Vactrains are an extremely sophisticated (and highly experimental) magnetic levitation technology that moves a vehicle along a magnetic rail just like Maglev, but instead of operating inside an atmosphere, the train operates inside a vacuum or low pressure tube. Despite its highly experimental nature, the technology shows a great deal of promise and has attracted many supporters in recent years. Sometimes called evacuated tube transport, the effect of moving a Maglev system in a vacuum (or near vacuum) is that immense speeds will be possible. Little to no air resistance will completely eliminate air friction, the main speed inhibitor for trains. ETT transport systems would be capable of propelling trains from 4,000-5,000 mph (6400-8000 km/h) an astonishing speed. For reference, that is 5-6 times the speed of sound at sea level. The way ETT is supposed to work is air is permanently evacuated with pumps from the tunnel running the route. Passenger and cargo capsules travel along via frictionless Maglev. Airlocks at docking stations would allow passengers and cargo to be debarked without letting air inside. After each boost of propulsion from the linear accelerators the capsules travel without any additional energy. Acceleration energy is recovered by using the same linear accelerators to decelerate the capsules. Lack of air resistance or rolling friction means ETT is potentially able to be 50 times more efficient per kilo-watt hour than electric cars or trains. Proposed EET capsules weigh only 400lbs yet can carry up to twice that. Only a fraction of the amount of materials is needed to support EET capsules than traditional rail locomotives. Savings in materials as well as the potential for automated tube manufacturing makes costs only a fraction of traditional high speed rails or automobile highways.
The ultimate goal for super-speed tube trains (SSTT’s) is to be competitive with air travel. Current ground-level Maglev trains can reach speeds up to 360 km/hr making them competitive with all existing high speed train technologies. However, at distances greater than 800 km air travel is still superior. The Japanese have been working on a ground-level Maglev train capable of an estimated 500 km/hr which would only marginally help close the gap between air and rail travel. The immense amount of capital and money required for initial investment however make the technology far from viable. If rail transport (Maglev) is going to be completive against air travel much greater speeds will be necessary.
There are two options for Vactrains: subsonic speeds in partially evacuated tubes or the equivalent of supersonic speeds in near total vacuum tubes. In order to achieve SSTT numerous technical problems must first be solved. For example, careful planning is required when building SSTT infrastructure due to the inherently instable nature of traveling at such great speeds on a mag-rail. At a speed of 900 km/hr (250 meters a second!) for instance, the minimal turning radius must be 25km assuming an acceleration of 2.5 m/s^2. This alone means that building an actual nationwide Vactrain network might be impossible due to existing underground infrastructure (water, electrical, gas, etc.) as well as private ownership of land necessitating the use of imminent domain (a quick way to lose public support for a project). If speeds are to approach ½ the speed of sound, 340 m/s, then partial atmospheric evacuation is required to maintain reasonable energy efficiency. This would require the technology to build, design and maintain the low atmospheric tubes to be affordable and for the science and engineering behind everything to be well understood and tested. The best propulsion system for a subsonic SSTT would be a Linear Synchronous Motor paired with an Electro Dynamic Suspension system used by the Japanese on their high speed trains. These are suitable options because the technology has already been thoroughly tested,
