The billionaire inventor, investor and futurist Elon Musk is set to unveil his detailed proposals for a 4,000mph 'mega train' known as the Hyperloop to connect the east and west coast of the United States.

Musk is the co-founder and CEO of electric car makers Tesla, as well as the private space company SpaceX.

But while you might think a man with two companies, five children and dreams of founding his own colony on Mars might be busy enough, with a networth estimated at around $2.7 billion it turns out he can still find the time, and money, to look for new problems to solve.

This time his idea is based on a principle that's been around for more than a 100 years - a functional, large-scale pneumatic tube train which could propel passengers underground at unimaginably fast speeds.

The Hyperloop was described by Musk earlier this year as "a cross between a Concorde, a railgun and an air hockey table", and would be both relatively low energy and safe, since the system would be totally self-contained.

While such a system would be beautiful to behold - and capable of sending passengers to LA from New York in 45 minutes - it would also be hugely expensive.

But Musk points out that given the extravagant cost of California's already-underway $70 billion 'high speed' rail system - which will be the slowest on the planet when finished - the US can afford to think more creatively about its transport problems.

"What you want is something that never crashes, that's at least twice as fast as a plane, that's solar powered and that leaves right when you arrive, so there is no waiting for a specific departure time," he said previously when asked about the system.

At least one company is already working on a similar idea, and so it's unclear where Musk fits into the scheme. But he now says that he will publish his designs on August 12, as an 'open source' resource to anyone who wants to get involved.

We'll have to wait until then to see what he's come up with. But knowing Musk's work, it will probably turn out to be more insane - and more realistic - than you can reasonably imagine.

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