Could We Move the Entire Planet Earth to a New Orbit?

我們能把整個地球移到一個新的軌道上嗎？

In the Chinese science fiction film The Wandering Earth， recently released on Netflix， humanity attempts to change the Earth‘s orbit using enormous thrusters in order to escape the expanding sun — and prevent a collision with Jupiter。

在中國科幻電影《流浪的地球》中，人類試圖利用巨大的推進器改變地球的軌道，以逃離不斷膨脹的太陽，並防止與木星相撞。

The scenario may one day come true。 In five billion years， the sun will run out of fuel and expand， most likely engulfing the Earth。 A more immediate threat is a global warming apocalypse。 Moving the Earth to a wider orbit could be a solution — and it is possible in theory。

這種情況有一天可能會成為現實。50億年後，太陽將耗盡燃料並膨脹，很可能吞噬地球。更直接的威脅是全球變暖的大災難。把地球移到更寬的軌道上可能是一個解決方案，而且在理論上是可能的。

But how could we go about it and what are the engineering challenges？ For the sake of argument， let us assume that we aim to move the Earth from its current orbit to an orbit 50% further from the sun， similar to Mars’。

但是我們該怎麼做呢工程上有什麼挑戰呢？為了便於討論，讓我們假設我們的目標是把地球從目前的軌道移到離太陽50%遠的軌道，類似於火星的軌道。

We have been devising techniques to move small bodies — asteroids — from their orbit for many years， mainly to protect our planet from impacts。 Some are based on an impulsive， and often destructive， action： a nuclear blast near or on the surface of the asteroid， or a “kineticimpactor”， for example a spacecraft colliding with the asteroid at high velocity。 These are clearly not applicable to Earth due to their destructive nature。

多年來，我們一直在設計將小行星等小天體移出軌道的技術，主要是為了保護地球免受撞擊。有些是基於一種衝動性的、往往是破壞性的作用：小行星附近或表面的核爆炸，或“動力衝擊器”，例如航天器與小行星高速相撞。由於它們的破壞性，它們顯然不適用於地球。

Other techniques instead involve a very gentle， continuous push over a long time， provided by a tugboat docked on the surface of the asteroid， or a spacecraft hovering near it （pushing through gravity or other methods）。 But this would be impossible for the Earth as its mass is enormous compared to even the largest asteroids。

相反，其他的技術包括一個非常溫和的，在很長一段時間內持續推動，由停靠在小行星表面的拖船提供，或由一個航天器在它附近盤旋（透過重力或其他方法推動）。但這對地球來說是不可能的，因為地球的質量甚至比最大的小行星還要大。

Electric thrusters

電動推進器

We have actually already been moving the Earth from its orbit。 Every time a probe leaves the Earth for another planet， it imparts a small impulse to the Earth in the opposite direction， similar to the recoil of a gun。 Luckily for us — but unfortunately for the purpose of moving the Earth — this effect is incredibly small。

我們實際上已經把地球從軌道上移開了。每次探測器離開地球前往另一顆行星時，都會向地球施加一個相反方向的小脈衝，類似於槍的反衝。對我們來說幸運的是——但不幸的是為了移動地球——這種影響非常小。

SpaceX‘s Falcon Heavy is the most capable launch vehicle today。 We would need 300 billion billion launches at full capacity in order to achieve the orbit change to Mars。 The material making up all these rockets would be equivalent to 85% of the Earth， leaving only 15% of Earth in Mars orbit。

SpaceX的獵鷹重型火箭是目前最有能力的運載火箭。我們將需要3000億次發射滿負荷才能實現火星軌道的改變。構成所有這些火箭的材料將相當於地球的85%，只剩下地球的15%在火星軌道上。

An electric thruster is a much more efficient way to accelerate mass — in particular ion drives， which work by firing out a stream of charged particles that propel the vessel forward。 We could point and fire an electric thruster in the trailing direction of Earth’s orbit。

電推力器是一種更有效的加速質量的方法——尤其是離子驅動，它的工作原理是釋放出一股帶電粒子流，推動飛船前進。我們可以指向地球軌道的尾部發射一個電子推進器。

The oversized thruster should be 1，000 kilometres above sea level， beyond Earth‘s atmosphere， but still solidly attached to the Earth with a rigid beam， to transmit the pushing force。 With an ion beam fired at 40 kilometres per second in the right direction， we would still need to eject the equivalent of 13% of the mass of the Earth in ions to move the remaining 87%。

超大型推進器應該在海平面以上1000公里處，在地球大氣層之外，但仍然用一根剛性梁牢牢地與地球相連，以傳遞推力。如果一束離子束以每秒40公里的速度向正確的方向發射，我們仍然需要噴射相當於地球質量13%的離子來移動剩下的87%。

Sailing on light

航行在光

As light carries momentum， but no mass， we may also be able to continuously power a focused light beam， such as a laser。 The required power would be collected from the sun， and no Earth mass would be consumed。 Even using the enormous 100GW laser plant envisaged by the Breakthrough Starshot project， which aims to propel spacecraft out of the solar system to explore neighbouring stars， it would still take three billion billion years of continuous use to achieve the orbital change。

