A comparison of vacuum interface options.

This article gives a brief summary of the report on the airlocks at hyperloop stations written by Delft Hyperloop. For the full report, click the button below!


The hyperloop pod travels in a near-vacuum environment. A system should be developed to allow the passengers of the hyperloop system to embark and disembark safely without experiencing the pressure difference. This interface between the low-pressure and atmospheric pressure environments should be designed for safe, efficient, and sustainable operability. In this report, the most promising design options are explained, and a comparison is made. It presents and compares three options:

Bridge Doors

The first option considered is the bridge door, shown in Figure 1. At each platform, when a pod arrives, bridge doors extend from the platform to the pod and lock onto the pod. The bridge is then pressurized, and the doors are opened to link the inside of the pod to the station environment. When all passengers have embarked, the pod doors and bridge doors close and the bridge is depressurized, so the pod can disconnect. Using this method, the pod stays in the vacuum environment while the volume to be pressurized and depressurized can be minimized, which influences the docking and undocking time of the pod and the energy consumption of the system.

Figure 1: Simplified top-view of the bridge doors at the station

The bridge connects to the pod and creates an airtight connection using hooks and seals (Figure 2) inspired by the space station’s docking system. When the bridge is pressurized to atmospheric pressure, the pod’s doors and the bridge doors open, allowing the passengers to enter or exit.

Figure 2: Hard capture hooks

Airlock Chamber

The airlock chamber is a transition chamber between different pressure environments. The pressure in this chamber can vary according to the direction in which the pod is going, whether leaving from or arriving at the station. The chamber is equipped with hermetic doors on each side. If the pod is arriving at the station, the chamber is at near-vacuum pressure so the pod can enter. The door is then sealed, and the chamber is pressurized to atmospheric pressure, so the pod can enter the station. This process is reversed when a pod leaves the station. When the pressure in the chamber and the next environment are equalized, the door separating them opens, allowing the pod to proceed. The chamber is large enough to fit the 30.5 meters pod, hence this structure takes considerable space in the station infrastructure. The simplified layout of the station and the system is presented in Figure ‎3.

Figure ‎3: Simplified top-view of the airlock chamber at the station

End-door Airlock

The third option was proposed by Richard Macfarlane in 2015. It considers that passengers board and alight from the rear end of the pod. Effectively, the interior of the pod becomes linked to the atmosphere at the station when the end of the pod reaches the end of the vacuum tube. In this system, the tube is closed using a hermetic door. When the pod arrives, a section of the pod’s structure opens in an extension of the tube, while the door of the pod remains closed. The pod is then stabilized using hooks to the end of the tube.  Finally, the hermetic door of the tube and the door of the pod open to let the passengers alight or board (Macfarlane, 2015).  The simplified layout of the station and the system is presented in Figure ‎4. The third option presents major complexities, which is why Delft Hyperloop does not consider the end-door airlock feasible for passenger transport.

Figure ‎4: Simplified top-view of the end-door airlock at the station

Comparative Summary

The remaining two options are compared in terms of costs, time, resilience, and safety. The comparative costs are estimated based on required materials, and system components. It is concluded that the bridge doors require significantly higher investment costs than the airlock chambers. However, the bridge doors system is more time-efficient with an estimated operation time of 15 seconds compared to 41.5 seconds of the airlock chamber system which has a large impact on the effectiveness of the hyperloop system as well as the operating costs.

Although the airlock chambers have a lower cost, higher perceived safety, and more freedom, the bridge doors present a major advantage with the low operation time and the limited station space needed. Especially the difference in operation time is significant within the hyperloop system and will save costs in the long run. The significant costs for the bridge door system are outweighed by the large travel time savings. The objective safety levels are comparable due to the high standards set in both cases. The perceived safety can be a concern in the early years of the hyperloop operation, but passengers will get accustomed to the system with more usage. All the aspects are compared in Table 1. Both the airlock chamber system and the bridge door system are feasible solutions for the hyperloop passenger infrastructure. Although Delft Hyperloop proposes the bridge doors as the most viable option for the future, due to the time that is saved, the airlock chambers offer valuable benefits. In the future, a hybrid solution might be utilized that offers the time efficiency of the bridge door system during normal operation, while additional airlock chambers are present to offer resilience in case of emergency, scheduled maintenance or other disruptions.

Table 1: Comparative summary between airlock chamber and bridge doors

Authors: Puck Gerritse and Stavros Xanthopoulos


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