Ultra-high-speed data relay systems

The wide bandwidth offered by optics and advanced multiplication techniques, may increase the available capacity of the space communication channel. At optical frequencies, the background noise due to Sun irradiation may become limitative and bring the system out of service. It is worth to evaluate the impact this kind of noise has on a communication system based on optical technology. In particular different architecture may be affected by different noise levels. Thus, the most suitable scenario for optical intersatellite links can be defined in terms of minimum background noise. Two scenarios will be compared. The first one is based on LEO-GEO optical link, the second one on GEOGEO optical link. In both cases data are collected from a formation flying satellite cluster, whose dasiamotherpsila establish a communication link with a geostationary satellite. The high amount of data requires wide capacity link to reduce the on board hard memory dimension and reduce the communication duration.

A double-layered constellation for a future global satellite communications network connected by optical intersatellite links has been proposed. The constellation consists of lower layer satellites for mobile and personal satellite communications, and upper layer satellites for large- capacity fixed satellite communications and feeder links. Optical inter-satellite links, which can perform high-capacity communications with small terminals, are used for all intersatellite data transmission. Although a polar orbit constellation offers the merit of simpleness in network configurations, the inclined orbit constellation offers the potential for reducing the required number of satellites, improving link properties, and enhancing the coverage in middle and low latitudes, by selecting the most adequate inclination of the orbits. The optical inter- satellite link properties, coverage properties, and required number of satellites are evaluated for constellations using inclined orbits, and then compared with those of a polar orbit constellation. Three constellation types in each layer achieving continuous double coverage are assumed. For each constellation, the relations between these properties and the inclination of the orbits are examined. The basic parameters of optical inter-satellite links on satellite constellations using inclined orbits are also shown.

The development of optical communications systems from long fibers to compact wireless networks has led to the possibility of linking two satellites using a wireless optical link. The optical communication systems have been upgraded to use of wireless systems. The two satellites can be connected using optical wireless link. The optical wireless communication allows the exchange of information between two satellites at a higher speed. To act as a source of light, laser can be used and as an optical link, and a high-frequency light signal can be used. In this paper, we are analyzing and optimizing the different aspects of an optical communication link by selecting different modulation scheme. The IS-OWC link has been analyzed using PSK, DPSK, and OQPSK. The bit error rate (BER) and Q-factor have been used as the main determinant to analyze the performance of optical link between two satellites.

Disruption-tolerant networks (DTNs) are groups of network assets connected with a suite of communication protocol technologies designed to mitigate the effects of link delay and disruption. Application of DTN protocols to diverse groups of network resources in multiple sub-networks results in an overlay network-of-networks with autonomous data routing capability. In space environments where delay or disruption is expected, performance of this type of architecture (such as an interplanetary internet) can increase with the inclusion of new communications mediums and techniques. Space-based optical communication links are therefore an excellent building block of space DTN architectures. When compared to traditional radio frequency (RF) communications, optical systems can provide extremely power-efficient and high bandwidth links bridging sub-networks. Because optical links are more susceptible to link disruption and experience the same light-speed delays as RF, optical-enabled DTN architectures can lessen potential drawbacks and maintain the benefits of autonomous optical communications over deep space distances. These environment-driven expectations - link delay and interruption, along with asymmetric data rates - are the purpose of the proof-of-concept experiment outlined herein. In recognizing the potential of these two technologies, we report an initial experiment and characterization of the performance of a DTN-enabled space optical link. The experiment design employs a point-to-point free-space optical link configured to have asymmetric bandwidth. This link connects two networked systems running a DTN protocol implementation designed and written at JPL for use on spacecraft, and further configured for higher bandwidth performance. Comparing baseline data transmission metrics with and without periodic optical link interruptions, the experiment confirmed the DTN protocols' ability to handle real-world unexpected link outages while maintaining capability of reliably delivering data at relatively high rates. Finally, performance characterizations from this data suggest performance optimizations to configuration and protocols for future optical-specific DTN space link scenarios.

