The man revolutionizing electric cars is now going after planes and trains, too. Elon Musk is developing the Hyperloop. How Would it Work? Essentially, it鈥檚 a sealed, reduced-pressure tunnel carrying passenger cars riding on a cushion of air propelled by linear electric motors. Musk tackles two of the most essential problems to high-speed travel: air resistance and friction. The air pressure inside the tubes would be reduced to one millibar or 1/1000 the atmospheric pressure at sea level. Less air pressure equals less air resistance. Theoretical transportation systems have involved 鈥渆vacuated" or 鈥渁irless" tunnels. Maintaining a vacuum over large distances is quite difficult and exposes passengers to dangerous decompression. Friction is reduced by removing wheels and any contact with the tube. Maglev trains achieve this by using magnets to push the car away from the track. The Hyperloop cars would run on air-cushion skis. Air would be pumped through a myriad of small holes in the skis, lifting the car from the tube.
Since the tube is at a near vacuum, not much air pressure would be required to lift the car from the tunnel. Another hurdle is choked flow. Even at low pressure, a car moving at high speed compresses air in front of it. Pressure builds and slows the car. To combat this, each Hyperloop car would have an air intake and compressor in its nose. The car would pull air in then propel in out the back. Some of this air would be diverted to the air skis underneath. This reduces pressure ahead of the car and produces thrust. The size of the tube in relation to the size of the car is also important. Air must have space to move around the car. To control cost and the size of the system, designers will want to keep the tubes small, so just the right ratio is essential. The idea of trains operating within tubes is not new.
In 1812 British engineer George Medhurst published Calculations, in which he describes a method of moving people and cargo with air propulsion through sealed tunnels. This idea was used in 1864 for the Crystal Palace pneumatic railway in London. Trains were pulled or pushed along a railway by large, steam-powered fans. In 1869, the Beach Pneumatic Transit system operated in New York City. This one block underground prototype was the city鈥檚 first attempt at a subway system. The train was moved by pressurizing the rear of the tube and decreasing pressure at the front. Financial support of the project faded before a full-scale version was approved. Magnetic levitation trains currently operate in China, Japan and South Korea. Throughout the world, they are being studied and considered. The highest speed ever for a maglev train is 361 miles per hour, which was achieved in Japan at the Yamanashi test track. The work of Robert Goddard, who invented the liquid fuel rocket, seems to predict the Hyperloop. In the early 1900s, he wrote about nearly every aspect of Musk鈥檚 plan, including reduced air pressure, choked airflow and air bearings. He did not imagine linear electric motors, although scientists coming after him did.
Continuing with Musk鈥檚 description of the project, the individual cars of the Hyperloop system will be similar to the Concorde Supersonic Transport. Each will be a sleek cylinder with exceptional aerodynamics. Behind the air intake and compressor will be a sound-deadening firewall and then the passenger cabin. The seats will be similar to those used on airplanes. They will be arranged in 14 rows of two. Unlike the Concorde, the Hyperloop cars will be much simpler, requiring no engines, wings or steering mechanisms. A rail gun is a futuristic weapon that uses a pair of electromagnetic rails to fire bullets at amazing velocities. The US Navy used an experimental rail gun to fire a seven-pound projectile at Mach 7. The technology can also be used to launch payload into space. The Hyperloop places the electromagnetic portion of the rail gun system in the floor of the tunnel, but only where necessary.
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