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Hyperloop – Fast, Cheap, Clean

Written By: 

Shalem Pravas

Representational Image of Hyperloop

Fig. 1: Representational Image of Hyperloop

The economic success of a nation depends prominently on its evolution in communication and transportation. Communication is steadily growing its speed, while the same cannot be matched by transportation. There are currently 5 modes of transportation; road, rail, air and sea. Out of these road and sea are quite slow, air is fast but expensive and rail is not as fast as it needs to be. Therefore there is a need to bridge the technological as well as an economical gap between a cheap mode of transportation (say, land) and a fast mode of transportation (like air). The first thought which would strike us is that of Bullet trains and Maglevs (Magnetic Levitation) trains. Although they increase the speed factor to quite a great extent (300 and 1000 mph respectively), does it meet the brief in terms of economics? Not necessarily, since high initial investments and maintenance costs. The simple point is that when the investments are high, it is right to expect it to give back a high level of returns.

Then there is the concept of supersonic flight. The problem with travelling at supersonic speed is the high friction losses between the gas molecules and the surface of the jet involved during the formation of shockwaves. So, in order to be more effective they need to travel at higher altitudes where atmospheric density is low (lesser number air molecules). Therefore it is a more optimum choice for longer distances where the plane would have more cruise time. Ground level supersonic travel also involves problems related to inertial and G forces at deceleration points and sharp turns. There have many projects which have aimed to bridge this gap dating back to the 1950s. One of those ideas which has been explored in this article is that of revolutionary entrepreneur Elon Musk (Tesla and SpaceX), the Hyperloop.

  1. The Design Concept


Image Showing Conceptual Design of Hyperloop

Fig. 2: Image Showing Conceptual Design of Hyperloop

The idea is inspired by the pneumatic tubes which are used to deliver mails or packages within the same building. They deliver an object by propelling it by creating a pressure difference in the tube. The pressure difference is created by maintaining one side in a low pressure (near vacuum) and the other side at a high pressure. The difference tries to normalize itself by trying redistribute the pressure. If an object is placed in between this boundary, it causes motion.

The Hyperloop aims to amplify this concept to create a large tube between two cities (initially between Los Angeles and San Francisco – 350 miles) and transport public through people sized capsules accelerated by magnetic fields. Once again, the problem with supersonic speeds is that it compresses the air column in front of so much that it creates changes in density, temperature, pressure etc. These changes cause a steep increase in friction between the surface and the gas molecules, which would make it a practically unfeasible concept. Therefore, it would be necessary to maintain the tube at a low pressure.

Another essential element of design of the Hyperloop is to address a problem which would cause choking of the flow. This problem will be caused by the relative areas of the tube and the pod. If the gap is going to be small between the wall of the tube and the surface of the pod, it would cause the air column in front to choke, i.e. the pressure difference would never be relieved. This can be looked at like a syringe, when the plunger moves forward, the column in front is also pushed forward, meaning that there is no backward leak. So why would this be a problem? Economics. This would cause a loss of useful energy, i.e. the force generated by the fan will also be involved in pushing the air column in front adding to the effective load.

The way this is solved is by adding an electric compressor to the front which would be involved in relieving the high pressure in the forward end of the pod. This would enable a smoother transition from low to high velocities.

The electric compressors would also solve the problem of friction between the walls and pod surface. Any sort of mechanical contact between the wall and the surface need to be avoided because of the role friction plays in adding to the power required. Therefore, the compressor could pump the sucked air radially outwards to create air cushioning to the pod. The process of the design is always to minimize the gap between the consumed power and work done.

Therefore the compressor works to solve two problems at the same time. The next requirement is to power it. A normal battery would be sufficient as long as it is not used to accelerate the capsule pod. To accelerate the pod, an external linear electric motor (which is a flat induction motor) will be used, similar to the product used in the Tesla Model S electric car. These linear accelerator motors are placed along the length tube which provide constant acceleration or deceleration as required

The best part of the development of the Hyperloop is the fact that its design is absolutely open source. All of its designs, economics, technical specifications, etc. are available online to everyone who is interested. This means that anyone can participate in discussions involved its conception. This would help the concept to absorb as many inputs (intellectual) to truly make it a success.

