太空垃圾數量已達“臨界點”

The amount of debris orbiting the Earth has reached "a tipping point" for collisions, which would in turn generate more of the debris that threatens astronauts and satellites, according to a US study released on Thursday.

NASA needs a new strategic plan for mitigating the hazards posed by spent rocket bodies, discarded satellites and thousands of other pieces of junk flying around the planet at speeds of 17,500 miles (28,164 kilomtres) per hour, the National Research Council said in the study.

The council is one of the private, nonprofit US national academies that provide expert advice on scientific problems.

Orbital debris poses a threat to the approximately 1,000 operational commercial, military and civilian satellites orbiting the Earth -- part of a global industry that generated $168 billion in revenues last year, Satellite Industry Association figures show.

The world's first space smashup occurred in 2009 when a working Iridium communications satellite and a non-operational Russian satellite collided 490 miles (789 km) over Siberia, generating thousands of new pieces of orbital debris.

The amount of orbital debris tracked by the US Space Surveillance Network jumped from 9,949 cataloged objects in December 2006 to 16,094 in July 2011, the National Research Council said.

The surveillance network tracks objects approximately 10 centimeters in diameter and larger.

Some computer models show the amount of orbital debris "has reached a tipping point, with enough currently in orbit to continually collide and create even more debris, raising the risk of spacecraft failures," the research council said in a statement released Thursday as part its 182-page report.

"The current space environment is growing increasingly hazardous to spacecraft and astronauts," Donald Kessler, the former head of NASA's Orbital Debris Program Office who chaired the study team, said in a statement.據美國上週四發佈的一份報告，地球軌道上太空垃圾的數量已經達到“臨界點”，有撞擊風險，而後可能產生更多碎片，威脅宇航員和人造衛星的安全。

美國全國研究委員會在報告中稱，美國宇航局需要制定新的戰略計劃，以減小火箭殘骸、報廢衛星、以及數千塊其它太空垃圾的危害。這些軌道太空垃圾時速高達1.75萬英里（28164公里）。

該委員會是一傢俬立的非贏利性國家科研機構，致力於爲科學難題提供專家建議。

衛星產業協會發布的數據顯示，太空垃圾對地球軌道上空的大約一千個運行中的商用、軍用、民用衛星構成威脅。全球衛星產業每年收入高達1680億美元。

全球首例空間撞擊發生在2009年，當時正在運轉的一個銥通信衛星和一個俄羅斯報廢衛星在西伯利亞上空490英里（789公里）處發生撞擊，產生了數千個新的太空垃圾。

美國全國研究委員會稱，美國空間監測網跟蹤並登記在冊的太空垃圾數量在2006年12月爲9949個，而在2011年7月就上升到了16094個。

該監測網的監測對象是直徑10釐米以上的太空垃圾。

美國全國研究委員會在上週四發佈的一份聲明中指出，根據某些計算機模型，太空垃圾的數量已經“達到臨界值，目前在軌的垃圾數量足以發生頻繁撞擊，並由此產生更多的垃圾碎片，從而增大損毀航天器的風險。”這份報告長達182頁。

研究小組負責人唐納德•凱斯勒在聲明中說：“目前的太空環境對飛行器和宇航員來說越來越危險。”凱斯勒曾擔任美國宇航局軌道垃圾項目辦公室負責人。