You might have been hearing a lot about a technology called Hyperloop in the news lately – a super-fast transportation system that could make long cross-country train journeys a thing of the past.

The Hyperloop system is a concept proposed by technology entrepreneur Elon Musk, whereby trains can travel at supersonic speeds up to 800mph (1,300km/h) using reduced pressure tubes. Pressurised capsule pods (the train carriages) ride on an air cushion in steel tubes driven by linear induction motors and air compressors, which allows them to go faster than current trains.

However, before Musk highlighted the technology in 2012, it was originally conceptualised and prototyped by American inventor Alfred Beach in the 19th century, and continues to be researched in the hope that it will eventually be commercially and technically viable.

However, Musk is not interested in commercialising the technology all by himself, so instead several startups are working on different methods to make it work, and Musk's private space company Space X is holding a competition to encourage engineers and students to design and develop prototype pods that can be be tested on SpaceX's Hyperloop test track in California.

So what are the differences between all the Hyperloop technologies and how do they work? IBTimes UK explains:


Hyperloop One – Musk's "air cushion" concept


Hyperloop One is a startup trying to develop a superfast route between Los Angeles and Las Vegas with a team of over 100 engineers working on the technology and has raised over $35m (£24m) in working capital.

Hyperloop One aims to commercialise the open source Hyperloop design created by Tesla and SpaceX engineers. Several people who work for or have worked for Musk in the past are co-founders. The design involves using air bearings to create an air cushion, similar to the way an air hockey puck floats, except that propulsion comes from jets of air being expelled from the puck.

In order to generate the air, the capsule pod travels through the tube at a high speed to generate the air needed, while at the same time an electric air compressor in the front of the capsule pumps air to the back of the capsule.

On 11 May, Hyperloop One conducted its first public high speed propulsion test on a 1.9-mile-long test track in the Nevada Desert, demonstrating that a lightweight aluminium sled could travel 100mph in just 2 seconds.


Bullet train technology – Magnetic levitation


Today, high-speed bullet trains in Germany, Japan and China make use of a technology known as magnetic levitation (maglev), whereby electricity is used to chill superconducting electro-magnet beneath the train cars to super cold temperatures so that they cause trains to hover above the tracks and propel the trains forward.

At the same time, two separate sets of electromagnetic coils in the track control levitation and propulsion by interacting with the magnets under the train car. By removing friction between the train and the track, the train can go much faster than before, and the current world record speed stands at 581km/h.


Hyperloop Transportation Technologies – Passive magnetic levitation


Hyperloop Transportation Technologies (HTT) is a startup made up of 500 part-time engineers across the US keen to develop routes other than from Los Angeles to Las Vegas. On 9 May, HTT announced that it had licensed a new technology known as passive magnetic levitation to make Hyperloop work.

Unlike maglev, passive magnetic levitation does not require superconducting magnets of powered electromagnets, so it does not require complex and expensive infrastructure upgrades. Instead, the technology works by using powerful permanent room temperature magnets.

The Inductrack system features train cars that have flat rectangular magnetic bars underneath them known as the Halbach array. The magnets are arranged in a special pattern whereby the magnetic orientation of each bar is at right angles to the orientations of the adjacent bars, and when the bars are placed in this configuration, the magnetic field lines combine to produce a very strong field below the array of magnets.

In order to get the train to move, the magnets in the Halbach arrays induce currents in the coils of insulated wire that have been embedded into the track. This generates an electromagnetic field repelling the magnets that causes the train to levitate above the tracks. However, at the moment, the levitation only works if the train is moving slowly.