Elon Musk's 'hyperloop' (a.k.a. 'vactrain') has been all over the news the past several days. http://en.wikipedia.org/wiki/Vactrain http://en.wikipedia.org/wiki/Pneumatic_tube The main problem, as I see it, is the incredibly expensive infrastructure required, not just at its endpoints, but all along the path. I think it would be faster & cheaper to do what I call a 'ballistic hyperloop'. As Crocodile Dundee might have said, "now _that's_ a hyperloop!". Here's the idea: Launch a _ballistic_ projectile from L.A. towards S.F. At the SF end, there is a 'receiver' that is basically a time-reversed launcher. I hope that the following (flat Earth) calculations are correct. It is approximately 560km (348 miles) from LA to SF. If we launch our vehicle from LA to SF at a velocity of 1.97 km/s (4400mph) at a 45 degree elevation, our vehicle will arrive in SF in about 402 seconds (6:42). The vehicle will reach a height of 49.5 km (31 miles). In order to keep the acceleration to within approx 6 g's, we need about 33 seconds of acceleration, during which time we travel about 33km (about 20 miles). 20 miles of infrastructure is too much to put even on a mountain side in L.A., so we have to do better. If we put the passengers into a water-filled container, we might be able to do 12 g's, which would reduce the acceleration distance to perhaps 10 miles, which would be easily doable on Interstate 5 to the north of Los Angeles. A 'normal' landing would require slightly less acceleration in reverse due to the atmospheric losses on launching and landing. An 'abnormal' landing would require a parachute, and would happen if the onboard computers decided that it would be impossible to land safely in the 'receiver'. Here's why it is a 'loop'. At the receiving end (Mt Tam?), the projectile comes in and starts pushing air through a tunnel to the SF-to-LA launcher. This air is 20% oxygen, and it will get very hot, very quickly. We now inject some fuel -- e.g., diesel fuel, liquid natural gas, etc. -- into this air. We carefully select the amount of injected fuel to simply make up for the lasses in the system. The incoming projectile thus transfers its momentum & energy to the outgoing projectile, with enough added energy to make up for the losses, and the SF-to-LA projectile is now on its way. Yes, you get a little wet & have to take a shower when you arrive in SF, but if you are subjected to 12g's for 16.4 secs on launching and 16.4 secs on landing, you'll probably wet yourself anyway. Total time, including showers: 30-45 minutes. _No_ infrastructure required, except at the launching & receiving ends. Forget SpaceX; this will be the real E-ticket ride at Six Flags Magic Mountain (off I5 north of LA). Needless to say, the noise outside will be incredible, both on launching and landing.