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Build the space elevator of “The Wandering Earth 2”, a total of several steps – Programmer Sought

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The space elevator in the movie “The Wandering Earth 2”

“ladies and gentlemen,space elevatorabout to reachweightless space station, please get ready and get off from the door on the right. “

“Ladies and gentlemen, we are approaching space station. Please prepare to get off the elevator. The door will be open at the right side.”

If I say, one day you willEarsHearing such announcements,Do you believe?

01.Where did the space elevator come from?

At the beginning of the 20th century, known as the “father of aerospace“Russian scientistsKonstantin TsiolkovskySeveral ideas have been proposed:

useliquidas rocket fuel;

in spacereaction forceis the only way to move;

Connect two or more rockets in series to form a columnmultistage rocketto increase the speed of the rocket.

Today, more than a hundred years later, these ideas have become important applications in the aerospace field.

Konstantin Tsiolkovsky

However, an idea he proposed in 1895,not yet achieved.

This idea is actually very simple:

He proposes building asuper tallThe iron tower was built untilgeosynchronous orbitSo far, erect elevators in the tower, so we canTake the elevator into outer space.

Conceptual drawing of the original space elevator

this isThe prototype of the space elevator.

Does such a tower structure feel familiar?

In fact, this is what Tsiolkovsky was visitingeiffel tower franceInspired from time to time!

This idea is also the closest to our understanding of elevators, but…

Geosynchronous orbit is at a distance of 35786000 meters, currently the tallest building in the world is the Burj Khalifa in Dubai, which is only 828 rice…

Looking at it this way, it seems that the space elevator is dead?

Don’t worry!

At this moment, you are a cosmologist in the middle of the last century, come and think about how to solve this problem!

If you have no idea for a while, try to answer the following question:

New Year’s first question

Click on the blank space to view the answer

If I ask you to put a kite at a height of 250 meters, what else can you do besides running on the ground, continuously putting long strings, and flying the kite into the air?

You can take a helicopter to a higher altitude, throw the kite out, and slowly let the kite reach a height of 250 meters.

Don’t ask me why I fly a kite, and don’t ask me whether the kite line will break, that’s not the point (I don’t admit that this analogy is very loose)!

The point is,Reverse Thinking!

Likewise, we want to build ato outer spaceThe elevator, the most important thing is to provide rope tracks, so, since it is unrealistic to build from the ground up, then we…

can you“throwing” a rope from spacelike throwing a kite?

That is, we can first launch ageosynchronous satelliteand then stretch out the rope from the satellite to “hang” to the ground, and fix it at one end of the ground to form the orbit of the space elevator.

Space elevator concept map (source NASA)

what! Now there is no need to build towers, just ” few ropes “That’s it!

It is this kind of reverse thinking that makes the space elevator less illusory. Today’s space elevator plans are all based on this model.

02、Obayashi Space Elevator Project

Among the many space elevator plans, the space elevator plan announced by the Obayashi group in 2012 is particularly eye-catching.

In February 2012, the famous Japanese construction company Obayashi Group, which is especially good at building tall towers, announced that it would invest in $10 billionConstruction of a space elevator, the estimated speed of the elevator is 200 kilometers per hour, and one-way needs 7 days,plan 2025left and right in the sea near the equatorstart,2050left and right completedoperate.

Dalin group official website concept map

However, the distance from the start of the program has passedten yearsthe prospect seems not to be optimistic. Even Yoji Ishikawa, a senior engineer who has been involved in the research and development of space elevators in Obayashi Group, said frankly: this projectThe more you try, the harder it gets.

First of all, regardless of all external factors, the space elevator is mainly composed of four parts:

elevatorbox bodyrequired for the up and down movement of the box bodycabletrack, offshore for securing cables at the earth’s endbase,as well ascounterweight.

space elevator structure

The first three seem easy enough to understand, but why do you need counterweights?

In the idea of ​​the space elevator just mentioned, we want to “throw” the cable from the geostationary satellite and “hang” all the way to the earth, but as the cable is gradually lowered, the gravitational force it receives will be greater than the centrifugal force, so the cable will touch the geosynchronous satellite. If the inward pulling force is generated, wouldn’t it mean that the cable is left alone, and theThe originally stable geostationary satellite was pulled down?

To solve this problem, we arelower the cableAt the same time, it must also“throw” something up, creating an outward pull that counteracts the inward pull of the cable on the satellite. The thing “thrown” upward must be heavy enough to stabilize the satellite. We call it the counterweight.

However, a new problem came again!

The cable is actually not in a static state, but is rotating at high speed with the geostationary satellite.huge centripetal forcemay exceed the materialTensile limitresulting in the cablebreak yourself off.

Let’s have a deep understanding of how harsh the space elevator’s requirements on the tensile strength of the material are.

In the geocentric reference system, the cable is simplified into a cylinder, the density is ρ, the cross section is S, one end is fixed on the geosynchronous satellite, and the other end is fixed on the equatorial sea base.consider innear geostationary satellite orbitA short section of cable, regardless of various additional loads, the tension it receives can be calculated as follows:

If we use steel as the cable of the space elevator, simplify the deformation of the above formula, and substitute the density value of the steel, we can estimate that the maximum stress that the steel needs to bear must be at least 400 GPa.But in reality, the tensile strength of steel is only 400 MPa!

In other words, even if steel is used as a cable, it will be deformed directly under the strong gravitational force.

