In 2013, under the call of "Iron Man" Elon Musk, the concept of hyperloop (a vehicle running in a vacuum tube) became widely known. In recent years, it has quickly become a scientific research and development center in many countries. hot topics of social discussion. But in fact, similar ideas had been proposed two hundred years ago.
This article will briefly review the evolution and history of vacuum pipeline transportation, and get a glimpse of the past and present life of the hyperloop.
The origin of vacuum technology is clearly recorded in history as Torricelli’s experiment in 1643: filling a long sealed tube with mercury and inverting it in a mercury tank will reveal that the relationship between atmosphere and vacuum The pressure difference between them can lift up 760 mm of mercury. The first case of the application of vacuum technology was the Magdeburg Hemisphere Experiment in 1654: two hemispheres were synthesized into a sphere with a diameter of 119 cm, and a vacuum pump was used to evacuate the internal gas. After that, eight horses on each side were unable to Pull away.
Magdeburg Hemisphere Experiment
It can be said that these two famous experiments both used the principle of huge pressure difference between the atmosphere and vacuum [1], and also this Proof that pressure differences can produce mechanical forces. Later generations also got inspiration for transporting items.
In 1799, a British mechanical engineer and inventor named George Medhurst applied for a patent for a fan pump that obtained power from compressed air. The following year, he applied for a patent for a "wind-driven" engine that uses compressed air to drive cars. At the same time, he proposed a wind-driven car service plan and suggested setting up pump stations on the driving route to continuously replenish power. This can be understood as Similar to the relationship between electric cars and charging piles.
Atmospheric Railway
Atmospheric Railway
Based on previous ideas, Medhurst proposed the idea of ??a vacuum mail line in 1810 and believed that this use The method of air pressure difference transporting letters and goods through pipes is faster and more efficient than a postman delivering them door to door. Further, he began to imagine the possibility of using larger pipelines to transport trains.
In 1812, he first published a theoretical calculation article on atmospheric railways, demonstrating the feasibility and effectiveness of erecting pipes with a diameter of several meters above the rails to quickly transport goods and passengers through air pressure differences. and advantages. In addition, he also conceived another form of atmospheric railway, which is to lay a long pipe under the rails. There are devices in the pipe connected to the train. The devices move driven by the air pressure difference, thus driving the train to move. The power source of the train Not the front of the car, but the pipes under the car body.
Shortly before his death in September 1827, he published the book "A New Inland Transportation System", which highly praised pneumatic propulsion and believed that this method could be used even without horses or other animals to provide power. Reached a speed of 96 kilometers per hour.
Atmospheric railway uses air pressure to move the car body along the track instead of using the front of the car as power.
However, due to various reasons, the atmospheric railway was not successfully implemented, and this idea was gradually shelved. Until 2018, an 89-year-old American engineer Max Schliger turned it into a reality: He set up a track in his vineyard. There is a 30 cm diameter polyvinyl chloride pipe between the rails. Attach a pump to remove air from the tube or to inject air into the tube.
Max Schliger's Atmospheric Railway
Under the influence of air pressure difference, the "thrust car" in the pipe drives the train connected to it through magnets to move. The model, which is only one-sixth the size of a standard rail system, has shown that it can easily overcome steep gradients that would be insurmountable by conventional trains, operate with less noise, require no overhead transmission lines, and can run pumps powered by renewable energy.
Max Schliger used a model of an atmospheric railway to demonstrate: blow air inward at one end of the pipe, and the train model will move forward under the pressure of the air.
In more than a century after Medhurst's death, the theoretical research on vacuum pipeline transportation gradually became deeper and more complete.
Moreover, this mode of transportation also shines in the emerging science fiction literature. The ideas in those works may seem advanced, but in fact, from a timeline perspective, they lag behind the theoretical research of scientists, and they all have their own theoretical prototypes.
In 1888, Jules Verne's son Michel Verne was inspired by the atmospheric railway and published the ultra-short story "Future Express". The novel imagines a steel pipeline laid on the bottom of the Atlantic Ocean, with a length of more than 4,800 kilometers, a diameter of about 1.5 meters, and a weight of more than 13 million tons, connecting Europe and North America. The pipes are wrapped in three layers of iron mesh and the outer surface is coated with resin to protect them from seawater activity.
Driven by strong airflow, the train in the tube can reach speeds of up to 1,800 kilometers per hour. It can reach Liverpool in two hours and 40 minutes from Boston. The advantages of this system are obvious: the inner surface of the pipe is finely polished, which has the effect of suppressing the nervousness of passengers; depending on the season, the air flow can be adjusted to equalize the temperature in the pipe; regardless of issues such as gravity and loss, the system's It's cheap to build and operate, so ticket prices are incredibly low.
