How do Vacuum Tube Trains Work

Magnetically powered capsules that speed through vacuum tubes at 370 mph may be the salvation of commuters, thanks to a U.S. visionary and a Chinese university; they are developing a cutting-edge vacuum train capable of handling as much traffic as a 32-lane highway.

At quitting time every day in New York City, thousands of people pack into buses, cars and trains. But in a brand-new terminal, six people enter a wheel-less cylindrical train car and settle into their seats. The door closes, and the vessel slides silently into an evacuated, or vacuum, tube. A snapping sound outside indicates that the tube’s magnetic field has been activated, and the car shoots off like a bullet. In just 17 seconds, it’s speeding along at 370 mph. The passengers disembark at a station in Washington, D.C., after 30 minutes — instead of the three hours that the trip would have taken via conventional train.

At least, this is how Daryl Oster, founder of Evacuated Tube Transport Technologies (ET3), envisions the future of commuting. His patented design for a vacuum train — which is now being developed further by scientists at Southwest Jiaotong University in Chengdu, China — combines airless tubes with maglev (magnetic levitation) technology, which replaces wheels and rails with a strong magnetic field. If all goes as Oster intends, he may well have pioneered the transportation of the future.

Vacuum Tube TrainsThe concept of vacuum-tube trains — or other tube-based transportation systems — is not new. But previous attempts have used trains that run on wheels or on a magnetic rail. Thanks to magnets, ET3’s light passenger capsules float through the tubes with no resistance from either the air or contact with the surfaces in the tube. In other words, nothing is impeding the capsules from moving at a very high speed, which helps to keep energy consumption low.

The thermos principle

ET3 systemUsing a perfectly calibrated computer system, the capsules can be launched at very short intervals without colliding. The capacity of one tube would thus equal a 32-lane highway.

Oster compares the ET3 system to the way the Internet works: Tiny packets of information, each equipped with an address, find their own way through the network as they speed through heavy traffic. The same principle will apply to the train capsules: Each will have a unique numeric code, so when a passenger enters a destination, the computer will direct the capsule to the appropriate tube. As the system grows, it will consist of a large network of tubes.

The system will not include switch tracks like those used on conventional railways; instead, the capsules will behave more like cars weaving along highways. When the capsule approaches a place where the tube divides, a magnetic navigation system will give it a tiny push into the right tube at full cruising speed.

Oster claims that it is easy to produce the airless tubes that are necessary for his system to work. A system of pumps will suck the air out of very strong tubes that are capable of withstanding the pressure that is generated. Oster notes that we have plenty of experience with vacuums, which are used in everything from thermoses to televisions. The latter are so airtight that they can maintain a vacuum for years —just like the planned tubes that will hold the train capsules.

Passenger considerations

traveling in a vacuumBecause the capsules will be traveling in a vacuum, they can’t give off heat, thus they must be equipped with a cooling system. The capsules’ cabins will need to have pressurized air to accommodate passengers, just as the cabin of an airplane does.

In the event that a capsule stops during a trip, an emergency system will supply the passengers with air — again, like modern airplanes do. The affected portion of the route can be closed off so that air is directed into the tube via valves in order to normalize the pressure and allow the passengers to be evacuated. And this will all need to happen at a speed that allows the other capsules in the tube to slow down by air resistance.

Oster has painstakingly determined the tube’s optimal dimensions to be 5 feet in diameter. This will accommodate capsules that are similar in size to a large passenger car, but with three rows of seats. His design for the capsules allows them to be very lightweight.

However, unlike a car or a conventional train, the capsule’s passengers will not be able to look out at their surroundings as they hurtle through the tubes. To ease the likely discomfort this will create, Oster envisions outfitting each capsule with virtual windows — displays that can show films, television shows or other entertainment to occupy passengers’ attention during the trip.

Superconductive magnets

major advantage of the proposed ET3 systemA major advantage of the proposed ET3 system is that it consumes a minimal amount of energy, thanks to superconductive magnets developed by Chinese scientists. These electromagnets are made from superconductive wire that does not generate electrical resistance as long as it is kept below a certain temperature. The magnets also produce a powerful magnetic field without wasting energy in the process. Because its momentum will not be slowed by air resistance, the capsule will not need to be supplied with additional energy once it reaches its cruising speed. And 90 percent of the energy that the capsule uses will be recovered via electromagnetic induction when it slows down. Oster estimates that, per passenger, the ET3 system will consume just 1 percent of the energy used by an electric train.

In order to achieve superconduction, the magnets must be kept sufficiently cool. This is typically done with liquid helium, but the Chinese scientists have been able to achieve the same result using liquid nitrogen, which is much cheaper. And because the magnets are encased within an airtight environment, only a small portion of nitrogen is required per capsule to cool the magnet that keeps the capsule afloat.

As the polarity of the magnetic field alternates, it pushes and pulls the capsule to the desired speed. Oster is now trying to find a receptive partner in the United States to build a three-mile test track, preferably in a location where the system could eventually be extended to link two major cities that are 185 to 375 miles apart, such as Boston and New York City or the Big Apple and Washington, D.C. But any stretch frequented by 12,000 cars a day would work.

Global perspective

Vacuum trainOster recognizes that there is still much work to do, including developing all of the system’s details, so, in the spirit of open-source software systems, he has invited anyone to participate.

Despite the looming challenges, Oster remains optimistic. He is convinced that, in the long run, vacuum-based transportation will link the world in a new way — provided that the system’s components adhere to a global standard, it can be used across national borders. He also notes how quickly new systems can become commonplace: Less than 1 percent of Americans relied on a car in 1907, but within 35 years that number had climbed to 90 percent. And although maglev technology is in its infancy, Shanghai has a maglev train that operates daily.

Oster’s vision is catching on. In July, PayPal and SpaceX founder Elon Musk announced that his Tesla Motors operation would begin working on a fifth means of transport in addition to cars, ships, trains and planes. His idea? A tube system that ferries passengers between cities at high speeds — and he has invited scientists and engineers worldwide to contribute to its development. Why ET3? Evacuated Tube Transport Technologies

Version 2.0 boasts a speed of 4,000 mph

If the ET3 system becomes a reality, at some point the continents could be linked by a vacuum pipeline. Oster thinks that a pipeline buried underground could accommodate capsules traveling at speeds up to 4,000 mph, meaning that passengers could go from Beijing to New York City in as little as two hours. The tubes could also cross bodies of water if two vacuum tubes were encased in a larger tube that functions as a floating tunnel. Ultra-efficient 4,000 mph vacuum-tube trains