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    Lockheed Martin has begun work on a successor to the supersonic Blackbird SR-71 spy plane.
    The unmanned SR-72 will use an engine that netbines a turbine and a ramjet(冲压式喷气发动机) to reach its top speed of Mach 6 - about 3,600mph (5,800km/h).   Like its predecessor1, the SR-72 will be designed for high-altitude surveillance but might also be fitted with weapons to strike targets.   Lockheed said the aircraft should be operational by 2030.   Jet engines   The SR-72 is being developed at Lockheed Martin's Skunk2 Works R&D centre in California that designed and built the original Blackbird.   That aircraft first flew in 1964 and was a mainstay of US Air Force spying and surveillance work until 1998. It typically flew at altitudes of 24,000m (80,000ft) and could reach speeds of Mach 3.   In a blogpost about the SR-72, Lockheed Martin said the aircraft would operate at similar altitudes but would fly far faster. At Mach 6 the plane could travel the 3,500 miles (5,500km) from New York to London in less than an hour.   While spy satellites can photograph enemy territory, the relatively3 long time it takes for them to be moved to a new orbit so they pass over a target can limit their usefulness.   By contrast, wrote Lockheed Martin, the SR-72 "would be so fast, an adversary4 would have no time to react or hide".   For the SR-72, Lockheed Martin is drawing on work done on the Falcon5 HTV-2 hypersonic technology vehicle. This is a test-bed for the futuristic technologies needed to support safe hypersonic flight and cope with the extreme conditions encountered by any object flying at such a speed.   For instance, on one test flight of the HTV-2, the aircraft hit a top speed of Mach 20 and its flight surfaces reached 1,927C (3,500F).   To reach Mach 6, the SR-72 will use an engine that acts like a normal jet turbine until speeds of Mach 3 are reached but which then operates like a ramjet to accelerate beyond that.   "Speed is the next aviation advancement6 to counter emerging threats in the next several decades," said Brad Leland, Lockheed Martin's hypersonic programme manager on the blog. "The technology would be a game-changer in theatre, similar to how stealth(秘密,鬼祟) is changing the battlespace today."
    1 predecessor      n.前辈,前任 参考例句:
    It will share the fate of its predecessor.它将遭受与前者同样的命运。
    The new ambassador is more mature than his predecessor.新大使比他的前任更成熟一些。
    2 skunk      n.臭鼬,黄鼠狼;v.使惨败,使得零分;烂醉如泥 参考例句:
    That was a rotten thing to do, you skunk!那种事做得太缺德了,你这卑鄙的家伙!
    The skunk gives off an unpleasant smell when attacked.受到攻击时臭鼬会发出一种难闻的气味。
    3 relatively      adv.比较...地,相对地 参考例句:
    The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
    The operation was relatively painless.手术相对来说不痛。
    4 adversary      adj.敌手,对手 参考例句:
    He saw her as his main adversary within the netpany.他将她视为公司中主要的对手。
    They will do anything to undermine their adversary's reputation.他们会不择手段地去损害对手的名誉。
    5 falcon      n.隼,猎鹰 参考例句:
    The falcon was twice his size with pouted feathers.鹰张开羽毛比两只鹰还大。
    The boys went hunting with their falcon.男孩子们带着猎鹰出去打猎了。
    6 advancement      n.前进,促进,提升 参考例句:
    His new contribution to the advancement of physiology was well appreciated.他对生理学发展的新贡献获得高度赞赏。
    The aim of a university should be the advancement of learning.大学的目标应是促进学术。

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