A feasibility study for a satellite VHF Data Exchange System (VDES)

University essay from KTH/Rymdteknik

Abstract: Transportation across the globe's oceans increases every year and is expected to keep increasing in the following decades. Consequently, there is a need to establish communication over the horizon through the Automatic Identification System (AIS) and the Very High Frequency (VHF) Data Exchange System (VDES), still in development, to track and communicate with vessels all over the globe regardless of the distance from shore. In this Master thesis a feasibility study for the development of a system that fulfils that need is proposed consisting of a Low Earth Orbit (LEO) constellation providing VDES communication continuously all over the globe. A system engineering approach has been followed, identifying stakeholders and producing system requirements setting up a framework for the system. The key stakeholders were found to be the customers/users, the satellite provider, the satellite operator, the service provider and the payload provider. Furthermore, possible use-cases were presented and a system architecture was defined to outline the system, dividing the system into three segments: the space segment, the ground segment and the launch segment. In addition, design proposals for a satellite constellation and a typical satellite in such a constellation were implemented. The satellite constellation was proposed to consist of 91 satellites at an orbit altitude of around 550 km in polar orbits of common inclination, this was regarding a minimum elevation angle of 10 degrees. The satellite is recommended to consist of a 6 U CubeSat using as payload the existing airborne transponder R5A from Saab TransponderTech, it builds on the Software Defined Radio (SDR) technology and is to be further developed for VDES applications. Moreover, a link- and a data budget were implemented. Different launch options were addressed concluding that launching as secondary payload on a ride-share mission or as primary payload on a small satellite launch vehicle are the preferable options. A market analysis has been made providing details on how many AIS/VDES satellites that have been launched into LEO and by which service provider, as well as further details on small/nano satellites of extra interest to this work. A short risk evaluation was also done, identifying the most evident risks with developing, operating and disposing the system. In addition, Saab's potential role in the development of satellite VDES is discussed.  In conclusion to this work it has been shown that it is possible to build a global continuous satellite constellation in LEO utilising as payload an SDR-platform to provide VDES services to vessels at open seas.

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