More details in this pdf on the hypersonic skyhook The early stage skyhook could be a rotovator that is 900km long or a cardiorotovator that is 1800mk long and has a rendevous speed of 8.7 Mach.
“The energy result would be about 2600 kw•hr, which is a very small energy cost compared with other launch technologies, such as a pneumatic acceleration system,” Yang explained. “Key challenges for this maglev launch assist are the linear motor’s acceleration system and its power supply system, which are required to provide an acceleration of 2g-3g (gravity).”
In their model of a test vehicle on a seven-meter-long track, Yang’s group used a suspension system based on bulk high temperature superconductors, which achieve highly stable levitation due to their diamagnetic and flux pinning properties. The researchers used an arrangement of YBCO bulk superconductors, which achieve their remarkable property of zero resistance at 77 K. When the superconductors were cooled to this temperature, the test vehicle levitated freely over the track.