26 research outputs found
OSIRIS Payload for DLR's BiROS Satellite
Direct optical communication links might offer a solution for the increasing demand of transmission capacity in satellite missions. Although direct space-to-ground links suffer from limited availability due to cloud coverage, the achievable data rates can be higher by orders of magnitude compared to traditional RF communication systems.
DLR’s Institute for Communication and Navigation is currently developing an experimental communication payload for DLR’s BiROS satellite. The OSIRIS payload consists of a tracking sensor for a precise alignment between satellite and groundstation, an optical uplink channel, the two different and independent laser sources and the optical bench with the transmission optics.
This paper will give an overview about the BiROS satellite, the OSIRIS payload and the performance of the system, including space-qualification of the hardware and transmission tests
Verification of Ground Station Diversity for Direct Optical TTC-Downlinks from LEO Satellites by means of an Experimental Laser Source
Most of today's satellites make use of microwave data-links for their TTC-downlinks. However, these data-links are limited in terms of achievable data-rate and spectrum availability. Free-space optical communication links might play an important role in the future, as they outperform microwave links in many relevant parameters, namely terminal-size and -mass, power consumption, and data-rate. A solution taking advantage of these attributes might be the usage of direct optical downlinks from a LEO satellite to an Optical Ground Station (OGS).
The challenge of limited availability due to cloud coverage can be overcome by using Ground Station Diversity with several Optical Ground Stations placed at suitable locations around the globe. With this approach, high link availabilities can be achieved.
The Optical Communication Group of DLR's Institute of Communications and Navigation is currently developing an experimental laser source for compact LEO satellites. The pointing will be accomplished by utilizing the attitude control system of the satellite bus, aligning the source towards an Optical Ground Station during a satellite pass. As no Coarse Pointing Assembly (CPA) is necessary, a system with a low mass (<1kg) and volume can be built. Thus, this concept might be a cost-effective solution for small and compact satellites
with the need for a downlink with a high data-rate.
At first, this paper will describe the experimental payload, a directly modulated laser diode with a relatively low data-rate, which is intended to be used on a compact-satellite. The feasibility of the CPA-less pointing concept will be shown. Data-rates 1Gbit/s are achievable with this approach and relatively small OGS-apertures 60cm, depending on the attitude accuracy of the satellite bus. Then we will give an overview about the Ground Station Diversity concept. Based on cloud coverage data, it will be pointed out that the concept results in link availabilities close to 100%.
A Transportable Optical Ground Station (TOGS) with an aperture of 60cm, which is currently under development, will be also presented. Due to its low mass and easy transportability it can be used to carry out a global validation campaign
DIRECT OPTICAL HIGH SPEED DOWNLINKS AND GROUND STATION NETWORKS FOR SMALL LEO MISSIONS
Direct microwave data downlink capacity of today’s earth observation satellites is limited in terms of available spectrum, transmission data rate, and power consumption. One elegant solution is the use of geostationary data relays satellites which connect to the low flying observation satellite by optical or Ka-band links and do the downlink to the ground station by another Ka-band link. This scenario also allows near real-time data access to the EO-sensors for at least half of the LEO’s orbit. However it also implies efforts in terms of the number of long-range communication terminals employed by one EO-mission. Compact LEOs often cannot afford such a connection due to financial- but also mass- and power-constraints. To enable also these kinds of missions with high rate downlink capacity, small optical terminals can be used that boost the data rate by orders of magnitude compared to today’s RF downlinks. The feasibility of direct optical downlinks from LEO satellites has been demonstrated recently with the laser terminals onboard JAXA’s OICETS and onboard the German TerraSAR-X.
As such direct optical downlinks are hindered by cloud cover, a ground station network is required to ensure a certain required average downlink capacity, independent from the cloud situation. For one thing each optical ground station should be situated in a region with low cloud cover in general. But also the different ground stations of one network should be spaced far apart as to avoid correlation of their cloud cover statistics. Furthermore in a global ground station network, sites north and south of the equator are seasonal de-correlated.
