The amount of debris1 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.

美國(guó)上周四發(fā)布的一份報(bào)告稱，地球軌道上太空垃圾的數(shù)目已經(jīng)達(dá)到臨界點(diǎn)，有撞擊風(fēng)險(xiǎn)，而后可能產(chǎn)生更多碎片，威脅宇航員和人造衛(wèi)星的安全。

文中的tipping point就是指臨界點(diǎn)。Tip原意是指傾斜，翻倒，譬如弄翻了瓶子，就能說tip the bottle over。Tipping point（臨界點(diǎn)）有時(shí)也被翻譯成引燃點(diǎn)或轉(zhuǎn)折點(diǎn)，意思是進(jìn)步到一定量會(huì)產(chǎn)生某種質(zhì)的改變。

太空垃圾一般用space junk/debris來表示，其中包含defunct/ discarded satellite（報(bào)廢衛(wèi)星）、spent rocket bodies（火箭殘�。┑鹊龋�一般在low-Earth orbit（近地軌道）運(yùn)行�，F(xiàn)在國(guó)內(nèi)也在加緊研究manned space mission（載人航天計(jì)劃），并將發(fā)射天宮一號(hào)。