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俄火星探測器將于周日墜入地球
Russian spacecraft to crash to Earth on Sunday

[ 2012-01-13 15:30]

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Tthe Zenit-2SB rocket with the Phobos-Ground probe blasts off from its launch pad at the Cosmodrome Baikonur, Kazakhstan.(Agencies)

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The remainder of the crippled Phobos-Grunt spacecraft is set to crash to Earth on Sunday following its botched mission to Mars, space experts have said.

The minibus-sized Russian craft has been in a low orbit around Earth since losing contact with engineers shortly after its launch on November 8.

It had been intended to explore Phobos, one of Mars's two moons, but became stranded while still orbiting Earth and attempts to put it back on its original course failed.

Most of its mass is expected to burn up as the craft re-enters the atmosphere but 20 or 30 pieces of small debris collectively weighing about 200kg could reach Earth.

In a normal re-entry about 20 per cent of the space junk's mass would be likely to reach Earth, but in the case of Phobos-Grunt it could be even less because it contains large quantities of unused fuel which will burn or dissipate in the atmosphere.

In theory the remains could land anywhere south of Watford or north of the Falkland Islands, with a sea landing most likely due to the size of the oceans relative to the continents.

But scientists said observers would be unlikely to even see the debris crash to Earth unless it flew directly overhead in a clear sky, and that the chances of anyone being injured were absolutely minute.

Prof Richard Crowther of the UK Space Agency said: "The chances are so low – it certainly doesn't keep me awake at night worrying about the probability of a piece of space debris coming through my roof."

He added, however, that international space agencies need to discuss the amount of disused equipment being left in Earth's orbit amid fears space junk could reach a "critical mass" where damaging collisions with active satellites and space craft become inevitable.

The craft will explode on its descent meaning any material reaching the ground could be spread over an area measuring 200km long and 20km wide, and many pieces will be so small they would be hard to spot on the ground.

British experts based at RAF Fylingdales in North Yorkshire will monitor the craft as it descends but even as it begins its last orbit, 90 minutes before it arrives, they will only be able to predict its landing spot with an uncertainty of 4,000km.

(Read by Emily Cheng. Emily Cheng is a journalist at the China Daily Website.)

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(Agencies)

航天專家日前表示，“福布斯－土壤”火星探測器發(fā)射失敗后，報廢的航天器碎片將于周日墜入地球。

在去年11月8日發(fā)射后不久，這個面包車大小的火星探測器就與技術人員失去了聯(lián)系，進入環(huán)繞地球的低軌運行。

這個探測器原本是用來探測火衛(wèi)一的，火衛(wèi)一是火星的兩顆衛(wèi)星之一。但是探測器升空后一直處于地球軌道，變軌的努力也失敗了，導致計劃擱淺。

探測器大多數(shù)的碎片都會在再次進入大氣層時燃燒殆盡，但其總重約200公斤的20到30個小型殘骸將墜入地球。

通常情況下，探測器再次進入大氣層時，約有20%的太空垃圾可能會到達地球，但是“福布斯-土壤”帶來的太空垃圾可能會更少，因為這個探測器攜帶了大量未用燃料，燃料會在大氣層中燃燒或消散。

理論上看，殘骸可能會落在沃特福德以南或福克蘭群島以北的任何地方，但因為這一地區(qū)海洋面積比陸地面積大得多，殘骸最有可能墜入海中。

但科學家稱，觀測者可能連殘骸墜入地球也無法看到，除非殘骸在晴朗的天空從人們頭頂飛過，而且人們因殘骸墜落而受傷的幾率微乎其微。

英國航天局的理查德?克勞塞教授說: “這種幾率太小了，我當然不會晚上睡不著，擔心航天器的殘骸會砸透我的房頂”。

然而，他補充道，各國航空局需要討論一下遺留在地球軌道中的廢棄材料，以免太空垃圾達到“臨界質量”，對正在運行中的衛(wèi)星和航天器造成不可避免的破壞性碰撞。