But in my opinion, such space tourism has not really left the earth, and we are still active within the gravity of the earth.
This time, I'm going to push this topic forward. I really want to talk to you: is it possible for human beings to really leave the earth and go to the moon or Mars for a holiday in the foreseeable future? Or further, can ordinary people go for a ride to Jupiter, Saturn or even Pluto based on the moon or space station? Are there any key technical singularities in the aerospace field? Once we break through this singularity, will there be a big explosion in our space industry?
The most difficult thing in the space industry is to get rid of the gravity of the earth. We can imagine the earth as a gravity well, and we humans are frogs at the bottom of the well. As long as we can jump out of this well, there will be a Ma Pingchuan outside and the vast universe will soar. Why did Ma Pingchuan jump out of this well? Because sailing in space is actually very energy-saving, because there is almost no resistance in vacuum, the spacecraft only needs to consume fuel when accelerating, decelerating and changing orbit, which is nothing compared with the fuel needed to overcome the gravity of the earth.
The only technology that humans have mastered to jump out of the gravity well is rocket technology, but the biggest problem of rockets is that the launch cost is too high. One of the biggest reasons is that in the past, rockets were disposable consumables, and it took tens of millions to hundreds of millions of dollars to build a rocket. For example, a rocket launch is like a local tyrant buying a Boeing 737, throwing it away once and buying another one next time. How many local tyrants can there be in the world?
Therefore, in order to reduce the cost of rocket launch, whether it is Elon Musk's Space Exploration Company, Virgin Galactic Company or Blue Origin Company, what they do is to try to recycle the rocket.
In early 2020, Christopher Couluris, director of vehicle integration at Space Exploration Technologies, said at a briefing that the single launch cost of recoverable Falcon 9 may eventually be reduced to $28 million [1]. What is this concept? The recoverable Falcon 9 has a maximum load of about 30 tons, with a price of $930,000 per ton, which is almost 200 times the current price of ordinary air transportation. You may not realize the difference of 200 times at once. For example, the difference between your monthly salary 1000 and your boss's monthly salary of 2 million.
Virgin Galactic, another space travel company, has even started selling tickets for space travel. According to SEC document [2], Virgin Galactic intends to send a group of tourists into space every 32 hours before 2023. Although this so-called "space tourism" is actually like sitting in a shell, just taking a look at the height above the surface 100 km, and then quickly falling back to the surface, the fare is as high as 250,000 US dollars/piece. Richard branson, the founder of Virgin Galactic, is the most optimistic estimate: after 10 years, the fare can be reduced to less than 50,000 dollars, and another company named Blue Origin, which announces the fare of space tourism, is similar.
Hearing this, I estimate that many people will compare the aerospace industry with the traditional transportation industry, and may think that large-scale production will inevitably bring about a rapid decline in costs. As long as the market of space tourism can be continuously cultivated, the fare should be lower and lower until all ordinary people can afford it, just like cars, ships and civil aviation planes in those days, didn't they all go through a process from the rich to the ordinary people?
The problem is-space launch is really not as simple as you think. In order to make it clear to everyone, today I will tell you a few high-end goods.
There is a famous rocket equation, which was put forward by Russian scientist Konstantin Ai Du Aldovich tsiolkovsky, who is known as the father of human rockets. This rocket equation is like a safety circle drawn by the Monkey King for Tang Priest. No matter how the technology is improved, the human rocket can't jump out of its defined cost performance.
Before explaining this equation, let's look at the essential differences between rockets and cars, ships and planes.
First of all, only rockets need to constantly defying gravity in the process of movement, and other vehicles basically don't need defying gravity in the process of movement. In a more popular way: the rocket moves vertically upward relative to the ground, while other vehicles basically keep horizontal movement. Don't underestimate the essential difference brought about by the different directions of this movement. Let me explain something to you:
The resistance that a car has to overcome during driving is mainly the friction from the ground. Friction mainly depends on the rolling friction coefficient between the tire and the ground, and has little to do with the weight of the car itself. For example, on an ordinary urban road, the rolling friction coefficient is about 0.02, which means that if the weight of a car doubles, the friction will only increase 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 ships have to overcome in the process of movement mainly comes from the resistance of water to ships. The water resistance mainly depends on the speed of the ship and the contact area between the ship and the water, and has little to do with the quality of the ship itself. The calculation formula is more complicated, but the conclusion is similar to that of a car. The greater the ship's deadweight, the lower the energy consumption per unit weight. So ocean-going ships are getting bigger and bigger. If it weren't for the lock restrictions of several major straits in the world, we would make the transport ship bigger.
The resistance to be overcome by aircraft in the process of movement mainly comes from air resistance, which is similar to the resistance encountered by ships in water, and the conclusion is similar: the greater the passenger capacity of aircraft, the lower the energy consumption per unit weight.
Therefore, the cost performance of vehicles such as cars, boats and planes can be summarized in one sentence: the larger the vehicle, the higher the cost performance.
