Objective: The objective of the activity is to develop and test a system simulator testbed capable of modelling and assessing the performance of communication satellite constellations operating in Very Low Earth Orbit (VLEO). This includes the assessment of the emerging waveforms (5G NTN, European Protected Waveform).Targeted Improvements: Enable the design and assess the constellation system performance of communication satellites operating in VLEO. Description: Very Low Earth Orbit (VLEO) satellites, operating at altitudes below 300km, offer several communication benefits such as: 1) Improved link budgets enabling new applications (e.g. direct to handheld communications), where the lower distance between satellite and ground implies a lower power requirement on board the satellite; 2) Higher coverage granularity: The closer distance to ground leads to smaller beam footprints for a given antenna size, improving the possibility of reusing spectrum and increasing the overall flexibility and capacity of the system; 3) Use of COTS components: VLEO satellites are subject to a milder radiation environment and enable tight components integration due to the reduced power requirements; 4) Lower Latency: VLEO satellites are positioned closer to the earth's surface than traditional LEO satellites, which results in lower latency communications. However, the use of orbits below 300km introduces new challenges in the satellite systems design, including: Higher Doppler effects Shorter pass-times, leading to frequent handovers between satellites.Very high number of satellites to achieve global coverage, increasing the complexity of the interconnections and resource allocation of constellations Unlike conventional LEO constellations, the performance of VLEO has not been thoroughly assessed, especially for what concerns the use of 5G NR waveform. The 5G Air interface is desirable for VLEO systems because it leads to lower power and lower latency, which arecrucial for seamlessly integrating the space segment with the terrestrial cellular network. A system simulator will be developed that can model large number of VLEO satellites and is able to evaluate their performance at a system level. This tool would also support the definition of high-level requirements for VLEO payloads in terms of antenna size and required RF power, as well as the development of customised communication payloads within ESA Member States.

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