European Space Agency (ESA) has been implementing, since 2019, the HydRON (High-thRoughput Optical Network) Project within the ESA ScyLight Strategic Programme Line. HydRON aims to build a network of high-capacity optical inter-satellite links and ground-satellite links that interconnect space assets with each other and with ground networks, and that seamlessly extends the terrestrial optical transport networks into space. Data repatriation from satellite and airborne users, feeder link communications to telecommunication satellite operators, high-capacity connectivity to remote private networks, and dynamic peering to terrestrial network operators are four high-level services that may be provided by HydRON. This paper presents the outcomes of the HydRON Vision Phase-A studies led by Airbus Defense and Space (Germany) and Thales Alenia Space (Italy), completed in 2021. These HydRON Vision Phase-A studies aimed at investigating end-to-end system architectures, and identify key elements of the system architecture such as optical ground-satellite links, high data rate WDMs for optical inter-satellite links, on-board switching and routing in optical and/or electrical domains, seamless integration into terrestrial networks, and control and management protocols. The results of the HydRON Vision from those Phase-A studies described in this paper provided the basis for the definition of the HydRON Demonstration System in the currently running Phase-A/B1 studies, which focus on the in-orbit demonstration of a subset of the key technological elements and the validation of the most relevant operational concepts.
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HydRON (High thRoughput Optical Network) is a project of the European Space Agency (ESA) initiated in 2019. HydRON ambitions to extend high-capacity terrestrial networks into space, seamlessly and by interconnecting all kind of space assets across different orbits and terrestrial networks (i.e., 3-dimensional optical network). The targeted capacity performance is orders of magnitude greater compared to today’s satcom systems (terabit/sec in contrast to gigabit/sec). This paper will present an overview of the HydRON-DS concept, including a summary of the technical baseline and associated programmatics submitted for approval at the ESA Ministerial Council in 2022.
The ambition of the High thRoughput Optical Network (HydRON) project of European Space Agency (ESA) is to seamlessly extend terrestrial high-capacity networks into space. The concept aims to empower satellite networks by developing terrestrial networking capabilities and features, in order to interconnect all types of space assets by an “Internet backbone beyond the cloud(s)”. Concretely, HydRON will take advantage of space assets to complement terrestrial high-capacity networks, ultimately enabling the configuration of a worldwide and world-first 3-dimensional optical network interconnecting terrestrial networks with different (orbital) layers in GEO, MEO, LEO, and HAPS. The 3-dimensional optical network capabilities will revolutionize the SatCom sector and its related commercial business. The HydRON project proposal and initial funding were approved at the occasion of the ESA Ministerial Council in November 2019. To prove crucial aspects of HydRON, a subset of key elements of the overall HydRON System (HydRON-S, encompassing the full width of the future implementation) were selected for implementation in the frame of a demonstration system (HydRON-DS), capable to validate all HydRON aspects end-to-end. HydRON-DS represents the initial stage serving the purpose to gradually demonstrate key technologies required to deploy a first (all) optical transport network at terabit-per-second capacity in space and the seamless extension of terrestrial fibre-based networks into space. The HydRON overall architecture is meant to evolve and enable both architecture upscaling and service expansion.
Free space optics (FSO) is considered a promising technology for satellite communications due to its various advantages over radio-frequency (RF) systems, such as higher throughput, lower energy consumption and smaller mass. Nevertheless, optical satellite communication systems are heavily affected by atmospheric impairments, mainly by clouds. In order to cope with cloud coverage, site diversity technique is employed at the expense of installing extra optical ground stations (OGSs). As a consequence, the interest in ground network optimization is rapidly increasing with the aim to guarantee a given service availability. In this paper, a low-complexity optimization algorithm for ground network design in optical geostationary (GEO) satellite systems is presented, taking into account the spatial correlation between sites. Specifically, the objective is to choose a group of candidate OGSs that minimizes the overall cost of the ground network and meets certain availability requirements for every time period (thus incorporating the temporal variability of cloud coverage). Moreover, an extension of the methodology to optical medium-Earth-orbit (MEO) satellite systems is provided. Lastly, the performance of the proposed algorithm is evaluated via numerical experiments.
