# Case Study of an Integrated Design and Technical Concept for a Scalable Hyperloop System
## 4 Functional Definition
### Propulsion  
To accelerate a vehicle to \(600\,\frac{\mathrm{km}}{\mathrm{h}}\), a special kind of linear motor is required. A short stator linear induction motor (LIM) is commonly used for low-speed maglev systems [13] but loses efficiency substantially at higher speeds due to end effects [22].  
In addition to high speeds, high accelerations are also beneficial because the acceleration directly influences the required length of the on/off ramp to and the length required from the main lane. This is not a problem for point-to-point connections, but it has a large cost influence as soon as more than two stops are connected. This requirement is problematic for the Transrapid drivetrain, where a synchronous long stator uses the onboard levitation system as excitation. With this configuration, achieving accelerations greater than \(1\,\frac{\mathrm{m}}{\mathrm{s}^{2}}\) is challenging because of the coupling of levitation and propulsion.  
Here, an air cored linear synchronous motor (LSM) long stator or a LIM long stator come into place, enabling the demanded \(2\,\frac{\mathrm{m}}{\mathrm{s}^{2}}\). While the LSM needs a strong excitation from either a permanent magnet array or a superconductor on board, there is no expensive lamination in the track necessary. The LIM long stator requires lamination but enables an adaption of the pole pitch and could theoretically even work with fixed frequencies for each track segment. Also, no heavy equipment is required on-board. A simple copper plate or bulk superconductors could be appropriate counterparts. What all of these solutions have in common is the long stator, meaning that the active part of the motor is in the track. Compared to a short stator, this reduces the flexibility during operation and increases the infrastructure costs. Additionally, a short stator is better in facilitating improvements with every pod iteration. But, it must be emphasized that a short stator propulsion instead of a long stator complicates the power supply, pod cooling, and the mass budget drastically.  
Nevertheless, research [23] shows that a linear synchronous reluctance motor (synRM) is a plausible solution for a short stator with a maximum velocity of \(600\,\frac{\mathrm{km}}{\mathrm{h}}\) and a maximum acceleration of \(2\,\frac{\mathrm{m}}{\mathrm{s}^{2}}\). A major disadvantage of reluctance motors are force ripples, which have to be tackled with clever configurations and controlling algorithms. This configuration therefore seems to best fit the requirements to solve the power supply and cooling issues detailed in Sections 4.5 and 4.6.  
For a long stator design, power supply and cooling are not as critical. One sensible consideration is therefore the use of a long stator LIM in booster sections and the use of a smaller-dimensioned short stator for low-speed alignment and maintaining speed. Still,a substantial part of the track would have to facilitate boosters; therefore, if possible, the \"all-in-one\" short stator is preferable.  
Table 4 presents the calculated propulsion requirements. Key inputs include values for aerodynamic drag and drag from the levitation system. The aerodynamic drag values are derived from a transient 2D axisymmetric simulation for a 10 mbar environment at 10 \({}^{\circ}\)C and are in accordance with the findings of [PERSON] et al. [24]. An additional safety factor of 1.85 is included to reflect the 2D simplification [2]. In Section 5.1 the simulated values of blockage ratio (BR), will be utilized. The drag estimation for the levitation system is based on Sinha [20] for laminated homopolar EMS. These values are used to calculate the average energy demand. The maximum motor power required during acceleration is set at 3 MW.