Wandering Earth: Rocket scientists explain how we move our planet.
This situation may come true one day. In five billion years, the sun will run out of fuel and expand, which is likely to engulf the earth. The more immediate threat is the disaster of global warming. Moving the earth to a wider orbit may be a solution-theoretically possible.
But how can we solve this problem? What are the engineering challenges? For demonstration, let's assume that our goal is to move the earth from its current orbit to an orbit 50% away from the sun, similar to Mars.
For many years, we have been designing technology to remove small celestial bodies-asteroids-from orbit, mainly to protect the earth from impact. Some are based on impulsive, usually destructive actions: nuclear explosions near or on the surface of asteroids, or "kinetic energy colliders", such as spacecraft hitting asteroids at high speed. Because they are destructive, these obviously do not apply to the earth.
Other technologies include very gentle and sustained long-term propulsion, provided by tugboats docked on the surface of asteroids or spacecraft hovering near them (pushing gravity or other methods). But this is impossible for the earth, because its mass is huge compared with the largest asteroid.
In fact, we have removed the earth from orbit. Every time the probe leaves the earth and enters another planet, it will produce a small impact on the earth in the opposite direction, similar to the recoil of a gun. Fortunately for us-but unfortunately, in order to move the earth-this effect is very small.
Space Exploration Technologies' Falcon Heavy is the most powerful launch vehicle today. In order to change the orbit of Mars, we need to launch 30 billion times at full capacity. All these rockets will be made of materials equivalent to 85% of the earth, and only 15% of the earth remains in the orbit of Mars.
Electric propeller is a more effective method to accelerate mass, especially ion driver, which pushes the container forward by emitting a stream of driven particles. We can point to the tail of the earth's orbit and launch electric thrusters.
The super-large propeller should be at an altitude of 1000 km, beyond the earth's atmosphere, but it is still firmly attached to the earth with rigid beams to transmit thrust. If the ion beam is emitted in the right direction at a speed of 40 kilometers per second, we still need to spray the rest of the ion equivalent to the earth's mass 13% to move the remaining 87%.
Because light has momentum, but no mass, we can also continuously supply power to focused beams (such as lasers). The required energy will be collected from the sun without consuming the mass of the earth. Even with the huge 100GW laser equipment that breaks through the idea in the Starshot project, which aims to promote the space system to detect nearby stars, it still needs to be used continuously for 300 million years to realize the orbital change.
But the solar sail is stationed next to the earth, and light can also be directly reflected from the sun to the earth. Researchers have proved that to achieve orbit transfer in the time scale of10 billion years, a reflector that is 19 times larger than the diameter of the earth is needed.
A well-known technique for two orbiting objects to exchange momentum and change speed is through a closed channel or gravity slingshot. This maneuver has been widely used by interstellar probes. For example, during the period from 20 14 to 20 16, the Rosetta spacecraft that visited comet 67P during its ten-year journey passed near the earth twice in 2005 and 2007.
Therefore, the earth's gravity field has brought Rosetta considerable acceleration, which can only be realized by propeller. Therefore, the earth gets the opposite and the same impulse-although it has no measurable influence due to the mass of the earth.
But what if we can use something bigger than a spaceship to execute a slingshot? Asteroids can of course be redirected by the earth. Although the interaction in the earth's orbit is very small, this action can be repeated many times, and eventually a considerable change in the earth's orbit will be realized.
Some areas of the solar system are densely populated with small objects, such as asteroids and comets. Many of them are small enough to be moved by real technology, but they are still several orders of magnitude larger than the gases actually emitted by the earth.
Through accurate trajectory design, we can use the so-called "Δ V lever"-a small celestial body can swing through the earth far away from its orbit, thus providing greater momentum for our planet. It seems very exciting, but it is estimated that we need one million such asteroid close-range passages, each with an interval of thousands of years, to keep up with the expansion of the sun.
Of all the available options, using multiple asteroid slingshots seems to be the easiest to achieve at present. But in the future, if we learn how to build huge space structures or super-large laser arrays, then developing light may be the key. These can also be used for space exploration.
Although this is feasible in theory and may be technically feasible one day, in fact, it may be easier to move our species to our planet's next-door neighbor, Mars, which may survive the destruction of the sun. After all, we have landed and drifted on its surface several times.
Considering how challenging it is to move the earth, it may not sound difficult to settle on Mars, make it livable and move the population of the earth over time.