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Metropolis 2: A unified approach to airspace design and separation management for U-space

Periodic Reporting for period 2 - Metropolis 2 (Metropolis 2: A unified approach to airspace design and separation management for U-space)

Reporting period: 2021-11-01 to 2022-12-31

Metropolis 2 aimed to provide the fundamentals for concrete solutions for U-space U3/U4 services that are needed to enable high-density urban aerial operations, with a unified approach to the following U-space services: strategic deconfliction, tactical deconfliction, and dynamic capacity management. It considered three different separation management concepts, differing in how separation is performed (strategic/tactical, ground/air).

The objectives of the project are formulated as follows:

Objective 1: Extend the segmentation and alignment principles of geovectoring to an operational concept for airspace rules to enable high- capacity urban airspace.

Objective 2: Develop a unified design approach to the management of traffic in high-density urban airspace on all timescales, based on the segmentation and alignment principles of geovectoring, in combination with flight planning and detect and avoid paradigms that are designed to leverage the alignment principles from geovectoring, to define robust and efficient flight plans, as well as safe and compliant resolution strategies, which are suitable for operation in a densely used airspace.

Objective 3: Determine the benefits and drawbacks of separation management paradigms with different approaches to who acts as separator: the drone, the U-space service, or a combination thereof, and different combinations of procedural and tactical separation.

Objective 4: Investigate a priority-based integration of manned aviation in urban (drone-only) airspace that robustly integrates with airspace rules and separation provision, such that safety for manned flight is guaranteed, while minimizing degradation of capacity.

Objective 5: Demonstrate the final concept coming out of the Metropolis 2 project in a real-world demonstration.

With respect to the degree of centralisation, it was seen that having centralised strategic control over all flights, where a joint optimisation is made, did not result in superior performance in terms of safety, compared to reactive, purely tactical separation management, even when no stochastic elements were present in the simulation. This can be seen because the level of intrusions between the two extremes, centralised and decentralised, was similar. However, an improvement in safety seen in constrained airspace for the hybrid concept shows the potential benefit of combining strategic management of traffic (flows) with tactical separation management.
The results of the hybrid concept also reconfirm the safety benefits of an alignment promoting airspace design. In the hybrid concept, the “ring-road” design of open airspace reduced the number of conflicts and intrusions. However, this “ring-road” concept in the hybrid system did tend to add more flight distance and time as compared to the other concepts. This shows that in urban air operations there is an important trade-off between efficiency and safety when considering the airspace structure and strategic routing. Strict pre-planning may have the unintended disadvantage of reducing the accessibility and overall capacity of the airspace.
In the first year, the Metropolis 2 consortium worked on creating three separation management concepts, in three competing teams: A centralised concept, a hybrid concept, and a distributed concept. The aim of the centralised (or ground) concept is to benefit as much as possible from the opportunity to centrally coordinate and optimise flights. The hybrid concept aims to investigate a middle-ground solution between the completely centrally optimised concept on the one hand, and the completely decentralised concept on the other hand. The hybrid concept therefore combines centrally optimised strategic planning, with decentralised tactical separation management. In the decentralised (or airborne) concept, separation management is completely decentralised, operating only on a tactical level. A central agent is still present, though, to perform flow management. The primary difference between these three concepts is the degree of centralisation of the separation management task. Based on the outcome of the comparison of concepts the project aims to answer the question of who should be the separator (a central agent or the individual agents). These concepts will be compared in the second year of the project, in a series of fast-time simulations. The scenarios for these simulations, as well as the metrics to observe their performance, were developed alongside the design phase of the concepts. Preceding this work, a survey of previous U-space projects and relevant literature was performed, to provide input to the concept designs, and scenario and metric definition. The (preliminary) outcome of the concept designs, and the scenario and metric definitions were presented in October, during the first dissemination workshop of the project.

In the second and final year of the project, the three separation management concepts were compared in a series of simulations. The simulations incorporated high traffic densities, different types of airspace (free and constrained), different mission types, and off-nominal events (wind and rogue aircraft). A trade-off based on the simulation results revealed the hybrid concept as the most effective in terms of safety. During the project's second workshop, a series of live demonstrations was held. The objective of the live demonstrations was to showcase each concept, and specifically the selected concept, and how urban air traffic could operate in the future. Therefore, 4 scenarios were prepared that showcased the characteristics of the three concepts. Two additional scenarios were prepared with the goal of showcasing U4 services by communicating with a U-space service provider. This resulted in a successful demonstration of drones successfully coordinating strategically and tactically.
To be able to support the high traffic densities envisioned for urban airspace, the operational concept needs to go beyond the exclusive use of airspace. The outcomes of the first Metropolis project give a strong indication that a ‘lanes’ concept will not provide the greatest safety, efficiency, and capacity benefits. Instead, it showed that a more moderate level of airspace structuring is needed to facilitate safe, high-density operations. Metropolis 2 will build on the results from the first Metropolis project, to provide the first unified approach to airspace design, demand/capacity balancing, flight planning, and separation management.

The introduction of new forms of urban mobility such as drone delivery services and personal aerial mobility are seen as enablers for large improvements in quality of life and economic activity. When successful, advanced U-space services such as the separation principles investigated in Metropolis 2 will enable the safe and efficient operations of large numbers of drones without adversely affecting manned aviation. Metropolis 2 will address this specifically within the urban scope. When successful, the Metropolis 2 project will be able to show the correct way forward to make this possible.
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