由於光攜帶動量，但沒有質量，我們也可以連續地為聚焦的光束提供動力，比如鐳射。所需的能量將從太陽收集，而不會消耗地球的質量。即使使用“突破攝星計劃”（Breakthrough Starshot project）設想的巨大的100GW鐳射工廠，也需要30億年的持續使用才能實現軌道的改變。“突破攝星計劃”的目標是推動宇宙飛船飛出太陽系，探索鄰近的恆星。

But light can also be reflected directly from the sun to the Earth using a solar sailstationed next to the Earth。 Researchers have shown that it would need a reflective disc 19 times bigger than the Earth’s diameter to achieve the orbital change over a timescale of one billion years。

但是光也可以透過安裝在地球附近的太陽帆直接從太陽反射到地球。研究人員表示，它需要一個比地球直徑大19倍的反射盤，才能在10億年的時間尺度內實現軌道變化。

Interplanetary billiard

星際檯球

A well-known technique for two orbiting bodies to exchange momentum and change their velocity is with a close passage， or gravitational slingshot。 This type of manoeuvre has been extensively used by interplanetary probes。 For example， the Rosetta spacecraft that visited comet 67P in 2014-2016， during its ten-year journey to the comet passed in the vicinity of the Earth twice， in 2005 and 2007。

兩顆軌道物體交換動量和改變速度的著名技術是透過近距離通道，或引力彈弓。這種操縱方式已被星際探測器廣泛使用。例如，在2014-2016年訪問67P彗星的羅塞塔號飛船，在其10年的彗星之旅中，在2005年和2007年兩次經過地球附近。

As a result， the gravity field of the Earth imparted a substantial acceleration to Rosetta， which would have been unachievable solely using thrusters。 Consequently， the Earth received an opposite and equal impulse — although this did not have any measurable effect due to Earth‘s mass。

結果，地球的重力場給羅塞塔帶來了巨大的加速度，而這僅靠推進器是無法實現的。結果，地球受到了一個相反的、相等的衝量——儘管由於地球的質量，這個衝量沒有任何可測量的影響。

But what if we could perform a slingshot， using something much more massive than a spacecraft？ Asteroids can certainly be redirected by the Earth， and while the mutual effect on Earth’s orbit will be tiny， this action can be repeated numerous times to ultimately achieve a considerable Earth orbit change。

但如果我們能用比宇宙飛船大得多的東西來彈弓呢？小行星當然可以被地球重定向，雖然對地球軌道的相互影響很小，但這種作用可以重複無數次，最終實現可觀的地球軌道變化。

Some regions of the solar system are dense with small bodies such as asteroids and comets， the mass of many of which is small enough to be moved with realistic technology， but still orders of magnitude larger than what can be realistically launched from Earth。

太陽系的一些區域密集著小行星和彗星等小天體，其中許多小天體的質量小到可以用現實的技術移動，但仍然比從地球上實際發射的物體要大幾個數量級。

With accurate trajectory design， it is possible to exploit so-called “Δv leveraging” — a small body can be nudged out of its orbit and as a result swing past the Earth， providing a much larger impulse to our planet。 This may seem exciting， but it has been estimated that we would need a million such asteroid close passes， each spaced about a few thousand years apart， to keep up with the sun‘s expansion。

精確的軌跡設計，可以利用所謂的“Δv利用”——一個小身體可以推動它的軌道，因此搖擺過去的地球，為我們的星球提供更大的衝動。這似乎令人興奮，但據估計，我們需要100萬顆這樣的小行星近距離掠過地球，每顆相隔幾千年，才能跟上太陽的膨脹速度。

The verdict

判決結果

Of all the options available， using multiple asteroid slingshots seems the most achievable right now。 But in the future， exploiting light might be the key — if we learn how to build giant space structures or super-powerful laser arrays。 These could also be used for space exploration。

在所有可用的選項中，使用多個小行星彈弓似乎是目前最可行的。但在未來，如果我們學會如何建造巨大的空間結構或超強的鐳射陣列，利用光可能是關鍵。這些也可以用於太空探索。

But while it is theoretically possible， and may one day be technically feasible， it might actually be easier to move our species to our planetary next-door neighbour， Mars， which may survive the sun’s destruction。 We have， after all， already landed on and roved its surface several times。

雖然理論上是可能的，也許有一天在技術上是可行的，但實際上可能更容易把我們的物種遷移到我們的行星鄰居火星，那裡可能在太陽毀滅後倖存下來。畢竟，我們已經在火星表面著陸並繞其表面旋轉了好幾次。

After considering how challenging it would be to move the Earth， colonising Mars， making it habitable and moving Earth‘s population there over time， might not sound as difficult after all。

考慮到移動地球是多麼具有挑戰性之後，殖民火星，使其適宜居住，並隨著時間的推移將地球人口遷移到那裡，聽起來可能根本不那麼困難。

Matteo Ceriotti， Lecturer in space systems engineering， University of Glasgow

格拉斯哥大學空間系統工程講師Matteo Ceriotti演講

This article is republished from The Conversation under a Creative Commons license。 Read the original article。

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