Space has been populated by a wide range of satellite systems from governmental and private space entities. Monolithic satellites have been ruling it by providing a custom design that accomplishes a specific mission. Nevertheless, novel user demands emerged have required global coverage, low revisit time, and ubiquitous service. The possibility to integrate in-orbit infrastructure to support current communications systems has been discussed persistently during the last years. Specifically, the concept of deploying networks composed of aircraft and spacecraft (creating the so-called Non-Terrestrial Networks), has emerged as a potential architecture to satisfy this new demand. This novel concept has enabled to investigate mobile technologies in space infrastructure. For example, this is the case of the Software-Defined Satellite, which aims at managing in-orbit infrastructure by using Software-Defined Network techniques. These novel concepts pose multiple challenges which dedicated developments shall address. Likewise, specific equipment and simulation environments shall support them. Currently, open source satellite network emulators have certain limitations or are not easily accessible. This project aims at presenting the Virtual Satellite Network Simulator, a novel simulation engine capable to represent satellites as well as ground nodes in virtual machines and deploy a virtual network that depicts the channel effects and dynamics. VSNeS has been generated from different modules, that thanks to the joint work is able to generate the virtualization. First of all, a Python3 program has been developed, which works as a manager and is responsible for running the rest of the modules according to the virtualized scenario. Furthermore, Kernel-based Virtual Machine has been implemented for the execution of the virtual machines. The channel management is done with the NetEm emulator. Finally, a graphical user interface is delivered by Cesium. This dissertation presents formally a preliminary design with the essential steps to select each technology. Then, the networking design is also discussed. Different tests are also shown in order to verify the correct functioning of the tool. In addition, tests about the performance of the final release have been performed. The program has been tested with the following protocols in different realistic scenarios: TCP, UDP, and ICMP. This allowed us to verify the correct operation of the program, checking the delays and channel losses. Moreover, it is empirically demonstrated that some protocols are not functional for geostationary satellites, due to the long latency caused by the large distances
