# Implementing and Testing a U-Space System: Lessons Learnt
## 6 Discussion
For instance, even if the route of the traffic is not yet affected but a future conflict can be inferred (e.g., a rogue drone). One of the main challenges during the implementation of the UTM was having several services interconnected and events that trigger different actions in various of them that sometimes require a specific order of execution and updates in the data structures of the services. This complexity, despite having implemented only a small part of the expected services, suggests the difficulties that will imply integrating more services and sources of information. A careful design and documentation of the architecture and the sequence of actions to attend to each event from the beginning of the development is fundamental. Another topic to which pay attention will be the resilience of the system to communication fails. In the case of position reports, a reporting gap triggered actions associated to an assumed lost link, which could lead to unnecessary deviations and warnings to the rest of the users even when the problem was just temporal. Instead, the reaction of the system could be adapted to each situation, i.e., increasing the margin of time to trigger such actions depending on the risk associated, or obtaining the support of other tracking sources. During the experiments, the quality of the communications was not a problem, since the flights were realized in flat and empty areas, without obstacles, sources of interference and a good coverage, so no relevant package loss was seen. But we cannot expect the same flying in other conditions, like while overlying a city with more traffic density. However, the streaming of the video from the drone failed several times, which was a problem for the situational awareness but particularly for the drones whose mission depended on the images captured--evaluation of the area with the emergency, or the monitoring of the traffic. This was despite the fact that M300 allowed for the use of a transmission channel dedicated to payload. With respect to the graphic interface, its usability, adaptability and a clear display of the relevant information, will influence the mental workload of the flight crew and how fast the tasks can be performed, which will be important in the case of operating swarms. In this regard, the feedback of users is fundamental. Therefore, a successful development should go hand in hand with operators, pilots and GCS developers, this being the best way to identify needs and constraints at all levels. Conceptualization, methodology, M.-A.F.-M.; software, M.-A.F.-M., A.P., A.P.T. and D.G.d.R. ; validation, D.G.d.R. and R.G.G. ; writing--original draft preparation, M.-A.F.-M.; writing--review and editing, M.-A.F.-M., D.G.d.R. and R.G.G. All authors have read and agreed to the published version of the manuscript. Funding: The Labyrinth project received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 861696. The authors would like to thank for their valuable contributions to this work to: [PERSON], who developed the real-time computer vision-based car speed measurement tool and its Web interface, used in one of the use cases; [PERSON], responsible for the integration of U-Fly (DLR's GCS) and a drone platform, in the U-space environment, necessary for the satcom tests, for which he also had to modify the satcom solution; Atmosphere, the company providing the satcom solution, cooperated by supporting with technical assistance and special access to their resources so that their solution could be adapted to the needs of the drone to connect to the U-space server; [PERSON], responsible for the simulations and analysis of the path planner sub-service; [PERSON], in charge of integrating Arquime's GCS in the U-space environment and performing their flight tests; the Rozas Airborne Research Center (CIAR), providing the infrastructure and support for the real flight tests of part of the use cases; and the Spanish National Geographic Institute for their help to work with their elevation maps.