by Adam Cole

NASA worker： T-minus[倒计时用语] ten， nine， eight...

In November of 2011， the Mars Science Laboratory lifted off[发射]， carrying Curiosity， NASAs Mars rover[飞行器]， into space.

NASA worker： ...one， main engine start， zero and lift off of Curiosity.

And then in August... Allen Chen （NASA engineer）： Touchdown confirmed[确认]. Were safe on Mars.

During the eight months in between， Curiosity was bombarded[轰击] with lots of radiation[辐射]， high-energy protons[质子] thrown out by the sun and

galactic[银河的] cosmic rays[宇宙射线] slicing[像刀一样运动]

through the solar system from distant supernovas[超新星]. Here on Earth， the magnetic field and atmosphere[大气] shield[防护] us from most of this radiation. But out in the void[空间] of space， high-energy particles[粒子] would rip[撕破，割裂] into an astronauts DNA， slowly increasing the risk of cancer. Thats a problem for NASA and the handful of other private companies who have pledged[保证] to send humans to Mars.

For a long time， theyve tried to figure out just how much radiation an astronaut would experience on the journey. Enter Curiosity， handily[方便地] equipped with RAD， the Radiation Assessment[评估] Detector[探测器]. It was designed to gather radiation data on the surface of Mars.

Don Hassler of the Southwest Research Institute leads the RAD team.

Don Hassler： About two years before launch， we started to realize the fact that RAD was tucked[挤进] inside the belly of the spacecraft sort of in the same location that a future astronaut might be.

So they thought： Why not turn it on during space flight？ A few days after launch， RAD powered up and started collecting data. In the journal Science， the researchers announced that the bulk[大量] of the radiation—95 percent—was caused by galactic cosmic rays that we dont know how to shield against. Hassler says theres really only one way to minimize the damage caused by these rays.

Hassler： I think we just want to go quickly.

The shortest possible trip to Mars with current technology would take about six months. During that time， Hassler says an astronaut would experience about four times more radiation than people on the International Space Station， who would be partially[部分地] shielded by their proximity[接近] to Earth.

Hassler： An astronaut on ISS for， say， six months， you know， would receive on the order of maybe 80 millisieverts[（单位）毫西弗]， compared with the 330 that we receive on our way to Mars.

The average American is only exposed to six millisieverts every year. Three hundred and thirty millisieverts is enough to increase your cancer risk by about one and a half percent or so. Double that number for a round trip visit to Mars， and you quickly approach[接近] the limits recommended[推荐] by the National Council on Radiation Protection. But that doesnt discourage Robert Zubrin.

Robert Zubrin： Radiation is not a showstopper[干扰物].

Zubrin is the president of The Mars Society and author of The Case for Mars.

Zubrin： Its not something that the FDA注would recommend that everyone do， but， you know， were talking about a mission to Mars here.

Zubrin says there are plenty of other risks involved in a Mars mission， like can they even land， and those are risks that many would be willing to take. The average person already has about a 20 percent chance of dying from cancer. A 40-year-old astronaut， who dreams of setting foot on the red planet， might not care about bumping that number up[提高] a few percentage points. Zubrin： Theres no cause for delay， at least as far as radiation is concerned， and we should now set our course for Mars.

Scientists still have questions about radiation on Mars itself. They need more data to better understand the cancer risk for Mars settlers on the surface. But dont worry， Curiosity is working on that too.

美国国家航空航天局员工：倒计时，十、九、八……

火星科学实验室于2011年11月升空，将美国国家航空航天局（NASA）的火星车“好奇号”送入太空。

美国国家航空航天局员工：……一，主引擎启动；零，好奇号升空。

然后到了（2012年）8月……

陈友伦（美国国家航空航天局工程师）：确认着陆。我们安全抵达火星。

在这之间的八个月当中，大量辐射、太阳发出的高能量质子以及远方的超新星穿越整个太阳系投射过来的银河宇宙射线对好奇号进行了轮番轰炸。在地球上，这类辐射大多被磁场与大气层挡在外头。而在太空空间当中，高能量粒子会侵入宇航员的DNA，逐步增加人体患癌机率。这正是美国国家航空航天局以及其他几家承诺送人上火星的私人企业所面临的问题。

很长一段时间以来，他们一直试图搞清楚宇航员会在太空旅程中经受多少辐射。好奇号登场了，其内部极其便捷地装备了辐射评估探测器（RAD）。该仪器用于收集火星表面的辐射数据。

美国西南研究院的唐·哈斯勒是这项探测的领队。唐·哈斯勒：早在（好奇号）发射的两年前，我们就意识到这个探测器会被安装在航天器内部，这个位置正好就是将来宇航员坐的地方。

于是他们想到：为什么不在太空飞行时就打开仪器呢？发射过后几天，探测器通上电，开始收集数据。研究人员在《科学》杂志上宣称大部分辐射——高达95%的辐射来自银河宇宙射线，而我们根本不知道如何阻隔这类射线。哈斯勒说，只有一种办法可以将这类射线的危害降至最低。

哈斯勒：我想我们只能快点去那里。

以目前的技术水平，前往火星的旅程最短也要六个月。哈斯勒说，宇航员在此期间所受到的辐射量是国际空间站（辐射量）的四倍——后者由于临近地球，辐射受到一定程度的阻隔。

哈斯勒：比如说一个宇航员在空间站呆上六个月，你知道，他所受的（辐射量）大概是80毫西弗，而我们在火星之旅当中会受到330毫西弗的辐射。

而普通的美国人每年所受的辐射量仅为6毫西弗。330毫西弗足以让致癌机率上升将近1.5%。如果从火星往返，这个数字还要乘以二，马上就接近美国辐射保护委员会所建议的辐射上限了。但罗伯特·祖布林并未因此而丧气。

罗伯特·祖布林：辐射并不是拦路虎。

祖布林是火星学会主席以及《赶往火星：红色星球定居计划》的作者。

祖布林：这并不是什么美国食品和药物管理局（FDA）建议所有人都要去做的事情，你知道，我们现在讨论的可是前往火星的任务呢。

祖布林说，火星任务还有很多其他危险，比如“他们真能登陆火星吗”——但很多人愿意承受这样的风险。普通人也有将近20%的癌症死亡率，而一名渴望踏足红色星球的40岁宇航员也许并不在乎给这个概率增加几个百分点。

祖布林：（火星任务）没有延迟的理由，至少就辐射而言不成理由，我们现在就应该开始向火星进军。

科学家对火星本身的辐射问题依然存疑。他们需要更多数据，才能更好地确定火星定居者们的患癌危险性。不过你无需担心，好奇号正为此忙乎着呢。