John S. Baras


A Direct to Ground Architecture for Supporting Communications for the International Space Station

Alex T. Nguyen

Masters Dissertation, Number: CSHCN MS 2002-3, Year: 2002, Advisor: John S. Baras

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The deployment of the International Space Station (ISS) has opened new opportunities for research in space, providing a unique platform for tele-science, microgravity experiments, human physiology studies, and earth observation. In order to control, gain data from, and interact with these activities from the ground, a communications system that can support this broad range of applications needs to be established.

In this thesis, three communications architectures for the ISS are discussed: 1) using NASA’s Tracking Data Relay Satellite System (TDRSS), 2) using emerging broadband commercial satellite systems to relay data to the ground, and 3) communicating directly to the ground ("DTG").

The thesis will focus on the latter option, DTG, and establish a methodology for determining the optimum placement of ground terminals for this type of service. A simulation model is developed for a large image file download application, and a detailed coverage analysis of the ISS communicating directly to these ground facilities is performed.

In addition, a bottom-up cost estimate of this architecture is developed and compared to the costs of the other two architectures. The results show that the direct to ground architecture cost is competitive with that of the other architectures, and offers scalability for non-real-time applications.

Coverage provided by commercial Ka-band satellite systems is about the same as that achieved by direct to ground, but its services will likely not be tailored to the needs of the ISS. The TDRS system provides complete coverage, and is therefore good for real-time applications such as videoconferencing.

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