Hyperloop

This is a topic that interests me a lot, so I expect this will be the first of many posts.

Elon Musk and team have posted his "Hyperloop Alpha" essay today.  It's not quite what I'd thought (I thought Vactrain) but it's close.   They've done quite a bit more than "envelope" level engineering but it's still very far from something that can actually be built.  There are a lot of appealing concepts, and the most appealing of all is that he's beginning to work out costs and they're surprisingly reasonable--under $8B for the initial SF-LA route.  This compares with $65B for the proposed High Speed Rail with roughly the same service and less than 1/3rd the speed.

It consists of a pair of steel tubes, normally elevated, which are evacuated to 0.015 psi.  This not quite a hard vacuum but "soft" enough that relatively ordinary equipment can be used to maintain it, and some tiny leaks can be tolerated.  This is about the same pressure as a spacecraft flying at about 30 miles would feel.  Pretty low drag, but far from zero, especially at the proposed 760mph, approximately 1/1000th of sea-level drag.  The vehicle is substantially smaller than the tube (roughly 30%) and has on the front a big fan, which sucks in air.  Most of this is spat out the back, helping to keep it going, but a little is squeezed out the bottom through what they call "Skis", which ride on the floor and sides of the tube, generating a cushion of air to ride on.  This is familiar to people who play air hockey, and it's been used in lower speed transit before, such as the people mover in the Detroit Airport.

The low pressure in the tube means that it doesn't take a lot of power to overcome air friction and can be sustained by on board batteries (using numbers gleaned from their work with the Tesla S), and the big power drain from acceleration is accommodated by Linear Induction Motors (many existing transit designs use LIMs, such as the Vancouver Skytrain).  These are mounted in the tube and the vehicle itself is passive.  They are also used to decelerate the vehicle, recovering a large fraction of the energy used.  They propose mounting solar panels on the guideway and calculate that those and a rather minimal amount of battery storage will fully power the thing.

They've actually done quite a bit of engineering on the support columns, concerned (it being proposed for California) about earthquakes.  They allow the tube to shift freely a little bit relative to the support in three axes and have the ability to make more permanent adjustments to accommodate shifting terrain.   The propose most of the route down the center divider of Interstate 5.    They'd first connect LA and San Francisco, and later add extensions to Sacramento, Fresno, San Diego and Las Vegas.  Most of the trip would be at 760mph, handling the curves required by the hilly sections near the ends at 550 and 300 mph, leading to a time en route of 35 minutes.

The vehicle itself is a low tube, with the fan section and associated mechanism at the front, and 14 pairs of very recumbent seats for passengers on either side of a big central longitudinal hump.  The whole thing is less than 5 feet wide.  They would depart every few minutes, unscheduled.

The have a separate design which is big enough to carry cargo, including three cars.  It requires a bigger tube.  They seem mostly to be concentrating on the smaller one.

This seems silly to me.  The size of the vehicle is limiting for a lot of people: elderly and other sorts of low-mobility people will need considerable assistance to get in and out of the seat, and even fully able passengers are trapped there for the duration.  A child requiring assistance will be fairly far from their caregiver.  There's lots of necessary luggage that could easily be accommodated with vehicle that's just a little bigger: wheelchairs, bicycles, etc.  Making it big enough to handle a passenger in a wheelchair will allow people to move around a little, including relieve their bladder, caregivers to help children and disabled, ease entry, and more, while only growing the overall size of the vehicle and structure 20% or so.