Low-Earth-orbit (LEO) satellites require both data links for telemetry, tracking and command (TT&C) and for download of mission data (e.g., Earth observation). A single ground station can maintain a contact to a passing LEO satellite for relatively short time only (typically ~10 min), and together with high-resolution sensor systems onboard the satellites producing high amounts of data this leads to a serious bottleneck. In fact, depending on the actual orbit parameters (altitude and inclination) the long-term average visibility as seen from one ground station is only 1% to 6% of the overall orbit time.
State-of-the-art is a costly world-wide network of ground stations. Geostationary-Earth-orbit (GEO) satellites acting as data relays are another elegant possibility to overcome this problem, since the majority of LEO satellites will be visible to the GEO satellite for at least 50% of their orbital period. The advantages for TT&C are obvious, and data download benefits from more relaxed data rates resulting in decreased transmit power requirements onboard the satellite.
The goals of the project GeReLEO were to explore and to demonstrate new key technologies for the realization of GEO data relays for LEO satellites. Through these new technologies, which are assigned to the area of space/satellite communications, the competitiveness of German companies can be improved with respect to satellite modems and payload components.
In detail, the following key innovations were developed:
All components and algorithms were developed as breadboard models (modem, antenna, MEMS switches, etc.) and integrated in a demonstrator system, which was presented in Oberpfaffenhofen on October 25th, 2012 (in German).
The final report (in German) is available in DLR’s electronic library.
The in-orbit verification of the antenna array, the MEMS and FPGA performance and degradation over time are objectives of a successor project called GeReLEO-SMART.
Main objective of the second successor project GeReLEO-MODULOS was the development of an engineering model for a LEO modem with up/down-converters for the Ka-band, physical layer implementation, and data link layer software.
Space Administration of the German Aerospace Center (DLR) under contract no. 50 YB 0907, with funds of the German Federal Ministery of Economics and Technology (BMWi) based on a decision of the German Bundestag.
01.10.2009 - 30.11.2012
DLR Institute of Communications and Navigation (KN) – project coordination
Astrium - BD Telecommunications Satellites – subcontractor of DLR-KN
EADS Innovation Works Germany
Fraunhofer Institute for Electronic Nano Systems
SINTEC Microwave Systems GmbH
Steinbeis Innovation Center for Space
Technische Universität München, Institute for Communications and Navigation