Michael Slezak “Tiangong-1: Chinese space station will crash to Earth within months” https://www.theguardian.com/science/2017/oct/13/tiangong-1-chinese-space-station-will-crash-to-earth-within-months
中国は2011年に初の宇宙ステーション「天宮１号」を打ち上げているが*1、「天宮」は2016年９月頃から制御不能となっており、2017年10月から2018年４月までの間の何時かに大気圏内に再突入し、地球に激突すると言われてきた*2。 しかしながら、最近の観測によると、地球激突は数か月早くなる見込みだという。「 天宮１号」の重さは8.5頓だが、大気圏再突入の際に殆どは燃えてしまい、燃え残りとして地表に激突するのは100kg程度であるという。
過去の宇宙船の地球激突について。蘇聯と米国；
In 1991 the Soviet Union’s 20-tonne Salyut 7 space station crashed to Earth while still docked to another 20-tonne spacecraft called Cosmos 1686. They broke up over Argentina, scattering debris over the town of Capitán Bermúdez*3.Nasa’s enormous 77-tonne Skylab space station came hurtling to Earth in an almost completely uncontrolled descent in 1979, with some large pieces landing outside Perth in Western Australia*4.
*1:See Tania Branigan and Ian Sample “China unveils rival to International Space Station” https://www.theguardian.com/world/2011/apr/26/china-space-station-tiangong Stuart Clark “China: the new space superpower” https://www.theguardian.com/science/2016/aug/28/china-new-space-superpower-lunar-mars-missions
*2:See Tom Phillips and Bonnie Malkin “China's Tiangong-1 space station 'out of control' and will crash to Earth” https://www.theguardian.com/science/2016/sep/21/chinas-tiangong-1-space-station-out-of-control-crash-to-earth “Note verbale dated 4 May 2017 from the Permanent Mission of China to the United Nations (Vienna) addressed to the Secretary-General” http://www.unoosa.org/res/oosadoc/data/documents/2017/aac_105/aac_1051150_0_html/AC105_1150E.pdf
*3:See eg. https://en.wikipedia.org/wiki/Salyut_7 https://ja.wikipedia.org/wiki/%E3%82%B5%E3%83%AA%E3%83%A5%E3%83%BC%E3%83%887%E5%8F%B7 “Salyut-7 heads for crash-landing ..” https://www.newscientist.com/article/mg12917540-900-salyut-7-heads-for-crash-landing/
*4:See eg. Emma Wynne “When Skylab fell to earth” http://www.abc.net.au/local/photos/2009/07/09/2621733.htm Elizabeth Hanes “The Day Skylab Crashed to Earth: Facts About the First U.S. Space Station’s Re-Entry” http://www.history.com/news/the-day-skylab-crashed-to-earth-facts-about-the-first-u-s-space-stations-re-entry https://en.wikipedia.org/wiki/Skylab https://ja.wikipedia.org/wiki/%E3%82%B9%E3%82%AB%E3%82%A4%E3%83%A9%E3%83%96%E8%A8%88%E7%94%BB
