In "Future Technology Experience Center Season 1", I once gave you a program titled "How far is space tourism from us?" In that program, I made a prediction:

But in my opinion, this kind of space tourism does not actually leave the earth. We are still moving within the gravitational range of the earth.

This time I want to push this topic forward. I really want to talk to you: In the foreseeable future, is it possible for humans to really leave the earth and go to the moon or Mars for a vacation? ? Or further afield, can ordinary people use the moon or a space station as a base to take a trip to more distant Jupiter, Saturn, or even Pluto? In the field of aerospace, is there any key technological singularity? Once this singularity is exceeded, we will usher in a big explosion in the aerospace industry?

The most difficult thing in the aerospace industry is to escape the gravity of the earth. We can imagine the earth as a gravity well, and we humans are the frogs at the bottom of the well. As long as we can jump out of this well, there will be a vast plain outside, and the vast universe will be full of possibilities. soar. Why is it said that jumping out of this well will lead to smooth sailing? Because sailing in space is actually very energy-saving, because there is almost no resistance in a vacuum, space ships need to consume fuel when accelerating, decelerating, and changing orbits. Compared with the fuel consumed to overcome the gravity of the earth, it is simply The little witch saw the big witch.

The only technology that humans have for jumping out of gravity wells is rocket technology, but the biggest problem with rockets is that the cost of launch is too high. One of the biggest reasons is that in the past, rockets were disposable consumables, and it cost tens to hundreds of millions of dollars to build a rocket. For example, rocket launch is like a rich man buying a Boeing 737 passenger plane, flying it once and then throwing it away. The next time it flies, he will buy another one. How many rich people like this are there in the world?

Therefore, in order to reduce the cost of rocket launches, whether it is Elon Musk’s Space Exploration Company, Virgin Galactic, or Blue Origin, what they are doing is trying to make the rocket Can be recycled and reused.

In early 2020, SpaceX’s director of vehicle integration, Christopher Couluris, said at a briefing that the single launch cost of a recyclable Falcon 9 could eventually be reduced to $28 million. [1]. What is this concept? The maximum payload of a recyclable Falcon 9 is about 30 tons, which is about $930,000 per ton, which is almost 200 times the price of ordinary air transportation today. You may not realize how big the 200-fold difference is. For example, it’s like the difference between you with a monthly salary of 10,000 yuan and your boss with a monthly salary of 2 million yuan.

Virgin Galactic, another space tourism company, has even begun selling space tourism tickets. According to U.S. Securities and Exchange Commission (SEC) documents[2]: Virgin Galactic plans to send a group of tourists into space every 32 hours by 2023. Although this so-called "space tourism" is actually just like sitting in a cannonball, just taking a brief look at an altitude of 100 kilometers above the earth's surface, and then quickly falling back to the earth's surface, the ticket price is as high as 250,000 US dollars per ticket. Virgin Galactic founder Richard Branson’s most optimistic estimate is that in 10 years, the ticket price can be reduced to less than 50,000 US dollars. Another company called Blue Origin has also announced the price of space tourism. almost.

Hearing this, I estimate that many people will compare space flight with the traditional transportation industry, and may think: large-scale production will inevitably bring about rapid cost reduction, as long as the space tourism market can With continued cultivation, ticket prices should become lower and lower until all ordinary people can afford them. Just like cars, ships, and civil aviation in the past, didn't they all go through a process from the rich to the common people?

The problem is - space launch is really not as simple as thought.

In order to explain its difficulties to you clearly, I am going to tell you about some high-end goods today.

There is a famous rocket equation, and its proposer is the Russian scientist Konstantin Eduardovich Tsiolkovsky, who is known as the "father of human rockets". This rocket equation is like a safety circle drawn by Sun Wukong for Tang Monk. No matter how much human rockets improve their technology, they cannot escape the price-performance ratio circled by it.

Before explaining this equation, let’s first take a look at the essential differences between rockets as a means of transportation and cars, ships, and airplanes.

