Quantum Key Distribution (QKD) systems will play an important role in future networks for secure data communication. In order to provide a global coverage of a future QKD service, satellites are needed to bridge large distances. These satellite systems must be cost efficient to facilitate deployment since many network nodes will be needed. The CubeSat standard is frequently used for New Space projects as a versatile platform for satellite payloads. It is also chosen as a baseline for the construction of the system described in this paper.
The DLR Institute of Communications and Navigation develops optical free space communication systems for scientific research in classical and quantum communications. A previous development of a 1/3 U CubeSat communication terminal for up to 100 Mbit/s downlinks is adapted to be used for quantum communications tests with multiple transmitters. Since the original laser terminal was designed for C-band wavelengths, a redesign of the optical system is needed to achieve polychromatic performance for the three sources. The optical system consists of a fiber collimator, a beam steering system and an afocal telescope. Most important requirement of the latter is a similar magnification for all wavelengths to ensure concentric beams pointing to the OGS. Scenarios in which the system is optimized either for lowest divergences or a similar magnification of the telescope are demonstrated in Figure 1. As the afocal telescope is used bidirectionally, it also needs to be optimized for the incident wave-front of the beacon from the OGS with respect to the beam shape at the four quadrant detector. These parameters are important for a correct pointing control.
A fiber-based wavelength division multiplexer (WDM) is used for combining signals from three sources into one output fiber. As shown in the block diagram in Figure 2, it is based on cascaded thin film interference filters which are coupled to the fibers. Especially the propagation of 850 nm and 1550 nm signals in one single mode fiber is critical. Therefore the types of optical fibers were selected with respect to the bend loss, single mode propagation behavior, polarization integrity and optimal cladding diameter for the production.
KEYWORDS: Satellites, Optical communications, Space operations, Satellite communications, Commercial off the shelf technology, Interfaces, Telecommunications
Space industry has undergone a significant change over the last years. The development moved from large and costly spacecrafts to cost-efficient designs and shorter development times. While the satellites became smaller, the resolution of high compact sensors increased which led to a high data-volume to be transmitted and increasing demands for higher data rates on small satellites. This motivated for a highly compact version of DLR’s optical communication payload OSIRIS for small LEO satellites. DLR’s Institute of Communications and Navigation has developed the OSIRIS (Optical Space Infrared Downlink System) program starting with payloads on the satellites Flying Laptop of Univ. of Stuttgart and BiROS of DLR. Combining miniaturization to the flight-proven developments with novel concepts, OSIRIS4CubeSat allows integration in a standard CubeSat bus. The development of OSIRIS4CubeSat (industrialized under the product name “CubeLCT”) is conducted in close collaboration with Tesat Spacecom, DLR’s commercialization partner. The first implementation will be demonstrated within the PIXL-1-Mission on a 3Unit CubeSat. Furthermore, OSIRIS4CubeSat (O4C) has been chosen to support scientific missions together with university partners in the field of Quantum Key Distribution (QUBE). In the future, the modular design will enable extensions for optical inter-satellite links. This paper will give an overview about the development of the O4C payload and the current status of the PIXL-1- Mission. Furthermore, it will show the adaptation of the payload for the scientific mission QUBE. Besides these projects, the paper will give an outlook for future extensions of the O4C payload and the necessity of high data-rates in other scenarios such as inter-satellite links.
The generated amount of data on high flying platforms like aircrafts, satellites and Unmanned Aerial Vehicles (UAV) increases continuously, due to the technical improvement of modern sensor systems. The resulting demands for higher data rates on airborne and space platforms motivates the development of Laser Communication terminals for aircrafts and satellites in the last years. DLR’s Institute of Communications and Navigation has a successful track record in developing Free Space Optical (FSO) terminals for flying platforms like stratospheric balloons, aircrafts and small satellites to transfer data from moving platforms down to earth in real-time. Beside the advantages of FSO such as high data rates and a secure transfer channel against Radio Frequency (RF) interferences, a direct line of sight is mandatory for a successful link. Traditional RF-Communication is more robust and less effected by atmospheric disturbances or weather conditions. Thus, new system concepts have been developed to benefit from the provided high data rates of the FSO and the reliability of RF-Communication technologies. As part of this trend, DLR has developed and demonstrated a Hybrid FSO/RF-communication system capable of overcoming the spurious effects of the atmosphere. This paper gives an overview about DLR’s current studies and developments with the goal to combine the advantages of FSO and RF-Communication. It discusses possible implementation concepts on different platforms and presents experimental results of the implemented FSO/RF hybrid communication system operating for airborne, optical downlinks at 1Gbps.
Optical satellite links have gained increasing attention throughout the last years. Especially for the application of optical satellite downlinks. Within the OSIRIS program, DLR's Institute of Communications and Navigation develops optical terminals and systems which are optimized for small satellites. After the successful qualification and launch of two precursor terminals, DLR currently develops OSIRISv3, a 3rd generation OSIRIS terminal with up to 10 Gbps downlink rate, and OSIRIS4Cubesat, a miniaturized version optimized for Cubesat Applications. The University of Stuttgart's Institute of Space Systems develops small satellites, which are used to demonstrate novel technologies in the Space domain. Together, DLR and University of Stuttgart integrated the first OSIRIS generation onboard the Flying Laptop satellite, which was launched in July 2017 and has been successfully operated since. This paper will give an overview about DLR's OSIRIS program. Furthermore, it will show first results of OSIRISv1 on Flying Laptop. Therefore, the Flying Laptop satellite and OSIRISv1 will be explained. Preliminary results from the validation campaign, where optical downlinks have been demonstrated, will be given.
The German Aerospace Center’s Institute of Communications and Navigation developed the Free Space Experimental Laser Terminal II and has been using it for optical downlink experiments since 2008. It has been developed for DLR’s Dornier 228 aircraft and is capable of performing optical downlink as well as inter-platform experiments. After more than 5 years of successful operation, it has been refurbished with up-to-date hardware and is now available for further aircraft-experiments. The system is a valuable resource for carrying out measurements of the atmospheric channel, for testing new developments, and of course to transmit data from the aircraft to a ground station with a very high data rate. This paper will give an overview about the system and describe the capabilities of the flexible platform. The current status of the system will be described and measurement results of a recent flight campaign will be presented. Finally, an outlook to future use of the system will be given.
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