[listen to sound of plane landing]
[飞机降落声]
That is the sound of the United States Air Force's unmanned spacecraft landing at the Kennedy Space Center in Florida over the weekend.
这就是美国空军的无人驾驶空天飞机周末在佛罗里达州肯尼迪航天中心着陆的声音。
The United States Department of Defense posted a video of the landing on YouTube.
美国国防部在YouTube网站上发布了着陆视频。
The Air Force's X-37B spacecraft passed over the state of Florida early in the morning Sunday.
周日一大早，美国空军的X-37B空天飞机从佛罗里达州上空掠过。
It made a different sound then. It created a "sonic boom." That is the noise caused by something traveling faster than the speed of sound – or 1,225 kilometers per hour.
那时它发出了一种不同的声音，它导致了音爆。音爆是指物体速度超过声速或1225公里每小时所造成的的噪音。
The sonic boom served as a surprising alarm clock for some Floridians. They took to Twitter to express their shock and describe the loud noise.
音爆成为了一些佛罗里达州人的意外闹铃。他们在推特上表达了他们的震撼，并描述了这种巨大噪音。
One person said she thought someone had crashed into her garage.
有人说，她还以为是有人撞入了她的车库。
The X-37B was first used in 2010. Each time it goes on a mission, it stays in space and orbits the Earth many times. In its first mission, it stayed in space for about six months. Its second mission was close to a year, and its third mission was close to two years.
X-37B空天飞机于2010年首次投入使用。每次执行任务时它都会在太空停留并绕地球轨道运行很多次。在第一次任务中，它在太空停留了大概6个月，第二次接近一年，第三次接近两年。
On Sunday, the plane ended its fourth mission about two weeks short of two years.
周日，这架空天飞机结束了第四次任务，停留了大约差两个星期到两年。
So, what does the plane do when it is in space?
那么，这架空天飞机在太空时都干了什么呢？
No one really knows. It is classified. That means only certain military members are permitted to know about its mission.
没人知道，因为这是机密。这意味着只有特定军人才了解其任务。
The Air Force can only publicly say that the plane helps them see how new devices perform while in space for a long time.
美国空军只能公开表示，这架空天飞机帮助他们弄清新设备在太空长期停留时如何运作。
The website Space.com reported that the Air Force was happy with the mission. The long trip did not result in any problems.
Space.com网站报道称，美国空军对这次任务非常满意。这次长途飞行没有发生任何问题。
The Air Force is planning to continue launching and landing the space plane from Florida.
美国空军计划继续从佛罗里达州发射和着陆这种空天飞机。
And that's what's Trending Today.
以上就是本期今日热点的全部内容。