However, when it comes to rockets, this rule is broken. Because the rocket needs to move upward against gravity, the biggest resistance the rocket encounters is gravity, and the magnitude of gravity is almost only related to one thing, that is, the mass of the rocket. The greater the mass of the rocket, the greater the resistance to be overcome. But paradoxically, the fuel itself that powers the rocket is huge. The more fuel you add, the more fuel you need to consume to send it to the sky. This is a bit like the logistics team that sent grain and grass in ancient times. The more people and animals there are, the more food and grass they will eat. In this way, it will be very complicated to calculate the relationship between the fuel load and the payload of the rocket.
The first person to realize and clarify this complex relationship is tsiolkovsky, whose rocket equation is also called tsiolkovsky rocket equation. To deeply understand the current predicament of human space technology, we must first deeply understand the rocket equation.
I want to ask you not to be afraid. This equation is not difficult to understand. The next few minutes, although some high-energy, but as long as you concentrate, you will be able to understand. Once you understand it, you will get great pleasure in understanding the principle.
This equation approximately describes the relationship between the initial total mass m0 when the rocket takes off and the remaining pure mass m 1 after the rocket burns out the fuel. The relationship between them is a linear function, and if it is written as an equation, it is:
m 1 = am0
If we replace m 1 with the familiar y and m0 with the familiar x, it will be written as follows:
y = ax
What is the image of this linear function in cartesian coordinate system? It's simple. It's just a straight line through the origin. If the coefficient a= 1, then it is a straight line with a slope of 45 degrees.
The slope of this straight line depends on the value of coefficient a.
If a 1, the slope is greater than 45 degrees.
This 45-degree slope is like a watershed. If the slope is exactly 45 degrees, it means that if X doubles, then Y doubles, and the two increase or decrease in proportion. However, if the slope is greater than 45 degrees, that is, A is greater than 1, then X is doubled and Y is more than doubled. On the other hand, if the slope is less than 45 degrees, x is doubled and y is less than doubled.
We have previously set that Y is equivalent to the pure mass left after the rocket fuel is burned, and X is equivalent to the initial total mass of the rocket. That is to say, whether the value of this slope a is greater than 1 or less than 1 determines a key question, that is, whether the initial mass of the rocket can be doubled, and whether the remaining pure mass of the rocket fuel can be doubled or decreased. Generally speaking, the bigger the rocket, the more cost-effective, or not, depending on whether the value of lethal coefficient A is less than 1 or greater than 1.
The greatest contribution of tsiolkovsky, the father of the rocket, is 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 mathematical relationship between the coefficient A and these two parameters?
Because our purpose is to study whether the approximate value of this A is greater than 1 or less than 1, I will explain and calculate this formula and analyze the range of this formula.
To calculate the value range of this a, we need to divide it into the following three steps:
Well, the calculation is over. Through these three steps, we can calculate the value of coefficient a ... because the previous value has been simplified, the actual value of a is about 0.05.
Therefore, the relationship between the initial total mass m0 when the rocket takes off and the pure mass m 1 after the acceleration of the rocket can be approximately written as follows:
m 1 = 0.05m0
What is this concept? Let me explain it to you, which basically means: when the fuel weight of a rocket is doubled, the payload of the rocket can only be increased by 0.05 times; In order to double the payload, the rocket needs to increase the fuel by 20 times.
Does this conclusion surprise you? This is the biggest embarrassment and dilemma facing human rocket-based space technology at present. We have to work 20 times harder to get a return of 1 times. You know, it is impossible to increase fuel by 20 times. More fuel means that the cavity filled with fuel should be made bigger and heavier. The requirements for cavity materials, engineering manufacturing technology and control technology will increase proportionally, which will lead to the rocket becoming heavier and heavier and requiring more fuel, which is a bit like a vicious circle.
In human history, the rocket with the strongest carrying capacity so far is Saturn V, which sent Apollo to the moon. Its self-weight has reached an astonishing 3000 tons, but it can only send 140 tons of things to the earth's low-earth orbit at most. This is the fundamental reason why space launch is so expensive, because the effective utilization rate of rocket fuel is too low.
At this point, we can draw a conclusion: as long as rocket technology is still used in our space launch, unfortunately, in the foreseeable future, it is impossible for ordinary people to realize their dream of space tourism. Space tourism can only be the entertainment of the rich forever. By the same token, because the cost cannot be reduced, it is wishful thinking to build a space station on a large scale, and it is too expensive to send things on the ground into space.
In order to really reduce the cost, we must find another way to get rid of the confinement of tsiolkovsky rocket equation to human space industry. Getting rid of the rocket equation is to separate energy from load-fuel (or substance that provides energy) does not need to rise with load.
At present, there is only one way with the scientific theory that human beings have mastered.
The essential difference between an elevator and a rocket is that the energy provider and the load are completely separated. The elevator can rise by electricity, has no mass, is completely independent of the rocket equation, and consumes the same energy as the skyscraper elevator.
Tsiolkovsky, the father of the rocket, is still the earliest initiator of the idea of space elevator. As early as 1895, he formally put forward the basic principle of space elevator.
