HyperLoopDesign is a resource for Hyperloop engineers, looking at the design challenges and solutions for final designs or sub-systems.
Hyperloop Alpha, where it all started
Elon Musk's proposed Hyperloop Alpha in August 2013, which ran in a 2.23m (7ft4") diameter tube, at an absolute pressure of 100 Pa ( 1/1000 atmosphere). It used air bearing skis, with an air compressor to provide air. Acceleration thrust was from linear motors on limited sections of the track.
Progress after 10 years
It is now 10 years since Hyperloop Alpha, Elon Musk proposed it as a open-source engineering project, and it has been a popular research subject.
The Hyperloop Pod Competition was sponsored by SpaceX who built a 1.8m diameter vacuum tube, 1.6km long. Over 100 student teams were involved, with some competing in the vacuum tube between 2017 and 2019. Initially most teams experimented with air skis, then maglev, which were both disappointing. Finally TUM (Warr) Hyperloop achieved an impressive 463 km/h, using small wheels clamped onto an aluminium rail.
There have been many prospective startup companies, but the only significant commercial project has been (Virgin) Hyperloop One, with a reported $485 million budget. They built a 500m long vacuum tube, and achieved 387 km/h un-crewed, and 172 km/h with 2 crew. Their technology is not published, but seems to be eddy current maglev onto an aluminium rail. In 2022 they announced a new focus on freight, not passengers.
Elon Musk has had no further involvement with Hyperloop, but is building tunnels with the Boring Company, which will transport electric vehicles, but without the vacuum.
The way forward
Hyperloop is an amazing project, it offers high speed transportation, with very low energy consumption, and overall project costs similar to high-speed rail. But it is a massive research project, with many areas of technology where we have little previous experience.
The levitation technology is the first hurdle. Hyperloop Alpha’s air skis would never work with the limited airflow in a near-vacuum. Maglev is certainly possible, as demonstrated by the Japanese SC Maglev, and the German/Chinese Transrapid train. But they have high energy consumption and unaffordable construction costs.
So we need to decide the levitation question, then push on with all the other technical challenges. Tube construction, airlocks, stations, passenger seating, vacuum pumps, cooling and safety. All the time we need to be conscious of the overall project building cost, it must be comparable to high-speed rail, or Hyperloop will never be built.
Cheetah is a design variation released by Richard Macfarlane in January 2014, with a number of changes to simplify and solve problems.
Wheels are used which provide traction. Steam from the cooling system is ejected into the tube, increasing the speed of sound, and reducing aerodynamic drag.
The pod is 3 seats wide, and the tube is now 2.6 - 2.8m diameter. The seats are in 3 seating modules which roll out at the station.
VacuuDuct - shorter pods that can combine into a train
Competition Pod - for the 2016 Pod Competition.
Wheels - the simpler and more achieveable option.
Elon Musk spoke at the 2016 Pod Competition, and recommended wheels.
Wheels have been proved at higher speeds than any other levitation
Pneumatic tires are the preferred option if achievable
Steel rim wheels on a resilient surface are a good alternative
Continuous traction is a great advantage
Wheel forces are analysed here
Maglev and air bearing skis
Hyperloop Alpha originally proposed air ski bearings for levitation. But there may be insufficient airflow in the near-vacuum. See air skis here.
Maglev using copper coils along the whole route would be the ideal levitation system, except for the extreme expense. See maglev coils here.
Wheel research and development
A considerable budget is available for wheel research, as $billions can be saved in the cost of a simple tube without rails, linear motors etc.
Rolling road test rig can be used for initial research.
Full speed pod testing would need a test track at least 45km long.
A CFD study is important to study aerodynamic drag.
Station layouts, airlocks and passenger loading
A Hyperloop station needs to be different from a train station, because of the vacuum and the structural requirements of the pressure hull.
Side doors on the pod, why they are not feasible
Mobile seating modules that travel to the passengers
Cooling using steam
Cooling is very efficient by boiling water, and ejecting the steam into the tube
Steam has a higher speed of sound, reducing the Mach no. of the pod, reducing aerodynamic drag and shock waves
Steam in the tube reduces vacuum energy cost
Vacuum pumping energy is greatly reduced, because the steam only needs to be pumped to a low-pressure condenser
The Natural Steam Vacuum is a very low energy solution for 3kPa pressure
Vacuum pumps and initial evacuation. Choosing suitable vacuum pumps, and calculating the energy cost of the initial tube evauation, and airlock pumping
Kantrowitz - there is no limit
Hyperloop Alpha proposed that there is a definite limit to speeds inside a tube, depending on the tube/pod area ratio, but this falsely used incompressible flow theory at high speeds. External compression is a much lower energy solution, than the complex compressor of Alpha.
The vacuum tube is the heart of Hyperloop.
It is by far the biggest expense, and the quality of it affects the experience for the passengers.
Hyperloop’s greatest challenge is to provide smooth bump-free travel at high speeds.
It is likely that the maximum speed is limited by the achievable accuracy of the tube.
A resilient suspension system is important