## 4 Discussion  
A high-speed transportation system (Hyperloop) for freight transport has been pre-designed in this work. As seen in Figure 6, it has been found that the most effective configuration is a vehicle with 5 containers moving at 750 km/h in a 750-km tube. This vehicle is capable of delivering 141 t/h with a consumption of 2.27 \(\times\) 10\({}^{-2}\) kWh/tkm. However, it is necessary to review certain aspects found when analyzing the predesign (the values from Table 3):  
* \(D_{t}\) measures 9.37 m and is too large because this vehicle lacks an instrument (such as a compressor) to bypass the incoming air. This also impacts speed, since a high-speed transportation system equipped with a compressor is able to reach higher speeds. This last case, in which the vehicle levitated on air bearings instead of magnets, was studied in [24] as an alternative and it was found that this type of vehicle cannot transport a huge amount of freight because maximum mass flow through the compressor limits pressure under the air bearings and, therefore, payload. Nonetheless, a high-speed transportation system with a compressor levitating on magnets has not yet been studied and is proposed for further works. Moreover, it should also be studied whether, or not, it is feasible to build a 9-m diameter tube. * It should be determined if it is feasible to build a 750 km long EDS or if it would be preferrable to build only some sections of it (the vehicle would cruise between those sections, as proposed by [17]). * At the ends, near the cargo terminals (at the acceleration and deceleration lengths), this EDS system should be able to withstand 720 MW (\(P_{1}\) in Table 3) and evacuate the generated heat (194.40 MW, 27%, because 1 \(-\eta_{EDS}=0.27\)). State-of-the-art EDS systems are not likely to withstand such an enormous power. In this case, the first approximation done in this work should be discarded and acceleration reduced. If, for instance, 2.10 m/s\({}^{2}\) (1/7 of 14.72) were to be used, its power would be 103 MW, a result which nears the result of reference [17]: 50 MW is the traction power for his first model [17] and for his second model it is 87 MW. The mean speed would barely be affected, as it would only be reduced from 747 to 730 km/h. This can be previewed on the next plot (Figure 7), although the optimization of acceleration and EDS power should be deeply studied, so they are two topics proposed for further studies:
* In addition to the optimization of EDS power, the pole pitch should be adjusted to have \(C_{D_{EDS}}=3\times 10^{-3}\) or even lower. Thanks to such a good coefficient \(F_{D_{EDS}}\) is only
5 kN (very low in comparison with \(F_{z}\), which is greater than 1.5 MN), and this drag force can further be lowered, as is shown in Figure 8:  
* An attempt to lower \(m^{\prime}_{est}\), which is the main dead weight of the vehicle, could also be carried out. Nowadays, there are many composite materials reinforced with advanced fibers (carbon-graphite, aramid, etc.) and alloys (aluminum alloys, for instance) which could lighten the vehicle while resisting the stresses and forces generated. If the structure weight could be lowered by 50%, then the energy index could be cut by 3.88% (Figure 9a), and the energy saving could be further augmented to 4.59% by cutting the rest of dead weight (namely, \(m^{\prime}_{EDS}\) and \(m_{EB}\)) in half also (Figure 9b):  
* With respect to the Kantrowitz limit, the vehicle is meant to run at 750 km/h in a 9.37-m diameter tube and at 20 \({}^{\circ}\)C. At 30 \({}^{\circ}\)C, speed could be slightly raised and at 10 \({}^{\circ}\)C speed should be slightly diminished to avoid the air stacking. These possible slight variations are illustrated in Figure 10:  
Figure 8: Correlation between \(C_{D,\,EDS}\) and \(F_{D,EDS}\), the latter 5 kN at \(C_{D_{EDS}}=3\times 10^{-3}\).