Experiments were conducted to evaluate the viability of commercial-off-the-shelf (COTS) technology in the design of high-performance optical intersatellite communications links. The optical links were operated at 155, 622 and 2488 Megabits per second (Mbps) and at 1550 nm wavelength. Communications components were evaluated against performance parameters for on-off keyed (OOK) systems. Transmitters, receivers, optical amplifiers, and filters, used to minimize the impact of amplified spontaneous emission (ASE), were characterized individually and within system configurations. Bit error rate (BER) as a function of photons per bit was characterized for several system configurations. Extinction ratio analysis experiments were conducted to determine the limiting factors on the systems performance. Widely varying optical powers in space (for low earth orbit) imply a robust receiver dynamic range requirement. Dynamic range of COTS receivers was examined and resulted in sufficient performance. In addition, gamma radiation tests on fiber amplifiers were also evaluated in a system context.

For high-speed space communications, future needs of space optical communication technologies are further increasing to provide operation services of intersatellite links and direct links in the field of remote sensing and space explorations. However, cloud blockage of direct communication links is one of the issues in space optical direct communications, while the atmospheric effect on the communication links is also an important issue on the link quality in a given satellite path connected with optical ground stations. Space optical communication experiments have been performed and results have also been reported internationally, but many of them are mainly focused on communication link evaluations for stable optical direct links under atmosphere, while experiments of optical ground systems for avoidance of cloud blockage with ground network switching controls have not been sufficiently reported. For the network switching controls among optical ground stations based on cloud blockage on a given satellite path over stations, JAXA developed ground network systems. First, the laser ground network planning system is explained. Next, our optical ground stations and the infrared cloud monitoring and discrimination system for lower cloud blockage are explained. Finally, our planned network switching testings are explained.

Laser Communication Links in Orbit have become routine for Alphasat TDP1 GEO data relay and Sentinel-1A LEO satellite. Since November 2014, an extensive campaign has demonstrated stable and bit-error free links over distances of up to 45.000km with 1.1W optical transmit power and data rates of up to 1.8Gbps. Link acquisition is achieved reliably within less than 55s. Links with low grazing altitude investigate the impact of atmosphere to link performance. The optical links between Sentinel-1A and Alphasat are in collaboration of ESA, DLR, and TESAT Spacecom. Alphasat TDP1 is the precursor for European Data Relay Satellite System EDRS [1].

Rapid increases in global broadband demand are driving advanced commercial Low Earth Orbit (LEO) satellite communications systems that can deliver global broadband capacity at terrestrial level costs and performance. Flight demonstration programs such as the Defense Advanced Research Projects Agency (DARPA) "Blackjack" program are exploring the utility of Optical Inter-Satellite Links (OISLs) for these new LEO systems. For global communications, LEO systems, such as that being developed by Telesat, provide unprecedented broadband capabilities. Telesat's new LEO system, Telesat Lightspeed, will deliver very low latency, fiber-like mesh connectivity via OISLs, increasing the capabilities for data dissemination and delivery across the globe. The ability for a User Terminal (UT) to opt to reach back without the need for anchor relay stations through multiple OISL hops between communication satellites, provides secure and resilient connectivity. Global (including the polar) connectivity, at fiber-like speeds, provides a dramatic change to high-capacity data distribution and dissemination while delivering robust reliable and trusted information. This paper will provide an architectural overview of the Telesat Lightspeed mesh network interfaces, including OISL spacecraft-to-spacecraft relay connectivity, as well as the integration of User Terminals, landing stations, satellite operations centers, and network operations centers. Satellites operating in both polar and inclined orbit planes and cutting-edge technologies, including phased array antennas, onboard data processing and OISLs, enable pole-to-pole global coverage, along with the ability to concentrate capacity in areas where it is most needed to maximize network efficiency and achieve superior unit cost economics. We identify and address challenges associated with operating OISLs including acquisition, tracking, tasking, efficient data routing, and managing network data. Lastly, we present enabling standards and technologies that enhance network flexibility, interoperability and identify areas of future capability development.