Illustrations by artist A. J. Johnson for "Future Express"
However, atmospheric railways need to overcome air resistance and friction between wheels and rails, so the theoretical speed ceiling is low. In addition, even if the vehicle can reach a very high speed, the aerodynamic noise and aerodynamic vibration will become very large at that time, and the energy consumption will also increase significantly. Therefore, with the development of science, theoretical research is gradually moving in the direction of getting rid of friction and air resistance.
In 1904, Robert H. Goddard, the father of modern rocket technology, proposed the idea of ??vactrain, which was the first modern vacuum pipeline transportation system. At that time, he was still a freshman at Worcester Polytechnic Institute in the United States. He imagined that the train was sliding in a tube maintained in a vacuum state. In order to accelerate and decelerate the train through non-magnetic means, and to prevent friction, fluid pressure needs to be applied between relatively movable parts, such as wheels and rails, by spraying it with a nozzle. It emits high-pressure and high-temperature liquid, and the liquid immediately turns into high-pressure steam after being sprayed out, causing the car body to float on the track.
In essence, the train can be seen as running on a high-pressure liquid film. In 1906, Goddard perfected this idea in the short story "High Speed ??and Round Trip." Three years later, Scientific American published an overview of the work under the title "The Limits of Rapid Transportation."
Schematic diagram in Goddard’s vactrain patent
Goddard’s idea can be said to be the transition from atmospheric railway to hyperloop. Compared with atmospheric railways, the vactrain's pipes are in a vacuum state, and the trains no longer use air pressure differences to provide power. For the first time, consideration has been given to reducing air resistance and eliminating friction between the trains and the track. Compared with the hyperloop, the form of vactrain is very close to it. However, in terms of the means to levitate and move the train, most hyperloop solutions use magnetic levitation technology, while vactrain uses high-pressure gas.
In 1955, Polish science fiction master Stanislav Lem published "The Magellanic Clouds". This novel is set in a communist utopia in the 32nd century. Humanity has completed colonization of the entire solar system and is attempting interstellar travel. In the novel, Lem describes an intercontinental vacuum train called the "Organowiec", which can travel at a speed of more than 1,666 kilometers per hour in a transparent vacuum tube. This is obviously affected by vactrain.
Cover of "Mercenaries"
In 1962, American science fiction writer Mike Reynolds' short story "Mercenaries" published in "Analogy" even mentioned vacuum pipeline transportation. crucial location.
In the novel, peace has been achieved. In order to prevent the possibility of world destruction, the government stipulates that only weapons designed before the 20th century can be used in battles, and all battles will be televised to entertain the public. Major companies use mercenary armies to resolve business disputes.
In the transportation industry, mainland hovercraft companies have a monopoly. The newly emerged vacuum pipeline transportation company can significantly reduce transportation costs and provide consumers with better services, thus breaking the monopoly. But first, it has to fight a war with the former.
Of course, not only the weapons, but also the means of transportation in the novel are all ideas that existed before the 20th century. The concept of hovercraft can be traced back to 1716, when Swedish scientist Emanuel Swedenborg mentioned the word "levitation" when studying the surface effects of vehicles. By the beginning of the 19th century, some people realized that driving compressed air into the bottom of a ship could reduce sailing resistance and increase sailing speed. The concept of vacuum pipeline transportation can be traced back to Medhurst's idea of ??a vacuum mail line in 1810. Therefore, whether in novels or in real history, vacuum pipeline transportation is indeed newer than hovercrafts.
If previous research was mainly limited to theoretical calculations, then in the 1970s, Robert M. Salter, a fan of vacuum pipeline transportation, began to consider practical operational issues. At that time, he imagined a vacuum pipeline system "Planetran" located in solid rock formations hundreds of meters underground, running through major cities in the northeastern United States and setting up 9 stations in 8 states.
At that time, Japan's Shinkansen had been in operation for nearly 10 years, and research on maglev trains was also being carried out in various countries around the world, but the technology was not yet mature. Therefore, instead of applying magnetic levitation technology to his idea, he proposed using steel tires. The train uses electromagnetic force to accelerate, and deceleration is achieved by squeezing the thin air in front and accelerating the train in adjacent tubes. It can be seen as a fusion version of atmospheric railway and vactrain.
The most commendable thing about this system is its amazing energy-saving capability. As a "high energy conservation system", when the train decelerates, it will return most of the energy to the system for use by vehicles in adjacent pipes when accelerating. In addition, during the running of ordinary trains, the proportion of air resistance to the total resistance exceeds 70%, while the air resistance in the inner cavity of the vacuum pipe will be greatly reduced, and the energy consumption will naturally decrease accordingly, so that the energy cost consumed by each passenger is less than 1 US dollars, and the average speed of the entire journey can reach 4,800 kilometers per hour, taking only 21 minutes from the east coast to the west coast of the United States.
Salter believes that this system will help reduce the damage caused to the atmosphere by aircraft and ground transportation, and will have huge environmental and economic benefits. Therefore, he called Planetran the "logical next step" for the United States. However, its construction cost was estimated to be as high as US$1 trillion, so the plan was not adopted by the government.