 2. Technical Specifications and Operational Features

The proposed initial setup for the Hyperloop is between Los Angeles, California and San Francisco, California, which is a distance of 350 miles. Current options of travel include air (fast, expensive, polluting), road (cheap, slow, polluting) and rail (cheap, slow, non-polluting). The proposed system of Hyperloop aims to combine (as much as possible) the best aspects of all the viable options. The main competitor project to Hyperloop is the “California High Speed Rail” which is the introduction of bullet trains.

2.1 Capsules

Diagrammatical Image of Internal System of Hyperloop Capsule

Fig. 3: Diagrammatical Image of Internal System of Hyperloop Capsule

Each capsule of the Hyperloop can contain 28 passengers (passenger module) or 28 passengers plus 3 vehicles (passenger plus vehicle module) which will depart at an average interval of 2 minutes with the shortest interval of 30 seconds at peak timings to accommodate 840 passengers per hour. Passenger unloading and offloading will take approximately 5 minutes. Initial operations require 40 capsules to meet the passenger requirement. The capsules will be separated in the tube by about 23 miles.

These capsules will be capable of travelling at high subsonic speeds of 760 mph (1220 kmph or Mach 0.99). The capsules will be aerodynamically streamlined to reduce drag forces and also to address the shockwave induced drag if the capsule reaches sonic speeds. The power requirement to overcome the aerodynamic drag will be 134 horsepower (at speeds of 700 mph) and a drag force of 320 N.

Suspension is done by the means of air bearings located at the bottom which spew out the compressed air from the compressor to the bottom surface of the tube at a pressure of 9,400 Pascals to support the weight of the capsule and passengers and float it on a thin film of air.

Graphical Image of Air Bearings in Internal Capsule of Hyperloop

Fig. 4: Graphical Image of Air Bearings in Internal Capsule of Hyperloop

2.2 Tubes and Propulsion System

Hyperloop Tube Section with Solar Panel

Fig. 5: Hyperloop Tube Section with Solar Panel

The tube will be made of steel and two tubes will be welded together to accommodate travel in both directions simultaneously. Pylon pillars will be placed every 100ft to support the tube structure. The power to the electrical systems will be derived from solar arrays which will be placed in top of the tubes. The pressure in the tubes will be maintained at 100 Pascals, which is one thousandth of atmospheric pressure at sea level. Pumps will be located in the tubes which will maintain the low pressure. This low pressure will reduce the drag force by 1000 times.

Linear Electric Motor

Fig. 6: Linear Electric Motor

The propulsion will be provided by linear accelerator motors (stators) placed at regular gaps in the tubes which will be captured by rotors on the capsules to transfer the momentum to the capsules. The stator – rotor combination will provide a linear thrust to the capsules.

  1. Worth It?

The best way of showing if a project will yield a long time success, apart from technical advances, is numbers and how they compare to the other options present in the hands of the consumer. The total proposed project cost for the Hyperloop is just under 6 Billion US$ (compared to its competitor’s project cost of 64 Billion US$) covering 2 tubes and 40 capsules. Remunerating these costs in 20 years’ time will lead to a one way trip to cost 20 US$ plus the addition everyday operating costs involved (compared to the air travel cost of $158, road trip cost of $115 and California high speed rail cost of $105). Also an efficient way to determine its economical stronghold is the energy cost involved in this project, i.e. the energy spent to transport one passenger through one journey, which is the lowest compared to the other modes involved (as shown in the figure shown below).  

Graph Showing Energy Costs Associated with Various Modes of Transportation

Fig. 7: Graph Showing Energy Costs Associated with Various Modes of Transportation

The founder of SpaceX and Tesla, Elon Musk, is known for pushing innovation and is a prominent figure in the technology scene. Whether it is the Tesla Wall (house powering batteries) or the Reusable Rocket Stage, he never fails to make higher end technology affordable to all classes as well as concentrate on green energy. All designs are released openly which make them open to useful debate keeping it open source. The Hyperloop is another one such concept which may mark him in future history books as one of our generation’s greatest inventor. The design and economics for the Hyperloop transportation system has been presented in an Alpha – Paper present on their website. The project is being undertaken by Hyperloop Transportation Technologies, Oerlikon Leybold Vacuum and Aecom, also with the joint efforts of engineers from Boeing and SpaceX.

Cross Sectional View of Hyperloop

Fig. 8: Cross Sectional View of Hyperloop