Kepler Communications presents the results of space-to-ground and space-to-air optical link testing using its prototype Space Development Agency (SDA)-compatible low Earth orbit (LEO) satellites. Kepler’s two optical prototype satellites launched in November 2023 and each host a single TESAT SCOT80 optical communications terminal (OCT) compatible with v2.1.2 (T0) of the SDA Optical Communications Standard. Since closing our first optical inter-satellite link (OISL) in June 2024, Kepler has demonstrated link acquisition and data transfer between its satellites and numerous optical ground terminals (OGTs) and optical-equipped aircraft in flight, using terminals built by different manufacturers, operated by various partners, and across a range of link conditions. We describe the test setup including the satellite, ground, and aircraft optical equipment. We also explain the process for coordinating space-to-ground and space-to-air links, which begins weeks in advance, continues through day-of weather checks, satellite tasking, OCT acquisition parameters, and flight plan filing, and concludes with post-contact analysis of results and troubleshooting if necessary. Flight test planning comes with unique challenges including weather, wind speed, and airspace restrictions. Because there is currently no way to transmit the aircraft’s position to the satellite in real time, the aircraft’s flight test route must be planned out advance, defined by a set of [WGS84 longitude, WGS84 latitude, WGS84 altitude, UTC time] waypoints. During the ≈10-minute satellite pass, the aircraft’s actual position must match its planned position within ≈500 meters (±10 seconds depending on groundspeed). We describe validated methodologies to minimize aircraft position/timing error while also minimizing pilot workload. In January 2026, Kepler is launching its next ten operational space data relay satellites, with a total of forty SDA-T1- compatible (v3.0.1) OCTs, which will continue performing commercial and government space-to-space, -ground, and -air optical link operations beginning in 2026. Once completed, Kepler’s optical space data relay network will provide users with gigabit, sub-second internet connectivity anywhere in LEO and with significant coverage of the Earth’s atmosphere and surface.

The growing demand for high-speed broadband communications with low orbital or geostationary satellites is a major challenge. Using an optical link at 1.55 μm is an advantageous solution which potentially can increase the satellite throughput by a factor 10. Nevertheless, cloud cover is an obstacle for this optical frequency. Such communication requires an innovative management system to optimize the optical link availability between a satellite and several Optical Ground Stations (OGS). The Saint-Exupery Technological Research Institute (France) leads the project ALBS (French acronym for BroadBand Satellite Access). This initiative involving small and medium enterprises, industrial groups and research institutions specialized in aeronautics and space industries, is currently developing various solutions to increase the telecommunication satellite bandwidth. This paper presents the development of a preliminary prediction system preventing the cloud blockage of an optical link between a satellite and a given OGS. An infrared thermal camera continuously observes (night and day) the sky vault. Cloud patterns are observed and classified several times a minute. The impact of the detected clouds on the optical beam (obstruction or not) is determined by the retrieval of the cloud optical depth at the wavelength of communication. This retrieval is based on realistic cloud-modelling on libRadtran. Then, using subsequent images, cloud speed and trajectory are estimated. Cloud blockage over an OGS can then be forecast up to 30 minutes ahead. With this information, the preparation of the new link between the satellite and another OGS under a clear sky can be prepared before the link breaks due to cloud blockage.

Free Space Optical (FSO) communication is a low cost and license free high bandwidth access technique, is a primary research area from last few years. Atmospheric turbulence plays a vital role in degrading the link performance. This paper presents the model study on the effects of atmospheric turbulence in FSO links. The study is based on the most popular gamma-gamma model distribution. The theoretical model is simulated by varying the height of link and the results are plotted in Mathworks® MATLAB®. The research demonstrates that the effects of turbulence depend primarily on wind speed and height of established FSO link. After varying the height of link, the effects of atmospheric turbulence on link performance can be clearly seen. The result also plotted for the attenuation of signal with varying visibility range conditions.