The paper investigates the benefits of employing a Variable Data Rate (VDR) scheme in optical Low Earth Orbit (LEO) Direct-to-Earth (DTE) links at system level. In contrast to the Constant Data Rate (CDR) transmission approach adopted in current systems of the kind, the VDR scheme allows to optimize the data rate of the optical link within a satellite pass. Indeed, both the link budget and the atmospheric effects heavily depend on the satellite elevation angle, which varies significantly within a satellite pass. In order to thoroughly carry out the system level comparison between VDR and CDR, the paper first addresses all necessary aspects involved, including channel modeling, waveform and interleaver dimensioning, and link budget issues. For the scenario evaluated in the paper, the average throughput improvement of VDR versus CDR is found to be 100%. The paper also addresses interesting trade-offs concerning possible concepts of operations (ConOps) of the link once the VDR is in place. This preliminary work will be followed up by the Agency with further industrialized technology developments and system refinements.
The paper deals with an analysis of Very High Throughput Satellite (VHTS) systems employing optical feeder links. As the capacities of newly announced next generation VHTS systems are exceeding the Terabit/s barrier, a large amount of investment needs to be directed not only to the space segment (as was the case traditionally), but also to the ground segment in support of the feeder links. To reduce this investment, satellite operators are reviewing various options and technologies for the feeder links, among which optical feeder links [1]. In this paper, different approaches are analysed for ground segment networks relying on Optical Ground Stations (OGS), exploring the concept of smart gateway diversity with N active OGS and P redundant ones, like is currently done in VHTS systems with RF feeder links. OGS locations are assessed in terms of aggregate availability and total cost for the satellite operator, which is an essential element for the viability of the VHTS system. Different options are assessed for the distribution of OGS gateway processing functions (local at OGS or centralised), and for their interconnection. The main technical challenges are discussed, identifying which technologies will be required for an operational VHTS system with OGS.
KEYWORDS: Satellites, Analog electronics, Modulation, Atmospheric optics, Channel projecting optics, Radio optics, Wavelength division multiplexing, Ka band, Digital signal processing, Atmospheric propagation
The paper deals with an analysis of very High Throughput Satellite (VHTS) systems employing optical feeder links. To do so, a fixed set of user requirements is selected that allows for different optical feeder link options to be compared and evaluated on a common basis. The main system aspects are discussed and a rough assessment of the payload resources in terms of mass, power and dissipated power required for each is provided. This exercise reveals important trade-offs and new research avenues for the optical communications community.
For the last three years the European deep-space optical communications program had been based on the Asteroid Impact Missions (AIM), a rendezvous mission with the double-Asteroid Didymos. Unfortunately, the AIM mission was not approved by ESA council and efforts are now concentrated on the implementation of a Deep-space Optical Communication System (DOCS) in a Space Weather (SWE) mission to libration orbit L5 within the frame of ESA’s Space Situational Awareness (SSA) program. DOCS is an in-orbit technology demonstration that also serves a scientific objective, namely the transfer of high-resolution solar imagery. The characteristics of the SWE L5 mission allow significant simplifications in deep-space optical communication terminal design, because the equidistant triangular orbital geometry between the sun, the Earth and L5 (all three distances are 1 AU = 150 Mio km) ensures that the sun is always separated by 60 degrees from both, the space and the ground terminal. This allows for very efficient solar stray-light shielding and thermal management. It also minimizes the pointing requirements of the DOCS space terminal; a coarse pointing mechanism is not required, nor is a point ahead mechanism. The SSA SWE L5 mission Phase A, Phase B1 and B2 studies will be conducted 2017 - 2019. DOCS aims to demonstrate a data rate of 10 Mbps over 150 Mio km to a 4 m optical ground station. The paper will give an overview of deep-space optical communication technology developments and present the design and performance of the Deep-space Optical Communication System (DOCS).
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