Liquid hydrogen and liquid oxygen engines powered the Space Age, but they can only get us so far.

液態氫氣和液態氧氣引擎驅動了太空時代，但它們也只能帶我們到這裡了。

If we want to travel to deep space and beyond without waiting for the planets to align,

如果我們不想等到行星對準才能進入深層太空的話，

we're going to have to come up with some new propulsion systems.

我們便須ul4想出一些新的推進系統。

The problem with chemical rockets is the fuel is heavy, and for all that weight, it's not very efficient.

燃料很重是化學燃料火箭的問題，以燃料的佔整體的比例來說，這很沒有效率。

The fuel's energy is limited to what's stored in the chemical bonds,

燃料的能量僅限於化學鍵中儲存的能量，

and after 90 years of research, chemical rockets aren't going to get much better.

經過了 90 年的研究之後，化學燃料火箭並沒有取得太多的進展。

Plus, once that candle's lit, it uses all its fuel in one burst

再加上，一旦點火器點燃，他就會一次用完所有的燃料

and then coasts the rest of the way to the destination.

然後沿著路線一路飛到目的地。

If the kids are yelling in the back, you can't turn this rocket around, you know what I'm saying?

假如孩子們吵著要回去，你也無法將火箭轉向，你懂我在說什麼嗎?

Well, you could orient it that way with hydrazine engines like the ones satellites use,

你也許可以向人造衛星一樣運用聯氨引擎來導向，

but those don't actually have enough thrust to do much more than orientation.

但那其實沒有足夠的推力來做導向以外的事情。

Whatever way the chemical rocket was pointing, that's where you're going.

無論化學燃料引擎指向什麼方向，那便是你將前往的方向。

So to explore deep space, NASA is looking past the energy stored in chemical bonds.

因此，為了要探索深空，NASA 正在尋找化學鍵中儲存的能量。

Another propulsion technology that's been around since the 60s is just showing promise in the last 20 years: ion engines.

另一項出現於 60 年代左右而在過去 20 年間開始嶄露頭角的推進技術 : 離子引擎。

Ion engines work by accelerating charged atoms, like xenon ion, through a magnetic field, and out the back of the spacecraft.

離子引擎藉由加速帶電原子，例如氙離子，經過一個磁場再由太空船的背面釋出。

The fuel is lightweight and provides a low amount of thrust over a very long period of time,

燃料非常輕巧，而且在非常長的時間中提供提供了小量的推進，

so in theory, they're great for long-term deep-space exploration.

因此理論上來說，它們對於長程深空探索來說是非常棒的。

Early engines, though, destroyed themselves as the ions eroded the walls and it's hard to have a long-term mission with a short-term engine.

早期的引擎，會因為引擎壁遭到離子的侵蝕而損毀而且依靠短程引擎難以承擔長程任務。

Engineers have finally cracked the puzzle by diverting the magnetic field around the walls, to stop the ions from bombarding it, and recent missions

工程師最終解決了難題，藉由使靠近引擎壁的磁場發散來防止離子的轟擊，而最近的任務

like the Dawn Space Probe, sent to the asteroid Ceres, used ion engines to power it once it was out of Earth's orbit.

像是送往 Cere 小行星的曙光號探測器，在離開地球軌道後便使用離子引擎來驅動。

Another novel idea is getting rid of onboard fuel altogether, and letting the Sun push the craft along.

另一個新穎的想法是完全擺脫火箭載運的燃料，並藉由太陽來推動太空船。

That's the principle harnessed by solar sails, and they're exactly what they sound like:

那就是太陽帆的原理，而這正如你所聽到的一樣 :

they're sails as large as a football field, and 40-100x thinner than a sheet of paper.

它們是與足球場一樣大的帆，但卻只有一張紙的 40 至 100 倍薄。

When fully unfurled, they catch the sun's light, and away they go.

當它完全展開，他們能夠捕捉住太陽光，然後便開始飛離。

Despite photons having no rest mass, they do have energy, which means they do carry a tiny amount of momentum.

儘管光子不具有靜止質量，但他們具有能量，這意味著他們能承載微小的動量。

When they bounce off the craft's surface, they impart their momentum.

當他們在太陽帆的表面反彈時，他們便傳遞出動量。

So, an enormous sail out in space can take advantage of the practically endless stream of photons from the Sun,

因此，在太空中的太陽帆能夠利用理論上來說取之不盡的太陽光子流，

accelerating for as long enough light keeps hitting it.

只要有足夠的光不斷衝擊太陽帆，便能一直加速。

The Japanese space agency JAXA launched the first solar sail IKAROS in 2010,

日本的太空機構 JAXA 在 2010 年時發射了第一個太陽帆 IKAROS ，

and one month after it unfurled, JAXA reported the craft was accelerating due to photonic pressure.

在它展開的一個月後，JAXA 回報這個太空船正因光子壓力而加速。

(Just don't go too close to the Sun, IKAROS.)

(不要靠太陽太近啊，IKAROS) (伊卡洛斯，希臘神話中代達羅斯的兒子，因為飛得太過靠近太陽導致蠟翼融化墜海而死)

Solar sails work well when they're close enough to the Sun,

太陽帆在足夠靠近太陽時能良好運行，

but out past Mars, the power of the Sun fades, making solar sails impractical past that point.

但當飛越火星後，太陽能逐漸減弱，使太陽帆沒有辦法通過那一點。

If you can't wait for an ion engine or solar sail to pick up speed, there is the nuclear option...

如果你等不及離子引擎或太陽帆啟航，這裡有個核能選項...從字面上來看。

literally. Some scientists have proposed using fusion or efficient propulsion systems to get humans to Mars in one month instead of seven.

某些科學家提議運用核融合或高效能推進系統在一個月內把人類帶到火星上，而非七個月。

Proposals vary, with some using nuclear reactors to generate plasma

提議各不相同，有些提議用核反應爐來產生電漿

that's then accelerated with a magnetic field -- like an ion engine on steroids.

然後再經由磁場來加速 -- 就像是類固醇上的離子引擎。

Others would use hydrogen atoms that are forced together by collapsing lithium rings around them to generate pulses of fusion.

其他想法有運用藉由使鋰環在被強壓在一起的氫原子周圍塌縮來產生核融合脈衝。

This method could provide the same amount of energy as four litres of rocket propellant with an amount of fuel as big as a grain of sand.

這個方法能夠以一顆砂粒大小的燃料提供與四公升火箭推進劑等量的能量。

But these ideas have a lot of hurdles, and are still a long way off.

但要實現這些想法有許多的障礙，而還有一段很長的路要走。

Then again, so are other planets,

其他的星球亦然，

and if we're going to send humans to any of them,

如果我們想要將人類送往這些星球，

we prefer the journey be as fast as possible.

我們會希望旅程越短越好。

We'll still need chemical rockets to get us out of Earth's orbit.

我們仍然需要化學燃料火箭來讓我們離開地球軌道。

But once we develop these technologies, who knows where we go from there?

然而一旦我們發展出這些技術，誰知道我們將會從地球軌道飛向什麼地方呢？

Hey! While you're here, check out this next video at NASA's Jet Propulsion Laboratory

嘿! 趁你還在這裡時，看看下一部在 NASA 的推進實驗室拍攝的影片

which shows how the design and manufacturing of future deep space exploration is sometimes based on origami.

這部影片顯示了未來深空探索的設計與製造有時是奠基於摺紙技術上的。

Don't forget to subscribe for awesome science videos every week, and thanks for watching.

別忘了訂閱每個星期都有的優質科學影片喔，謝謝觀看。