The integration of optical communication links into space networks via Disruption Tolerant Networking (DTN) is a largely unexplored area of research. Building on successful foundational work accomplished at JPL, we discuss a multi-hop multi-path network featuring optical links. The experimental test bed is constructed at the NASA Glenn Research Center featuring multiple Ethernet-to-fiber converters coupled with free space optical (FSO) communication channels. The test bed architecture models communication paths from deployed Mars assets to the deep space network (DSN) and finally to the mission operations center (MOC). Reliable versus unreliable communication methods are investigated and discussed; including reliable transport protocols, custody transfer, and fragmentation. Potential commercial applications may include an optical communications infrastructure deployment to support developing nations and remote areas, which are unburdened with supporting an existing heritage means of telecommunications. Narrow laser beam widths and control of polarization states offer inherent physical layer security benefits with optical communications over RF solutions. This paper explores whether or not DTN is appropriate for space-based optical networks, optimal payload sizes, reliability, and a discussion on security.

The growth in interest for space-based optical communications has been significant in the recent years. The high data-rate capability, together with a reduced system footprint, make such technology appealing for governmental and commercial communications applications. While inter-satellite optical links are now regarded as a stable technological solution, especially for mega-constellations, Ground-to-Space links (or Feeder Links) still require a refinement in design before reaching the widespread use. This is mostly because the optical Feeder Link has to withstand optical perturbations induced by the atmospheric turbulence, affecting both the uplink and downlink directions in a different manner and extent. The link budget, and in general the atmospheric fading channel, needs to be carefully assessed to guarantee the required availability for a high-throughput communication link. In the frame of the ESA HydRON vision, the Institute of Communications and Navigation of the German Aerospace Center (DLR-KN) has been developing a suite of solutions to model, simulate and emulate the fading atmospheric channel; the AO compensation; and the fibre coupling effects. These tools are being used to support design decisions for the optical Feeder Link, in different domains. The main outcomes of such developments, and their current applications, are presented in this paper.

Inter Satellite Links (ISL)are essential to connect Satellites operating in a constellation. If these ISLs could manage high data rates in Gigabit per seconds the network becomes a broadband connectivity services. New possibilities for data exchange and independencies from ground networks are offered. LEO satellite constellations with low latency of data streaming, are very attractive as a backhaul infrastructure to connect people worldwide like a Space based Internet or to address Internet of Things (IoT)applications on a global scheme. Optical Inter-Satellite Links (OISL)combine very high data rates with resilient performance. Due to its narrow beam and a coherent detection technology without beacons, these OISLs a very robust. As the optical beams are much narrower than RF beams, no interference with other potential optical communication systems will occur and thus offer high operational security and immunity to interference sources, jamming and eavesdropping. An obvious advantage of the optical ISL is the fact that the frequency usage is not regulated by ITU, which makes the planning and operation of a navigation constellation much easier. OISLs are realized by Laser Communication Terminals (LCT)on each end of the link. The technology readiness of Laser Communication Terminals is TRL9. This paper gives an overview on the current status and on the future developments of Laser communication terminals in the various applications.

The area of digital communications has undergone a significant transformation in the last twenty years due mostly to the discovery of iterative forward error correction (FEC) codes (such as turbo codes) and iterative demodulation techniques (such as turbo equalization). Waveforms developed for the High Frequency (HF) band typically place an interleaver between the FEC scheme and the transmitted symbols. The purpose of this interleaver is to decorrelate the errors caused by slow fading multipath channels encountered on HF. If no interleaver is used, most standard EEC schemes become ineffective (e.g. convolutional codes). Although HF waveforms were not designed with the notion of iterative demodulation techniques in mind, it turns out that these techniques can be applied to single-carrier HF waveforms which utilize FEC and interleaving by iteratively exchanging soft information between the equalizer and the FEC decoder. This paper will investigate the benefits of applying iterative demodulation techniques to the 3200 and 9600 bit per second waveforms defined in STANAG 4539 as a function of the Doppler spread and multipath spread encountered on HF channels.