So far, we have encounteredVery trickyQuestion: How to find a material with low density but high tensile strength?

03、The cable puzzle of the space elevator

Currently, the most likely to meet the above requirements is thecarbon nanotubes: composed of carbon atomstubular structurenanomaterials, which are currently known theoreticallyHighest mechanical strengthandbest toughnesss material.

carbon nanotube structure

The density of carbon nanotubes is about 1700 kg/㎡. Substituting the above formula into the calculation, it can be obtained that if carbon nanotubes are used as cables for space elevators, the tensile strength of carbon nanotubes must reach at least 90 GPa.

At present, the tensile strength of carbon nanotubes that we have been able to synthesize in experiments can reach 200 GPa; even, for single-walled carbon nanotubes with an ideal structure, the tensile strength can reach 800 GPa.

In this way, we only need to producetens of thousands of kilometers longThe carbon nanotubes are “suspended” from the geostationary satellite and fixed to the sea base station near the equator, and the problem will be solved!

However, our road to explore the space elevator is destined to be bumpy.

In 1991, Japanese scientistsIijima SumioThe discovery and naming of carbon nanotubes injected the freshest blood into the bottlenecked space elevator idea, and many research teams have picked up the space elevator plan again.

However, everyone soon discovered that due to the limitation of the preparation process, the actual length of carbon nanotubes that can be prepared is onlya few millimetersand there are manyStructural defects.

Alas, it seems to have reached a dead end again…

But as the saying goes, thousands of sails pass by the side of the sinking boat, and Wan Muchun is ahead of the sick tree.

In 2013, the team of Professor Wei Fei of Tsinghua University will grow carbon nanotubes per millimeter lengthCatalyst activity probability increased to over 99.5%After that, successfully preparedA single length of more than half a meterand haveperfect structureof carbon nanotubes.

Currently, they are developing lengths inAbove kilometer levelof carbon nanotubes.

It seems that our space ladder has ushered in a glimmer of light!

04.The Practical Dilemma of a Space Elevator

As you may have realized, what has just been discussed isThe simplest physical modelonce you really want to consider the project construction, you need to solve a lot of problemsPractical problems.

For example, in view of the fact that the various high-voltage wires used in life will wear out over time, it is natural for us to ask the following questions:

cables made of carbon nanotubes,Durabilityhow?

After all, the elevator, even if built, is useless if the cables are easily broken.

forExamining the Durability of Carbon Nanotubesin 2015, the Obayashi Group of Japan sent carbon nanotube samples to the400 kilometers above the surfaceIn the nearby Japanese experimental cabin.

Japan’s “Kibo” experimental module

Samples are placed in space 2 yearsThen, they were brought back to Earth again. After analysis, the researchers found that the surface of the carbon nanotubes had been damaged by atomic oxygen.

It should be known that the altitude of 400 kilometers belongs to the thermosphere in the atmosphere, and the air has alreadyextremely thinand even so, 2 years have already destroyed the carbon nanotubes.

It is conceivable that the cables directly exposed in the lowest troposphere will facemore severetest.

In addition to being destroyed by oxygen in the atomic state, it also needs to face all kinds of possible wind, sun and rain, and may even encounter various extreme weather such as lightning and hurricanes…

Increased cable durabilityThe research in this field is obviously difficult, but as long as the road is not blocked, we will not stop the pace of exploration.

Of course, in addition to durability issues, there area lot of problemswaiting for us to solve…

For example, how to ensure that the elevator car has enough power support to go all the way from the ground to the space station?

If it rises halfway, the space elevatorPowertrain Sudden Failureis simply the scene of a high-altitude survival thriller, and I shudder to think about it.

If the elevator stopped at this moment…
(Source: Wandering Earth 2 Trailer)

As another example, how to make a space elevatorauto dodgeSpace debris and some satellites that might collide?

Once the evasion is not timely, the consequences will be unimaginable.

It can be said that the sentence is verified:

The space elevator, the more you try, the more difficult it becomes.

05、Why We Are Obsessed With Space Elevators

At this point, you are likely to ask, since it is so difficult to build a space elevator, why do we continue topersistenthereSeemingly impossibleWhat about the idea?

Because we yearn for the stars and the sea.

Cough cough cough, don’t talk about these, let’s talk about reality:

In current international commercial satellite launches, the transportation cost per kilogram of payload is between $2,000-20,000between.Suppose the editor wants to travel to space, at least 100,000.

Assuming that the space elevator can be successfully constructed, regardless of the initial construction cost, according to the estimation of the Obayashi Group in Japan, the transportation cost per kilogram of load is about $200!

In other words, I only need to spend Around RMB 70,000you can go to space travel!

After the space elevator is built, in addition to making space tourism within reach, we can alsolow costTransportation of materials on Earth and in space.

This may become the most important event in the history of human space exploration.Excitingturning point!

06、lifetime

Now, please look up to the sky and imagine.

Every second that seems dull is witnessing the birth of history.

In your lifetime, you will see agrand ladderpiercing the distant clouds toDestroyedmomentum, constantly rushed to the surface, and finallyAcross the worldAbsolutely gorgeous past and present.

Source: Wandering Earth 2 Trailer

Thinking of this, I really burst into tears.

This article comes from the WeChat public account:Institute of Physics, Chinese Academy of Sciences (ID: cas-iop)Author: Mueller Family Nanny

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