First of all, only rockets need to constantly fight against gravity during movement, while other transportation vehicles basically do not need to fight against gravity during movement. In more popular terms: rockets move vertically upward relative to the ground, while other transportation vehicles basically maintain horizontal motion. Don't underestimate the essential difference caused by the different directions of movement. Let me explain it to you:

The resistance that the car has to overcome during movement is mainly the friction from the ground. The size of the friction is mainly Depends on the rolling friction coefficient between the tire and the ground and has very little to do with the weight of the car itself. For example, on ordinary city roads, the rolling friction coefficient is about 0.02, which means that when the weight of the car doubles, the friction force only increases by about 0.02 times. Therefore, in terms of cost performance, the greater the truck load, the lower the energy consumption per unit weight.

The resistance that a ship has to overcome during its movement mainly comes from the resistance of water to the ship. The size of the water resistance mainly depends on the speed of the ship and the contact area between the ship and the water. It has nothing to do with the mass of the ship itself. big. The calculation formula is more complicated, but the conclusion is similar to that of a car. The larger the load capacity of the ship, the lower the energy consumption per unit weight. Therefore, each ocean-going ship is bigger than the other. If it were not restricted by the locks in several major straits in the world, we would make the transport ships even bigger.

The resistance that an airplane must overcome during its movement mainly comes from air resistance. The magnitude of air resistance is very similar to the resistance encountered by a ship in the water. The conclusion is also similar: the greater the passenger capacity of an airplane, the greater its unit weight. The lower the energy consumption.

Therefore, the cost-effectiveness of transportation vehicles such as cars, ships, and airplanes can be summarized in one sentence: the bigger, the more cost-effective.

However, this rule will be broken when the Rockets come here. Because the rocket needs to move upward against the force of gravity, the greatest resistance the rocket encounters is gravity, and the magnitude of gravity is almost only related to one thing, and that is the mass of the rocket. The greater the mass of the rocket, the greater the resistance that needs to be overcome. But the very paradox is that the fuel that powers the rocket itself has a huge mass. The more fuel is added, the more fuel needs to be consumed to send the fuel to the sky. This is a bit like the logistics team that delivered grain and grass during ancient marches and wars. The more people and animals in the team, the more grain and grass they had to eat. This complicates calculating the relationship between a rocket's fuel load and its payload.

The first person to be recognized for clarifying this complex relationship was Tsiolkovsky. The rocket equation he proposed is also called Tsiolkovsky rocket. equation. To deeply understand the current dilemma faced by human aerospace technology, we must first deeply understand the rocket equation.

I would like to ask everyone not to be afraid, this equation is not difficult to understand. In the next few minutes, although it is a bit high-energy, as long as you concentrate, you will be able to understand it. Once you understand it, you will have great fun in understanding the principles.

This equation approximately describes the relationship between the initial total mass of the rocket at takeoff, m0, and the pure mass of the rocket, m1, that remains after the fuel is burned.

The relationship between them is a linear function relationship. If it is written using an equation, it is:

m1 = am0

If we change m1 to the familiar y, m0 is changed to Everyone is familiar with x, so it is written like this:

y = ax

What does the image of this linear function look like in the rectangular coordinate system? It's very simple, it's just a straight line passing through the origin. If the coefficient a=1, then it is a straight line with a slope of 45 degrees.

The slope of this line depends on the value of the coefficient a.

If a1, the slope is greater than 45 degrees.

This 45-degree slope is like a watershed. If the slope is exactly 45 degrees, it means: if x doubles, then y will also double exactly. Between the two, The same proportion increases or decreases. But if the slope is greater than 45 degrees, that is, if a is greater than 1, then x will double and y will more than double. Conversely, if the slope is less than 45 degrees, then doubling x will less than double y.

We have set before that y is equivalent to the pure mass remaining after the rocket fuel is burned out, and x is equivalent to the initial total mass of the rocket. In other words, whether the value of the slope a is greater than 1 or less than 1 A key question is decided, that is, if the initial mass of the rocket is doubled, after the rocket burns out the fuel, can the remaining pure mass be more than doubled or less than doubled. In layman's terms, whether it is more cost-effective to build a bigger rocket or less cost-effective to build a larger rocket depends on whether the value of the fatal coefficient a is less than 1 or greater than 1.

The greatest contribution of Tsiolkovsky, the father of rockets, was to clarify the calculation method of this coefficient a. He found that the value of a basically depends on two key parameters:

So, what is the specific mathematical relationship between the coefficient a and these two parameters?

