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This paper will illustrate the challenges and preliminary solutions in operating the EDRS constellation. The EDRS network will include two communication payloads, one hosted on a dedicated spacecraft and one as piggy-back on a commercial satellite. The two satellites will be positioned in geosynchronous orbit to provide nearglobal coverage for satellites in low earth orbit (LEO). EDRS is designed to reduce time delays in the transmission of large amounts of data and to allow faster access for the end users. This is achieved by using an optical Laser Communication Terminal (LCT) for the link between the LEO and the EDRS payload and a Ka-band link between the EDRS payload and the ground. The latter will be established via three dedicated feeder link ground stations in Europe from where the data is distributed to the users. The users may also use their own ground stations to receive the data directly. By using the EDRS infrastructure extended capabilities for TM/TC operations will be possible with LEO satellites. This will enable short-time changes to the payload timeline and better reactions to anomalies while optimizing the number of necessary ground stations. DLR with its German Space Operations Center (GSOC) plays a major role in the EDRS operations. This role includes design, development and integration of ground infrastructure and operations of the satellites and ground stations. The EDRS concept of operations differs from the conventional communication satellites. Two challenging new technologies will be integrated in order to provide faster data turnaround times and downlink capabilities of up to 1800 Mbit/s: 1. Laser-Optical Inter-satellite link: The large distance between a satellite in GEO and one in LEO makes the pointing of both laser terminals very difficult. Good attitude information and control of both satellites is required. A good quality orbit determination and time synchronisation is vital for good Laser acquisition times and both payloads need to keep accurately track of their fast moving counterparts. Thus, development of the operations concept requires consideration about establishing the interfaces and coordination of operations with the low flying satellites, which are operated by different control centres. 2. Ka-band downlink: The wavelength of the Ka-band signal leads to significant atmospheric and rain attenuation. Thus, requirements for ground stations (for front- and back-end) in terms of pointing accuracy and the specific hardware are very challenging compared to standard S/X/Ku-band ground stations. Careful consideration has to be taken designing the ground stations and during link establishment and station operations. 62nd International Astronautical Congress, Cape Town, SA. Copyright 2011 by Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) |
