Scientists explain why Hyperloop is so dangerous and difficult

In just a few weeks, Musk’s “Boring Company” will test a short Hyperloop track in Los Angeles, but it's still not clear whether Hyperloop will be much use to anyone
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Hyperloop, the much-hyped uber-fast and futuristic vacuum tube transportation system, is inching closer to reality - according to tech entrepreneur Elon Musk. He first began to push the concept in 2012, although the idea goes back more than a century. In 2016, he launched The Boring Company to build tunnels under Los Angeles, which he said would become network of vacuum tubes to move passenger pods at high speed; he called the concept Hyperloop, because the tubes were originally supposed to run in a circle. He also encouraged companies and universities to start developing their own Hyperloop technologies.

Now Musk has announced - on Twitter, as is his way - that for the first test track is almost done, and will be ready for tests from December 10. So shall we get the champagne ready to celebrate the future of transport?

Not so fast, says Chris Bannister, associate professor in automotive engineering at the University of Bath. "Even if the trials go well, there would be significant challenges to rolling out this technology on a larger scale - not to say it isn't possible, but it would be difficult."

If the initial tests are successful, it is likely that Hyperloop will replace specific train routes, but long distances may be a long way off. "Unless it's an evacuated [vacuum] tunnel - which I doubt - it may not demonstrate anything new in a technology sense," says Roger Goodall, an engineering professor at Loughborough University.

There are multiple reasons why the first Hyperloop test is likely to fall short of its promise. First, infrastructure. For the technology to be viable, any Hyperloop system needs extensive infrastructure - and building that costs a lot of money. Any large-scale implementation of electric cars would face the same obstacle, says Bannister. "We have seen how difficult this is with charging stations for electric vehicles, but with Hyperloop the cost would be significantly higher. Overground routes could be problematic in urban areas, so would be required to be underground, which further adds to the cost."

Another technological challenge for a full-scale Hyperloop is maintaining the vacuum within the Hyperloop system, as any air leaks will impact the pods' maximum speed. There would have to be large vacuum pumps positioned periodically throughout the route to maintain the vacuum, and these will need to be powered. But building a hundred or so mile-long vacuum or near-vacuum chamber is almost impossible, says Phil Mason, a British scientist currently at the Institute of Organic Chemistry and Biochemistry in the Czech Republic - adding that the two core problems are expansion issues on a straight tube and atmospheric pressure.

"Expansion issues on a long straight vacuum tube are a nightmare," he says. Any large piece of infrastructure expands and contracts as the temperature and atmospheric conditions change, and that could be a major problem for Hyperloop. There are expansion issues even with bridges that don't have vacuums, and pipelines, for instance, get around them by building in space for the pipes to expand. This is not possible if one wants to travel through the tube at the speed of sound, though. For a 1000km-long Hyperloop, the tube length will vary by a few football fields between a hot and cold day.

Take humans. Atmospheric pressure is about 10 tonnes per square metre, with a typical human having about two square metres of skin. However, we don't notice that because the pressure is both on the inside and outside. If you have 10 tons per square metre pushing on the outside of the Hyperloop, and nothing pushing on the inside, there is a risk of a vacuum collapse - essentially the tube being crushed by the atmosphere, says Mason.

"Humans do not suffer a vacuum lightly. In the event of decompression, there won't be any oxygen masks to keep you alive," he says. "The Hyperloop takes all the hazards of being in space and brings them down to a few cm of the Earth's surface. It also brings all the hazards of the speed of planes and combines it with the hazard of traveling within a few cm of the earth. Any Hyperloop accident will result in the instant death of everyone in the capsule and almost everyone in the entire Hyperloop with the explosive decompression."

The LA trials won't take place in a vacuum but rely on linear motor propulsion and magnetic levitation. That's the reason why the test pods won't exceed speeds of 240 kmh (or 150 mph) - significantly lower than, say, the 1080 kmh (670 mph), targeted by the Hyperloop One team. Such high speeds would give Hyperloop a definitive advantage over high speed trains, such as Japan's bullet trains. "If, however, the top speed was lower at around 350mph, then Hyperloop would be competing directly with high speed trains, which would be difficult if construction and running costs were significantly higher," says Carlo van de Weijer, director of the strategic area Smart Mobility at Eindhoven University of Technology.

Even if vacuum in a Hyperloop system could ever be achieved, a transportation system under vacuum in tubes on pillars might never be totally safe, says Marcel Jufer, a professor at the Swiss Federal Institute of Technology in Lausanne (EPFL). There is risk of sabotage, earthquakes, and difficulties of evacuation. "The underground solution is much safer." Technologically, however, the transition of vehicles from atmospheric pressure zones to vacuum in the tubes (or tunnel) would be a challenge, he adds.

In the early 1980s, Jufer led Swissmetro - a maglev train project at EPFL that evaluated the development of an underground network of tunnels to connect several main Swiss cities. The trains would have travelled at 450 kmh. The project was later dropped, officially because of cost. For Hyperloop, cost - especially that related to supporting infrastructure - may be an equally big obstacle.

Then there is the issue of comfort, and the balance between curvature of the loop versus the comfort of the ride, which is an important challenge, says van de Weijer. "It will be an enormous barf ride," he adds. And capacity will be nowhere near what one would expect from a train connection. These two factors will suffer greatly from increased speed.

But the biggest issue, says van de Weijer, is that it's not quite clear what problem Hyperloop is meant to solve. "To facilitate city to city transport, or city to anywhere else, is nice for rich people that live and work there, or to facilitate having a coffee in Milan when you live in Amsterdam - but that's sheer hipster-satisfaction," he says. At least I haven't seen a decent explanation of why we would need this. It just makes people travel further and more with no real economical and societal justification."

But at the very least, ambitious projects like a Hyperloop transportation system may give "people and especially students a dream to chase," van de Weijer adds. "It will not lead to a new transport system, but they will learn and find many other things on their endeavour that they otherwise would have never learned or found."


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