Because our purpose is to study the approximate value of a, whether it is greater than 1 or less than 1, therefore, below I will explain and calculate this formula for you, while analyzing the selection of this formula. Value range.

To calculate the value range of a, we need to divide it into the following three steps:

Okay, the calculation is over. Through these three steps, we have calculated the coefficient a value. Because the previous values ??have gone through a series of simplifications, the actual value of a is approximately around 0.05.

Therefore, the relationship between the initial total mass m0 of the rocket when it takes off and the pure mass m1 of the rocket after acceleration can be approximately written as:

m1 = 0.05m0

What is this concept? Let me interpret it for you. This roughly means: if the fuel weight of the rocket is doubled, the payload of the rocket can only be increased by 0.05 times; if you want to double the payload, the rocket must add 20 times more fuel.

Does this conclusion surprise you? This is the biggest embarrassment and dilemma faced by mankind's rocket-based aerospace technology at present. We have to work 20 times hard to get 1 times the return. You have to know that you can’t just add 20 times the fuel by 20 times. More fuel means that the cavity containing the fuel must be made larger and heavier. The requirements for cavity materials, engineering manufacturing technology, and control technology are all increased proportionally, which in turn will cause the rocket to become heavier. , requiring more fuel, a bit like a vicious cycle.

In human history, the rocket with the strongest carrying capacity so far is the Saturn V rocket that sent the Apollo moon landing spacecraft into the sky. Its dead weight reached an astonishing 3,000 tons, but it could only Send 140 tons of stuff to low Earth orbit. This is the fundamental reason why space launches are so expensive, because the effective utilization rate of rocket fuel is too low.

Having said this, we can draw a conclusion: As long as our space launches still use rocket technology, unfortunately, in the foreseeable future, it may not be possible for ordinary people to realize space tourism. dream. Space tourism will always be entertainment for the rich. By the same token, because costs cannot be reduced, large-scale construction of space stations is also wishful thinking. It is too expensive to send things on the ground into space.

To truly reduce costs, we must find another way to completely get rid of the constraints of the Tsiolkovsky rocket equation on human aerospace industry. The so-called getting rid of the confinement of the rocket equation is to separate the energy and the load - the fuel (or the material that provides energy) does not need to go up to the sky with the load.

Based on the scientific theories currently available to mankind, there is only one way.

The essential difference between an elevator and a rocket is that the energy provider and load are completely separated. The elevator can rely on electricity without any mass to rise. It is not governed by the rocket equation at all. Its energy consumption is the same as that of a skyscraper. The energy consumption of the elevator is the same.

The earliest proposer of the idea of ??a space elevator is Tsiolkovsky, the father of rockets whom we have mentioned repeatedly before. As early as 1895, he formally proposed the basic principles of a space elevator.

In the simplest terms, the principle of a space elevator is to hang a long rope from a geostationary satellite until it reaches the ground. Because geostationary satellites are synchronous with the Earth's rotation, the point where the rope contacts the ground can theoretically be fixed somewhere on the Earth's equator. If an elevator that can lift is installed on this rope, it can slowly rise into space.

Of course, this is definitely an oversimplification, and the actual situation is more complicated than this. The height of the geosynchronous orbit is about 36,000 kilometers above the Earth's equator, so the mass of a 36,000-kilometer-long rope will also be quite large. Then the rope plus the center of mass of the geosynchronous satellite is below the height of the geosynchronous orbit. , so there is no guarantee that they will be synchronized with the earth's rotation as a whole.

To solve this problem, we need to continue to lengthen the rope, extend it all the way to the top of the satellite, and then connect it to a huge counterweight object, so that the final homogeneous center of all connected objects is exactly the same. Landed in geosynchronous orbit. If you still don’t quite understand it until here, you can take a look at the schematic diagram I attached, which can help you quickly understand the principle and structure of the space elevator.

Scientists imagine that a near-Earth asteroid can be captured from space to act as a balancing weight in this structure, or that various scrapped satellites left by humans in space can be collected. In short, there are no fundamental technical difficulties here. Even if you just use rockets to keep sending things upward, it is still a one-time investment, and it is worth it no matter how expensive it is. If you search with the keyword "Space elevator" on the famous paper search website Science Direct, you can find more than 30 papers with this keyword in the title. Space elevators are not only a favorite subject of science fiction novels, but also a serious topic that scientists have been discussing.

