As promised, this afternoon Elon Musk revealed further details and his thoughts behind “Hyperloop Alpha,” a proposed passenger pod-in-tube transportation system intended as an alternative to high-speed rail, and for than matter, supersonic air transport.
Presently there is no supersonic air transport operating in the U.S., but that outside-of-the-box thinker Musk mentions it as a possibility “short of figuring out real teleportation, which would of course be awesome (someone please do this) … ”
While Star Trek technology has been humbly requested, Musk said the idea he can see as technically feasible – although he may not actually go so far as doing the project himself – was in response to his disappointment over California’s high-speed rail system approved and to cost tens of billions, and in process.
To outline the Hyperloop alternative, Musk offered a 57-page multi-part abstract in both layman speak, and more technical jargon. It may well have errors and omissions he said, and Musk paints it as an open request for constructive feedback from other possibility thinkers like himself.
Premises behind this system are to beat the exorbitant and potentially problematic rail system being pushed forward in the financially struggling state, as Musk says below:
If we are to make a massive investment in a new transportation system, then the return should by rights be equally massive. Compared to the alternatives, it should ideally be:
• Lower cost
• More convenient
• Immune to weather
• Sustainably self-powering
• Resistant to Earthquakes
• Not disruptive to those along the route
According to the California High-Speed Rail Authority:
California high-speed rail will connect the mega-regions of the state, contribute to economic development and a cleaner environment, create jobs and preserve agricultural and protected lands. By 2029, the system will run from San Francisco to the Los Angeles basin in under three hours at speeds capable of over 200 miles per hour. The system will eventually extend to Sacramento and San Diego, totaling 800 miles with up to 24 stations.
A Better Way
Musk says the proposed “fifth mode after planes, trains, cars and boats” which is a new twist on an old idea can be done.
“The Hyperloop (or something similar) is, in my opinion, the right solution for the specific case of high traffic city pairs that are less than about 1500 km or 900 miles apart,” says Musk. “Around that inflection point, I suspect that supersonic air travel ends up being faster and cheaper.”
For distances of less than several hundred miles, a supersonic plane makes no real sense, he said, as maximum air speed is achievable only once it has slowly accelerated and ascended high into thin air and where the sonic boom will not be intrusive to those one the ground below. A supersonic plane must also spend a significant distance and altitude coming down and slowing down as it approaches its destination.
They only make sense for longer distances, Musk said. Previously the Concorde supersonic transport – retired in 2003 after entering service in 1976 – was known as an expedient means to travel from the U.S. to England or Europe as much of the booming craft’s journey was over ocean.
More recently a “Son of Concorde” has also been proposed.
Rather than a pure vacuum for the proposed Hyperloop, which would be problematic at least, Musk says, a partial vacuum in a low-as-possible cost tube would be best for a passenger pod intended to ply its way between cities at several hundreds of mile per hour.
The “Kantrowitz limit” a Hyperloop would need to overcome is the name given for “nature’s top speed law for a given tube to pod area ratio,” Musk says.
“The approach that I believe would overcome the Kantrowitz limit is to mount an electric compressor fan on the nose of the pod that actively transfers high pressure air from the front to the rear of the vessel. This is like having a pump in the head of the syringe actively relieving pressure.”
At the same time, it would allow for comfort in a low-friction suspension system. At speeds of 700 mph and above, “wheels don’t work very well,” Musk benignly says.
On the other hand, like an air hockey table principle taken to the macro level, the cushion of air that could be created does, he says.
To make it feasible, the pod would have a large storage battery on board to keep the fan running all the way from LA to San Francisco or vice versa.
This battery pack however could only supply enough energy to keep an already moving pod up to speed, but not create the initial major power required to get it up to cruising speed.
The capsules would be accelerated via a magnetic linear accelerator affixed at various stations on the low pressure tube with rotors contained in each capsule.
“This is where the external linear electric motor comes in, which is simply a round induction motor (like the one in the Tesla Model S) rolled flat,” says Musk. “This would accelerate the pod to high subsonic velocity and provide a periodic reboost roughly every 70 miles. The linear electric motor is needed for as little as ~1% of the tube length, so is not particularly costly.”
The other advantage the Hyperloop concept has over high-speed rail is feasibility of the route. Musk says the tube could be placed under ground, but actually proposes it follow much of the route of California’s I-5 and be mounted on pylons.
These would be far more resistant to earthquakes and mild resettling of the earth along the route. Farmers could also work around the pylons that create little more footprint that a telephone pole, as opposed to a 100-foot-wide easement striped through the route along with needed security fences.
Musk has also proposed travel all the way from California to New York, but his initial look focuses on starting in his adopted home state.
As mentioned, Musk says the pod could be self powering, and offers a detailed tech section.
However, for those wondering whether this is really possible, “the short answer is that by placing solar panels on top of the tube, the Hyperloop can generate far in excess of the energy needed to operate. This takes into account storing enough energy in battery packs to operate at night and for periods of extended cloudy weather. The energy could also be stored in the form of compressed air that then runs an electric fan in reverse to generate energy, as demonstrated by LightSail.”
To learn more, the entire 57-page explanation is linked here.