Once it arrives at Mars,
当火星车到达火星时
the whole mass of the planet will stand in the way.
火星本身就会阻碍通信
Mars itself rotates as the Earth rotates,
火星也会和地球一样自转
and so sometimes, even if we wanted to talk to Curiosity,
某些时刻 尽管我们想与好奇号联系
we couldn't.
我们也不能
Because we just have the whole planet between us and Curiosity.
因为整个行星挡我们和好奇号之间
A Martian day lasts 24 hours and 40 minutes.
火星一日有24小时40分钟
For half of that time,
其中一半时间
the rover will drop behind the red planet's horizon,
火星车将处在火星地平线之下
out of view of Earth's antennas.
远离地球天线的接收范围
When Curiosity arrives,
当好奇号抵达时
night will be falling on Mars.
降落点正好迎来夜晚
Midway through its perilous landing procedure,
在十分危险的着陆过程中
the team will lose direct contact with the spacecraft.
控制团队将失去与航天器的直接联系
But NASA can rely on help
但是美国宇航局可以依靠
from some previous Mars missions.
以往的火星任务来提供帮助

重点解释：

1.arrive at到达

例句：I wish he would arrive at some conclusion.
但愿他会有一结论。

2.even if 即使；虽然

例句：Even if I fail this time, I would try again.
即使我这次失败了，我还要再试试。