I think it's safe to say Elon has officially lost his mind. It's sad, but it happens frequently to people with too much money.<p>No one person can fix electric cars, solar power, underground urban transportation, and sending people into space. No one. The flying Tesla is only slightly more kooky than the one-at-a-time Tesla going through his tunnels. Britain had electric underground railways in the 1800's. I fail to see how Elon's tunnel invention is improving on that.<p>People can't go to Mars because of the Van Allen belts. But Elon wants us to get excited about 50's-style stainless steel rockets. Come on.
He replied that it's just some high pressure air cylinders and thrusters. Same composite overwrap tank technology that are in a Falcon 9 helium tanks.<p>You could probably add water to make the thrust higher, to make a bottle rocket...