370 Ë 10 HTS Maglev launch technology
A mechanical slide type can be made of smooth metal or composite materials to re-
duce the friction coefficient, but mechanical friction cannot be eliminated absolutely,
so it is not suitable for very-high-speed launch.
The EMS-type Maglev could acquire a stable suspension under the precise active
control of the magnetic forces between the electromagnetic magnet and the ferroma-
gnetic alloy suspended object. The response time of electronic power devices and the
feedback control system is the main problem for the application of EMS type in the
launch system with very high speed.
Because of the stable levitation ability without active control, the HTS Maglev
type is an ideal candidate for a high-speed electromagnetic launch system. Another
advantage of the HTS Maglev type is the self-recovery ability, which means the
HTS Maglev system could redress the minor deviation caused by a disturbance or
oscillation automatically. Compared with rail gun mode or coil gun mode, the linear
motor mode is more suitable for the application of a HTS Maglev system.
10.2 Repeatable electromagnetic launch system
The most important application of HTS Maglev system combined with a linear motor
is the repeatable electromagnetic launch (REL) system of aircrafts and spacecrafts.
The report of the Air Force Office of Science Research (AFOSR) of the USA indicates
that the launch cost of REL system is about 600 USD/kg, which is much cheaper
than the 2000 USD/kg on the space shuttle [3]. The National Aeronautics and Space
Administration (NASA) of the USA has funded several research programs of REL
technology, and they believe the REL has the most potential for the near-earth orbit
launch, over the next 20–30 years [4].
Under the sponsorship of NASA, Jayawant designed a REL system based on an
induction linear motor and an EMS support system [5]. This REL system was designed
to boost the launch in the initial 10–20 s, which could reduce the fuel of spacecraft
dramatically. The research of Jayawant indicated that the EMS support system had
drastic vibration, small force density, and stiffness; in other words, the EMS support
system was not suitable for the REL launch of heavy-load spacecraft [5].
Schultz designed a new EMS support system for REL with support from NASA.
This new EMS support system used LTS coils in place of copper wires, which could
support a spacecraft weighing 590 t. Combined with a linear motor, this REL system
could propel the spacecraft to 268 m/s, with an acceleration of 2g[6].
Those REL systems were primarily designed as a launch auxiliary for the initial
stage. Based on the design of the launch auxiliary system, a comprehensive REL
launch scheme was proposed. To reduce the cost of linear motor, the REL launch
scheme was usually designed to a circular or racetrack shape. The spacecraft accelera-
ted circularly in the REL system to the required muzzle velocity, and then was released
by the REL system with a specially designed switching device. Tidman completed the