The real difficulty in building a space elevator is the cable that is more than 40,000 kilometers long. What materials should we use to make this cable?

Our material requirements for this cable are: its mass must be very, very light, and its tensile strength must be very, very high.

In materials science, the unit of material strength is "Uri", which is the ratio of the ultimate force that a unit area can withstand and the density of the material. The strength of titanium alloy, which is often used to make spectacle legs, is about 300,000 yuri, and the strength of Kevlar, a super-strong material invented by DuPont in the United States, is about 2.5 million yuri. To be a cable for a space elevator, it is calculated that its strength should be between 30 million and 80 million Yuri.

What material can achieve such high strength?

In fact, humans have already found this material.

We have already mentioned it in the previous program about new materials. It is just rolling graphene into a cylinder shape. This is - carbon nanotubes. Microscopically, it is carbon atoms arranged in the shape of a straw, with a diameter smaller than that of a human hair. However, the strength of the material decreases as the thickness of the carbon atoms increases. To obtain the highest strength, it is necessary to create carbon nanotubes formed by a single layer of carbon atoms. If the craftsmanship is perfect, a single layer of carbon nanotubes could theoretically be as strong as 50 million to 60 million Yuri, which would be enough to be used as a cable for a space elevator.

There are also materials on the market called carbon nanotubes, but those cannot actually be called real carbon nanotubes because the carbon atoms are not thin enough.

In 2013, Professor Wei Fei’s team at Tsinghua University in my country successfully produced the longest carbon nanotube in the world at that time, with a length of about 0.55 meters. This achievement was published online in a famous international materials science journal. "American Chemical Nano" [3]. Six years later, in 2019, Professor Wei Fei's team increased this world record by 10 centimeters and created a 0.65-meter-long carbon nanotube. The paper was published in the famous "Nature" magazine in October 2019. Nature Communications"[4]. It took 6 years to gain just 10 centimeters, which shows how difficult it is to create this material.

Our goal is to create a length of more than 40,000 kilometers. There is obviously a huge technological gap that needs to be crossed, but this is no longer a bottleneck in scientific principles. What humans need is just Time and a little luck. I don’t know when humans will break through this technological singularity.

One day in the future, a huge floating platform will be built on the sea east of Indonesia's Lingamune Islands. This is the result of the joint efforts of more than 100 countries around the world*** Participated in the construction of the ground base station of Space Elevator 1. This platform is equipped with several aircraft carrier-grade engines that can push the platform to move along the equator, avoiding bad weather and adjusting the position of the cables to avoid possible collision risks.

There are two parallel tracks leading from the ground base station to space, and the ascending and descending elevators go their own way. Every 30 minutes, a 10-ton elevator will start to rise and return to the ground. From a distance, it seems as if the sky and the earth are connected by two shining necklaces.

The cost per ton of cargo transported to geosynchronous orbit has dropped to less than $50,000, and a wide variety of supplies and space tourists are being continuously sent to geosynchronous orbit. In space, various factories began to be constructed. It is even easier to assemble large equipment in weightless space than on earth, and more and more space sightseeing facilities with different functions and forms are being built.

At the same time, spaceships will be assembled directly in space, and the construction of the Earth's spaceport has also begun. Humanity will use the Earth's spaceport as a base to expand our space in space bit by bit. The territory of activities.

The blueprints for the construction of lunar ports and Mars ports have also been put on the agenda. This is the second era of great navigation in human history, and it will surely be a space age full of passion and fighting spirit.

At this point, Tsiolkovsky’s famous saying echoed in my ears:

The earth is the cradle of mankind, but mankind cannot live in the cradle forever. middle.

That’s it for your thoughts about space travel. At the end, I am going to announce today’s knowledge easter egg again.

Question:

What would happen if the cable of the space elevator broke?

If you are interested in this, I will continue to explain it to you in the "Future Mini Classroom", and the essence of the text will be integrated and online in the form of comics later. Please search the official account "Shanghai Pudong Development Bank" and reply with the keyword "Future Technology Experience Center" to enter the easter egg and listen to my explanation!

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