Satellite antenna size and the data throughput achievable in a satellite communications channel are directly related, but the benefits from an increased aperture size can also be used to enable access to smaller ground antennas or to improve QoS, as well as increase data throughput. As well as gain, increasing satellite antenna size also enables increased spatial discrimination, enabling greater frequency reuse across a given service area. With the satellite industry's shift from a broadcast model to a connectivity-based approach comes increased competition with terrestrial networks, and a corresponding need to increase total system throughput and spectrum utilisation. The result has been greater interest in larger antenna systems for telecommunications missions. Whilst increasingantenna aperture size will always result in a corresponding increase in link performance, if a significant step forward could be made, a tipping point might be reached allowing direct broadband access to hand-held devices from orbit. Such a step change would have a significant impact on the addressable market and range of applications that could be supported by the satcom sector. Solid shell reflector antennas, limited in size by the stowable dimensions within a launch vehicle fairing (approximately 2 to 2.5 m in diameter), have been the mainstay of communications satellites for many years now. Larger deployable mesh reflector antenna products (of between 9 and 12 m diameter) were first developed by US manufacturers and successfully used in orbit over a decade ago. More recently, systems have been deployed in orbit of up to 18 m in diameter from both the US and China. These products serve the MSS market however, and therefore operate at relatively low frequencies (2 GHz and below), but in more recent years, reflectors of up to 5 m in diameter operating at higher frequencies (up to 30 GHz) and have been successfully deployed. Despite many individual design and technology development activities, a comparable commercial product has not yet reached the market from a manufacturer based in the ARTES participating states. This is likely a consequence of the limited commercial demand for such products in current mission architectures, rather than as a result of unsurmountable technical challenges. (See activity report for Large Aperture Antennas and Associated Reflector Requirements, 1B.075). The development of a 7.5 m diameter reflector operating at above 30 GHz is however now underway in Europe as part of a future Copernicus mission. The engineering challenges of releasing large reflectors in orbit, e.g. surface accuracy,stability, and reflectivity, their impact on overall spacecraft pointing accuracy, deployment reliability, and stowed dimensions, etc. does however place practical boundaries on the continued upscaling of such systems. Significant growth in antenna size beyond that targeted by current reflector developments seems unlikely without a fundamental change of approach. The concept of realising large antenna apertures in orbit by employing array techniques has been understood for some time now, but recent advances in in-orbit manufacturing and assembly technology, as well as improved production techniques for small low cost spacecraft, mean that such an approach could well become technologically and commercially feasible in the near term. The proposed activity would therefore comprise aninvestigation into techniques and topologies for realising very large array antennas in orbit. The survey should consider in-orbit assembly of pre-manufactured modules, the technical feasibility of solutions combining "formation flying" of unconnected orbital elements (i.e. fractionated antennas), or any other approaches that may allow to realise the same objective. Consideration should begiven to radiative element design, sub-array definition, beamforming, power and low noise amplification, D.C. power generation and distribution, data Connections/transmission between elements, scalability, and reliability. Whilst the investigations should consider feasibility in all frequency bands currently used for satellite communications, (i.e. from VHF to Ka-Band), as well as bands likely tobe brought in to use in the future (e.g. Q, V, and W-Bands), effort should be focused on higher frequencies where greater bandwidthis available. Whilst there is little verifiable information in the public domain, it is understood that there are ongoing developments in both the US and China aimed at producing unfurlable antenna reflectors of around 20m diameter that support operation at Ka-Band. The activity should therefore target array solutions of an order of magnitude greater than traditional solid-shell reflector solutions, i.e. over 20m in diameter. Having identified the most promising approach, a more detailed feasibility assessment shall be performed, defining achievable performance targets, simulating link level performance, and providing power, mass, and cost assessments. The outcome should be a technology development roadmap defining the development steps and timescales needed to realise new satcom systems based on the identified approach (if shown to be feasible). Both developments highlight the erosion of barriers around the commercial satcom industry and a movement away from thinking the challenges faced by the satcom sector are in some way special or unique. Many other high-tech sectors (Medical, Aviation, Military, Automotive, Transportation, Terrestrial Communications, etc.) have to meet high performance requirements in challenging environments and there is therefore much that can be learned from these industries. There are many current examples of space sector innovation that results from leveraging capabilities developed in other industries: wireless passive on-board sensors for spacecraft (limiting harness complexity), applying terrestrial M2M protocols (e.g. LoRa) to LEO space systems, Relativity Space making extensive use of additive manufacturing techniques to reduce part count and cost of their Terran 1 vehicle, etc. As well as technology transfer, alternative business models have also been successfully replicated betweensectors; e.g. meeting needs through a service offer as opposed to ownership, with Philips providing light as a service LaaS, havingobvious parallels with Amazon Web Service's Ground Segment as a service in the Earth Observation field. The proposed activity wouldtherefore take the form of a series of systematic surveys of adjacent high technology sectors, and seek to identify techniques, technologies, working practices, and solutions that could be applied within the satcom sector. The activity is likely best realised with established actors from the satcom sector (with a knowledge of current technologies, systems, and capabilities) working alongside specialist groups from other industrial sectors, and so a number of small individual surveys may be commissioned. The primary goal of the activity would be the identification of follow-on technology developments (and ultimately product developments) through the ARTES Core Competitiveness line, or new system concepts for investigation and possible demonstration through Partnership Projects.

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