它们主要是为低地球轨道设计的，在那里可以执行人类的任务。

They're primarily designed for Low Earth Orbit (LEO) where human-tended missions hang out.

“方舟天使”号现在进入地球轨道.

Ark Angel now entering Earth orbit.

进入地球轨道是昂贵的，也是疯狂的浪费。

Access to Earth orbit is expensive, and wildly wasteful.

在答复中，博尔登提及在轨道中建立燃料补给站的可能，这样小型火箭就可以实现低地球轨道的运行。

In response, Bolden referred to the possibility of setting up fuel depots in orbit, which could enable smaller rockets to make trips beyond low-Earth orbit.

虽然地球上方的空气在一定程度上阻止了那些位于低地球轨道上的太空垃圾高速撞向地球上，但由于相互摩擦也制造出不少洒向地球的金属碎片。

The problem: Whisper-thin traces of air gradually put the brakes on objects in low Earth orbit and create earthbound showers of hot metal bits.

地球轨道是并一直是难得的地点，成群的环绕卫星就是例证。

Earth orbit is and will remain a valuable place, as the swarms of satellites that circle the planet attest.

Starbrook是一个地面宽场光学传感器，能够测量高空地球轨道内数量上不断增加的物体，比如地球同步卫星和全球定位系统型轨道。

Starbrook is a ground-based wide-field optical sensor capable of surveying the increasingly large number of objects in the higher-Earth orbits, such as the geostationary and GPS-type orbits.

为了探索太阳和其它恒星的工作原理，在早期观测活动后，科学家使用火箭开始在地球轨道上对太阳进行研究。

To learn more about how the sun and other stars work, after early observations using rockets, scientists began studying the sun from Earth orbit.

它被设计为在低地球轨道进行测试，以便科学家可以看到分离，聚集各种技术，并与指挥和服务舱对接。

It was designed to be tested in low Earth orbit so scientists could see various techniques for separation, rendezvous, and dock with the command and service module.

欧洲航天局和其他国家都已经开始在讨论下一代空间站，以此作为一个基地，去探索超越近地球轨道之外的空间；

Esa and other nations are already discussing a next-generation space station that would operate as a base from which to explore space beyond low-Earth orbit;