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The 4G mission is set to launch from Cape Canaveral in the United States on a space X Falcon 9 rocket in 2019.

4G 任务将于2019年从美国卡纳维拉尔角发射，搭载的是 space X 猎鹰9号火箭。

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So, let's say that you have a point in space at coordinates x, y, z.

有一个点位于由x, y, z轴确定的空间。

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The X-15 was the first major investment by the United States in manned space flight technology.

VOA: special.2010.07.07

They felt the X-15 could have continued to provide new information about aviation and space.

VOA: special.2010.07.07

Today,the X-15 hangs in the Air and Space Museum in Washington,D.C.

VOA: special.2010.07.07

In 1999, it deployed the powerful Chandra X-ray space telescope, with the first female commander at the helm, Eileen Collins.

CNN: NASA weighed retiring Columbia in 2001

This appears to be the mindset of the Air Force regarding its experimental X-37B space plane, the billion-dollar robotic vehicle's orbital flight being extended beyond the 270 days it was initially designed for.

ENGADGET: Air Force X-37B space plane books additional time on orbital cruise, orders another margarita

The agency has already spent billions of dollars on the National Aerospace Plane, the X-33, X-34, X-37, X-38 and the Orbital Space Plane.

FORBES: Magazine Article