As magnetic levitation technology continues to achieve breakthrough results, advocates of vacuum tube trains also realize that this may be one of the key factors in its success. In November 1991, Gerald K. O'Neill submitted a patent application proposing the idea of ??"magnetic flight": a train located in a tube would run on a single track instead of the traditional two rails. Permanent magnets are installed on the track, and the train equipped with variable magnets is suspended on the track under the action of electromagnetic force. He calculated that if the air was pumped out of the pipe, the train could reach a speed of 4,000 kilometers per hour.
As time enters the 21st century, the technology for obtaining vacuum has matured, and high-speed maglev trains have been put into use in Shanghai, China, Yamanashi, Japan, and other places. It looks like everything is ready for the Hyperloop. In 2013, feeling that the high-speed rail project in Northern California was slow, Tesla and SpaceX founder Elon Musk published a 57-page white paper proposing to build a 560-kilometer hyperloop between Los Angeles and San Francisco. idea.
In this system, the transport capsule runs at a speed of 1,220 kilometers per hour in a vacuum tube, and the energy for suspending the capsule comes from solar energy or other renewable energy sources. Interestingly, Musk envisions something similar to the aerodynamic levitation proposed by Goddard. It can be seen that the hyperloop is almost completely derived from the theoretical conception of previous scientists.
Since then, many companies and scientific research institutions have entered the research and development camp of hyperloop, including China Aerospace Science and Industry, the National Key Laboratory of Traction Power of Southwest Jiaotong University, Beijing Jiaotong University, and Xijing University and other domestic institutions. However, they all use magnetic levitation. Regarding the top speed that everyone is most concerned about, some organizations have also given data of 6,500 kilometers per hour. Whether it can be achieved is still unknown.
It is true that the hyperloop seems to be very close to the current level of human science and technology, but in fact there are still many key issues that need to be studied and solved -
It is precisely because the above and more have not been As mentioned, the hyperloop is still in the model testing stage and is far from reaching the stage of manned testing. Fortunately, it is completely feasible in theory, and there are more scientists around the world working on the problem than before, so there is still hope that it will become a reality.
It is worth mentioning that in the process of studying vacuum tube trains, scientists also imagined the possibility of using this method to accelerate aircraft. Because if a traditional rocket increases its payload, it must be made larger and more chemical propellant must be packed into it. Vacuum pipeline transportation is not only fast, but also saves energy. If used to accelerate the aircraft, the aircraft can be smaller or the load can be increased.
In 2001, James Powell, one of the inventors of superconducting maglev (the basic technology of modern maglev trains) in the 1960s and a researcher at Brookhaven National Laboratory in the United States, proposed the ambitious interstellar train ( StarTram, the magnetic levitation space launch system.
As the name suggests, this system requires placing a magnetically levitated spacecraft into a curved vacuum tube that stretches into the sky. The first-generation system has a pipeline length of 130 kilometers and an outlet height of 3 to 7 kilometers. The best places are the Andes in Chile or the White Sands Missile Range in southern New Mexico. After accelerating, the spacecraft can rush out of the tube at a speed of 14,300 to 31,500 kilometers per hour and escape the earth's atmosphere. This is very close to the second cosmic speed.
The interstellar train launches every hour, and each launch can carry more than 70 tons of cargo. In terms of launch cost per kilogram, the system only costs US$20 to US$50. You know, even SpaceX can only say that it will drop from the original US$4,600 to US$20,000 to US$1,400. In terms of construction costs, the first-generation system requires 20 to 40 billion U.S. dollars, which is far lower than the 196 billion U.S. dollars spent in the 30-year cycle of the space shuttle. It is even more negligible compared with the U.S. military expenditure of 643 billion U.S. dollars in 2018.
The research team plans that the first-generation interstellar train will mainly transport satellites and other cargo and will be completed in the 2020s. The second-generation system has a pipeline length of 1,000 to 1,500 kilometers and an exit height of 22 kilometers. It transports one million space tourists every year. Each ticket only costs US$5,000. It is planned to be completed in the 1930s.
Of course, the interstellar train not only faces the existing problems of the hyperloop, but also adds many extremely difficult engineering problems, such as the erection of pipelines, the suspension control of aircraft in pipelines, and so on. However, as soon as the interstellar train was proposed, it was verified by Sandia National Laboratory in terms of feasibility, and there are currently related theoretical studies and model tests. If the interstellar train can come true, it may bring mankind into a new space era.
[1]Human technological means cannot obtain absolute vacuum. The vacuum defined by academic circles is a relative state, which can be called a vacuum if it is lower than the atmospheric pressure, covering a wide range from one atmospheric pressure (about 105 Pa) to the absolute vacuum of nothingness (0 Pa).
[2] A measure of the rarefaction of a gas.
This article first appeared in the 2020 issue of "Science Fiction World" magazine, with the original title "From the Ground to Space - The Evolution of Vacuum Pipeline Transportation"