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TDRSS Demand Access System augmentation

The Demand Access System (DAS) of the Tracking and Data Relay Satellite System (TDRSS) enables space borne and ground based Space Network (SN) customers to send their telemetry and science data 24 hours a day without having to schedule network services. DAS uses Tracking and Data Relay Satellite (TDRS) Multiple Access (MA) antennas and spread spectrum modulation. The current DAS system, installed in 2004, is limited in several ways and becoming obsolete due to outdated technology. A new DAS concept that takes advantage of newer technologies and low-cost components to provide enhanced customer service has been developed as a potential replacement of the existing system. The new concept does away with the hardware resource limitations of the previous system, and its performance is limited only by the self-interference generated by the MA users. In contrast to the previous system, which is largely a custom design, the new system makes use of Commercial-Off-The-Shelf (COTS) products and offers additional features such as seamless TDRS handovers and TDRS arraying. The system is self-contained in terms of handling all user interactions, and can be updated easily without impacting the rest of the SN infrastructure; backward compatibility is also maintained. Plans are underway to demonstrate the initial concept at the White Sands Complex (WSC) ground terminal by shadowing several orbiting DAS customers. Details of the system architecture, and design approach are presented.