DLR’s Optical Communications Group is investigating the feasibility of direct optical LEO downlinks theoretically and practically together with partners [1], [2], [3]. The performance of optical downlinks has been evaluated by long-term global cloud statistics with different sets of ground station combinations. Furthermore, downlink campaigns shall be performed in near future with simple optical downlink sources on small LEO missions, verifying the theoretical findings. A Transportable Optical Ground Station (TOGS) will be used to carry out these trial campaigns
Transportable optical ground station for high-speed free-pace laser communication
Near real-time data downlinks from aircrafts, satellites and high altitude platforms via high-speed laser commu- nication links is an important research topic at the Institute of Communications and Navigation of the German Aerospace Center (DLR). Ground stations for such scenarios are usually fixed at a certain location. With a mo- tivation to provide a ground station that is quickly and easily deployed anywhere in the world, a transportable optical ground station (TOGS) has been developed. TOGS features a pneumatically deployable Cassegrain-type telescope with main mirror diameter of 60 cm, including optical tracking and receiving system. For calibration of position and attitude, multiple sensors like dual-antenna GPS and inclination sensors have been installed. In order to realize these systems, robust software that operates and controls them is essential. The software is platform independent and is aimed to be used on both mobile and ground terminals. It includes implementa- tion of accurate pointing, acquisition and tracking algorithms, hardware drivers, and user interfaces. Important modules of the software are GPS tracking, optical tracking, star- and satellite tracking, and calibration of the TOGS itself. Recently, a first successful data-downlink from an aircraft to TOGS using GPS tracking has been performed. To streamline the software development and testing process, some simulation environments like mount simulator, aircraft path simulator, tracking camera simulator and tracking error analysis tool have also been developed. This paper presents the overall hardware/software structure of the TOGS, and gives results of the tracking accuracy improvement techniques like GPS extrapolation and optical tracking
Results of the Optical Downlink Experiment KIODO from OICETS Satellite to Optical Ground Station Oberpfaffenhofen (OGS-OP)
Optical LEO downlinks from the Japanese OICETS to the optical ground station built by the German Aerospace Center (DLR) near Munich have been performed. This was the first optical LEO downlink on European grounds. The ground station received a 50-Mbit/s OOK signal at 847 nm on its 40-cm Cassegrain telescope and sent two spatially displaced beacon beams towards OICETS. Five out of eight trials could be performed successfully while the other three were hindered by cloud blockage. A BER of 10-6 has been reached. The elevation angle above the horizon ranged between 2° and 45°. The Fried parameter and the scintillation were measured with instruments inside the ground station. The beacon power received by the LUCE Terminal onboard OICETS has also been recorded. This paper describes the setup of the experiment and highlights the results of the measurement trials
High-speed, high-volume optical communication for aircraft
Transportable ground stations that receive high data volumes from aircraft offer a solution for monitoring unforeseen events
DLR’s Transportable Optical Ground Station
This paper will give an overview about the Transportable Optical Ground Station (TOGS) of DLR’s Institute of Communications and Navigation. Furthermore, a short description of its project involvement will be given
Demonstration of high-rate laser communications from fast airborne platform: flight campaign and results
Some current and future airborne payloads like high resolution cameras and radar systems need high channel capacity to transmit their data from air to ground in near real-time. Especially in reconnaissance and surveillance missions, it is important to downlink huge amount of data in very short contact times to a ground station during a flyby. Aeronautical laser communications can supply the necessary high data-rates for this purpose. Within the project DODfast (Demonstration of Optical Data link fast) a laser link from a fast flying platform was demonstrated. The flight platform was a Panavia Tornado with the laser communication terminal installed in an attached avionic demonstrator pod. The air interface was a small glass dome protecting the beam steering assembly. All other elements were integrated in a small box inside the Pod’s fuselage. The receiver station was DLR’s Transportable Optical Ground Station equipped with a free-space receiver front-end. Downlink wavelength for communication and uplink wavelength for beacon laser were chosen from the optical C-band DWDM grid. The test flights were carried out at the end of November 2013 near the Airbus Defence and Space location in Manching, Germany. The campaign successfully demonstrated the maturity and readiness of laser communication with a data-rate of 1.25 Gbit/s for aircraft downlinks. Pointing, acquisition and tracking performance of the airborne terminal and the ground station could be measured at aircraft speed up to 0.7 Mach
and video data from an onboard camera has been transmitted. Link distances with stable tracking were up to 79 km and distance with data transmission over 50 km. In this paper, we describe the system architecture, the flight campaign and the results