Hyperloop UPV
The Hyperloop UPV concept is a levitating rail-free pod design. Using magnetic repulsion and air cushioning for levitation is expensive and can produce unpredictable forces. The pod is equipped with a hybrid system of permanent magnets and electromagnet units, being able to control lift, so it can hover from the top of the tube. That way, the pod doesn't need so much electricity to be lifted by itself. Propulsion is obtained through expansion of the air with a nozzle, located at the rear of the pod, achieving speeds of up to 1000 km/h. The turbine recovers energy from the flow allowing a more efficient journey. This clean tube layout is said to cut costs in up to 30% of the whole Hyperloop project (about 180m USD) and the possibility to comfortably fit more passengers.
Hyperloop
In January 2015, a paper based on the NASA OpenMDAO open-source model reiterated the need for a larger diameter tube and a reduced cruise speed closer to Mach 0.85. It recommended removing on-board heat exchangers based on thermal models of the interactions between the compressor cycle, tube, and ambient environment. The compression cycle would only contribute 5% of the heat added to the tube, with 95% of the heat attributed to radiation and convection into the tube. The weight and volume penalty of on-board heat exchangers would not be worth the minor benefit, and regardless the steady-state temperature in the tube would only reach above ambient temperature.