of the mission. After 2 orbit changes in 2002 CHAMP will provide further highly valuable data for another 2-3 years from low altitude. The International Laser Ranging Service (ILRS at http://ilrs.gsfc.nasa.gov ) provides tracking from its global network of laser ranging stations to support the project. Launch The CHAMP satellite was launched from the cosmodrome Plesetsk (north of Moscow) aboard a Russian COSMOS launch vehicle. The launch took place on July 15, 2000 at 11:59:59.628 UTC. Plesetsk Cosmodrome The launch site Plesetsk is located 800 km north-east of Moscow and has historically been the most active launch site on earth, from which over one third of all launches ever realized took place. From this site a wide range of up to almost polar inclinations can be served. COSMOS Launch Vehicle The POLYOT Design Bureau, Omsk has manufactured the Cosmos launch vehicle for nearly 30 years. The two-stage booster burns unsymmetrical dimethyl hydrazine (UDMH) as a fuel and either nitric acid or nitrogen tetroxide (N 2 O 4 ) as the oxidiser. The first stage employs two 11 D614 (RD216) main engines, while the second stage relies on a single, restartable 11D49 main engine. The second stage also carries an independent propulsion system for coast and spacecraft deployment operations. Used only for low earth orbit missions, the Cosmos-3M has a demonstrated payload capacity of 1,500 kg to a low altitude, 51 inclination parking orbit. However, since 1988 all Cosmos-3M missions have originated from the Plesetsk Cosmodrome with inclinations of 66, 74, 83, 87 and SSO. Main characteristics of the COSMOS launch system: Launch facility: ground supported, stationary Total launch mass: 109 metric tons Payload mass: up to 1500 kg Payload orbits: 250 to 1700 km Total length of launcher: 32.4 m Core diameter: 2.4 m Launches: 700 Success Rate: 97.4 %
标签: 卫星