In the simplest terms, the principle of a space elevator is to hang a long rope on a geosynchronous orbit satellite until it reaches the ground. Because the geosynchronous orbit satellite is synchronized with the earth's rotation, in theory, the place where this rope touches the ground can be fixed somewhere at the equator of the earth. If the elevator can be lifted by 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 equator of the earth, so the mass of a 36,000-kilometer-long rope will be quite large, so the concentric center of the rope and the synchronous satellite is below the height of the geosynchronous orbit, which cannot guarantee that they are synchronized with the earth's rotation as a whole.
To solve this problem, we need to lengthen the rope to the top of the satellite, and then connect a huge counterweight object, so that the concentric centers of all the connected objects just fall on the geosynchronous orbit. If you still don't understand here, you can have a look at my attached schematic diagram, which can help you quickly understand the principle and structure of the space elevator.
Scientists imagine that we can capture a near-earth asteroid from space, act as a counterweight in this structure, or collect all kinds of abandoned satellites left by humans in space. In a word, there is no fundamental technical problem here. Even if you keep sending things up by rocket, it's a one-time investment, no matter how expensive. If you use the keyword "space elevator" on the famous paper retrieval website Science Direct, you can find more than 30 papers with this keyword in their titles. Space elevator is not only a hot topic in science fiction, but also a serious topic that scientists have been discussing.
The real difficulty in building a space elevator is this cable over 40,000 kilometers. What material should we use to make this cable?
Our material requirements for this cable are that its own quality must be very, very light and its tensile strength must be very, very high.
In materials science, the unit of material strength is "Yuri", that is, the ratio of ultimate force per unit area to material density. The strength of titanium alloy commonly used to make glasses legs is about 300 thousand Yuri, and the strength of Kevlar, a super-strong material invented by DuPont Company in the United States, is about 2.5 million Yuri. According to the calculation, the strength of the cable for the space elevator should be between 30 million and 80 million Yuri.
What material can achieve such high strength?
In fact, this substance has been discovered by human beings. We mentioned in the previous program about new materials that graphene is rolled into the shape of a cylinder, that is, carbon nanotubes. Microscopically, carbon atoms are arranged like straws, and the diameter is smaller than that of hair filaments. But the strength of the material will decrease with the increase of the thickness of carbon atoms. In order to obtain the highest strength, it is necessary to manufacture carbon nanotubes formed by single-layer carbon atoms. If the process is perfect, in theory, the strength of single-layer carbon nanotubes can reach the level of 50 million to 60 million Yuri, which is enough to be used as a cable for space elevators.
At present, there are also materials called carbon nanotubes on the market, but those can't be called real carbon nanotubes because the carbon atoms are not fine enough.
20 13 professor Wei Fei of Tsinghua University, China successfully manufactured the longest carbon nanotube in the world at that time, with a length of about 0.55 meters. This achievement was published online in the internationally renowned journal of materials science, American Chemical Nanometer [3]. Six years later, in 20 19, Professor Wei Fei's team improved the world record by 10 cm, and manufactured carbon nanotubes with a length of 0.65 m. The paper was published in the journal Nature Communication [4]20 19+08. It took six years to increase 10 cm, which shows the difficulty of making this material.
Our goal is to create a length of more than 40,000 kilometers. Obviously, there is still a huge technical gap to be bridged, but this is no longer a bottleneck in scientific principles. All human beings need is 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 Lingamiunai Islands in Indonesia. This is the ground base station of the 1 space elevator, which was jointly built by more than 100 countries all over the world. This platform is equipped with several aircraft carrier-class engines, which can push the platform to move along the equatorial line, not only to avoid bad weather, but also to adjust the position of cables to avoid possible collision risks.
From the ground base station to space, there are two parallel tracks, and the elevator goes its own way. Every 30 minutes, an elevator with a load of 10 tons will start to rise and return to the ground. From a distance, it seems that heaven and earth are connected by two shiny necklaces.
The cost per ton of goods transported to geosynchronous orbit has dropped to less than $50,000, and various materials and space tourists have been continuously sent to geosynchronous orbit. In space, various factories began to be built. It is even easier to assemble large-scale equipment in weightless space than on earth, and more and more space sightseeing facilities with different functions and forms have been built.
At the same time, the spacecraft will be assembled directly in space, and the construction of the Earth Space Port will also start. Based on the Earth Space Port, mankind will gradually expand our activities in space.
Blueprints for the construction of the Moon Port and the Mars Port have also been put on the agenda. This is the second era of great navigation in human history, and it is bound to be a space age full of passion and fighting spirit.
At this point, my ears echoed with tsiolkovsky's famous saying:
The earth is the cradle of human beings, but human beings cannot live in the cradle forever.
So much for the imagination of space travel. Finally, I'd like to announce today's knowledge egg.
Ask questions:
What happens if the cable of the space elevator breaks?
If you are interested in this, I will continue to explain it to you in the "future small class", and the essence of the text will be integrated into it in the form of comics. Please search the official WeChat account "Shanghai Pudong Development Bank", reply to the keyword "Future Science and Technology Experience Hall" and enter the egg to listen to me!
# Space travel #