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Every 26 months, Mars and Earth are at their closest distance, which is about 57 million kilometers apart.
每26个月，火星和地球之间的距离就会达到最小值：约5700万公里。
During this time, if an unmanned NASA spacecraft were to leave Earth,
在此期间，如果一艘无人驾驶的NASA宇宙飞船离开地球，
traveling at 58,000 kilometers per hour, it would take a little over 40 days to get to the Red Planet.
以每小时5.8万公里的速度飞行的话，40天出头就能到达那个红色的星球。
Not bad, right?
听着还不错，对吧？
Well, a quick trip would only be possible if the spacecraft followed a direct path, undisturbed by the wrath of the solar system and weight of life sustaining resources.
然而，只有当航天器沿着直线轨道飞行，不受太阳系风暴及维持生命的资源本身的负重的影响时，旅程才会最短。
Unfortunately, space travel is far more complicated than a straight line.
不幸的是，太空旅行比直线复杂得多。
So ideally, how long does it take to get to Mars?
那么，理想情况下，前往火星到底需要多长时间呢？
The solar system is constantly shifting, and the orbital mechanics behind each of the planets makes space travel really complex.
太阳系在不断发生变化，每个行星的轨道力学都会增加太空旅行的复杂性。
Because Earth and Mars have elliptical orbits, the distance between them varies considerably,
因为地球和火星的轨道都是椭圆轨道，两者之间的距离随时间差别很大，
and in order to send a spacecraft to Mars, the planets have to line up just right.
而且，要想将宇宙飞船送上火星，两个星球必须恰好位于一条线上。
It takes Earth one year to orbit the Sun, while it takes Mars about 1.9 years.
地球绕太阳公转一周需要一年时间，而火星需要1.9年左右。
So, every time Mars completes a single orbit, Earth goes around the sun almost twice.
因此，火星完成一次公转，地球要绕太阳几乎两周。
Historically, for NASA, the best launch window to Mars occurs every 2 years and 2 months or 26 months.
从历史来看，对于NASA来说，火星的最佳发射周期是2年零2个月，也就是26个月。
During this time, a spacecraft can utilize what is considered the most energy efficient path to Mars known as the Hohmann Transfer orbit.
在此期间，航天器可以沿所谓的最节能火星通道，即“霍曼转移轨道”飞行。
On this trajectory, the spacecraft follows an elliptical orbit around the Sun that intersects the orbit of Mars.
在这条轨道上，航天器能沿着围绕太阳并且与火星轨道相交的椭圆轨道飞行。
It uses fuel to increase speed and velocity to break free of Earth's gravity field.
通过燃料加快飞行速度和周转速度，从而摆脱地球的重力场。
And the spacecraft uses more fuel to decelerate in order to be captured into the Martian orbit.
然后航天器继续燃烧燃料来减速，以便切入火星轨道。
Then, it can ride Mars's orbital wave until it's ready to touch down on the surface.
之后就可以借着火星的轨道波飞行，直到准备好降落。
While the Hohmann transfer is considered the most efficient trajectory to get to Mars,
虽然霍曼转移轨道被认为是到达火星最有效的轨迹，
the journey is still estimated to take roughly 260 days or eight to nine months with a manned spacecraft powered by chemical propulsion,
据估计，使用化学推进装置的载人航天器还是大约需要260天，也就是8到9个月才能到达火星，
so NASA and private companies are trying to develop more efficient propulsion systems that can get humans to Mars faster than the chemical rockets used in the past.
所以，NASA和私营企业都在努力开发更有效，能够比过去使用的化学推进的火箭更快将人类送上火星的推进系统。
Specifically, a type of electric propulsion system that propels a spacecraft by accelerating a stream of electrically charged atoms, known as ions.
其中一种电力推进系统能够通过加速被称为“离子”的带电原子流来推进航天器。
And a nuclear thermal propulsion system that uses low-enriched uranium as its power source.
还有一种能够使用低浓铀作为动力源的核热推进系统。
But even if we do engineer a faster way to get to Mars, a round trip is still estimated to take multiple months.
然而，即便我们真的设计出了更快捷的登陆方式，往返估计也还是需要好几个月的时间。
And that means we also have to solve problems of human health and resource requirements during extended deep space missions.
这也就意味着我们在执行探索深空任务的同时，还要解决人类健康和资源需求方面的问题。
Clearly, time is just one of many obstacles standing in the way of our Martian dreams.
显然，时间只是阻碍我们实现登陆火星梦想的诸多障碍之一。
But still, NASA says it plans to send humans to Mars in the 2030s.
尽管如此，NASA仍然表示他们计划在2030年代将人类送上火星。
So do you think it's actually going to happen?
那么问题来了，你觉得到时候真的能够成功吗？
Let us know in the comments below and tell us what other obstacles you want us to explain.
请在下面的评论中告诉我们，并告诉我们您希望我们解释的其他障碍。
If you want to see more Space Crafts check out this playlist here.
想了解更多宇宙飞船方面的知识，请查看这边的播放列表。
And be sure to let us know in the comments what astronomical phenomena you want to learn more about.
还有，一定要在评论中告诉我们你们想了解的天文现象喔。
Thanks for watching Seeker! Don't forget to subscribe.
感谢大家收看我们栏目的视频！别忘了订阅喔。
