NASA/TM—2003-212187 Architecture Study of Space-Based Satellite Networks for NASA Missions William D. Ivancic Glenn Research Center, Cleveland, Ohio August 2003 The NASA STI Program Office . in Profile Since its founding, NASA has been dedicated to • CONFERENCE PUBLICATION. Collected the advancement of aeronautics and space papers from scientific and technical science. The NASA Scientific and Technical conferences, symposia, seminars, or other Information (STI) Program Office plays a key part meetings sponsored or cosponsored by in helping NASA maintain this important role. NASA. The NASA STI Program Office is operated by • SPECIAL PUBLICATION. Scientific, Langley Research Center, the Lead Center for technical, or historical information from NASA’s scientific and technical information. 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Ivancic Glenn Research Center, Cleveland, Ohio Prepared for the 2003 Aerospace Conference sponsored by the Institute of Electrical and Electronics Engineers Big Sky, Montana, March 8–15, 2003 National Aeronautics and Space Administration Glenn Research Center August 2003 Available from NASA Center for Aerospace Information National Technical Information Service 7121 Standard Drive 5285 Port Royal Road Hanover, MD 21076 Springfield, VA 22100 Available electronically at http://gltrs.grc.nasa.gov Architecture Study of Space-Based Satellite Networks for NASA Missions William D. Ivancic National Aeronautics and Space Administration Glenn Research Center Cleveland, Ohio 44135 Summary Traditional NASA missions, both near Earth and deep space, have been stovepipe in nature and point-to-point in architecture. Recently, NASA and others have conceptualized missions that required space-based networking. The notion of networks in space is a drastic shift in thinking and requires entirely new architectures, radio systems (antennas, modems, and media access), and possibly even new protocols. A full system engineering approach for some key mission architectures will occur that considers issues such as the science being performed, stationkeeping, antenna size, contact time, data rates, radio-link power requirements, media access techniques, and appropriate networking and transport protocols. This report highlights preliminary architecture concepts and key technologies that will be investigated. Introduction Traditional NASA missions, both near Earth and deep space, have been stovepipe in nature and point-to-point in architecture. There was no notion or need to communicate directly with other spacecraft. All communications (command, control, and data) went to a customized ground infra- structure either directly or via NASA’s Tracking and Data Relay Satellite System (TDRSS). NASA and others have conceptualized and are beginning to plan missions that require space-based network- ing. The Earth Science Technology Office sensor web concept is a prime example. The notion of networks in space is a drastic shift in thinking and requires entirely new architectures, radio systems (antennas, modems, and media access), and possibly even new protocols. Space-based networks, like those envisioned for a sensor web, require far greater resources than NASA alone can provide. A number of cooperating entities including NASA, the Department of Defense (DOD), the European Space Agency, the National Space Development Agency and others will provide these systems. Thus, common communication packages need to be developed that allow these space-based systems to interoperate. NASA Glenn Research Center will be performing an architecture and system engineering study. This study will address space-based satellite networks primarily for NASA missions; however, dual-use capabilities will be considered. This will allow common subsystems to be utilized by other satellite users such as other government agencies (U.S. or otherwise) and commercial entities. A full system engineering approach for some key mission architectures will occur that considers issues such as the science being performed, stationkeeping, antenna size, contact time, data rates, radio-link power requirements, media access techniques, as well as networking and appropriate transport protocols. These space-based network architecture designs will be developed to be evaluated in a preliminary design review with critical systems investigated further. This report highlights preliminary architecture concepts and key technologies that will be investigated. NASA/TM—2003-212187 1 Design Philosophy There are often numerous solutions to a given network design problem. Wherever possible, we wish to develop networks that can be designed with techniques and technologies already in place in the telecommunications and computer information industries. By doing so, we should be able to dramatically reduce the cost, deployment time, and risk. Architecture Concepts In order to limit the problem, three main architecture concepts will be considered: (1) A myriad of loosely coupled ground stations in support of low-Earth-orbit (LEO) spacecraft (2) A fully meshed sensor web (3) A formation-flying constellation where the entire constellation performs as one unit Each architecture has unique problems that must be addressed. Our goal is to see if common solutions exist to these problems. In addition, we would like to determine if there are similar problems that exist in terrestrial systems. If so, there already may be solutions that NASA can use outright or adapt. Likewise, there may be a similar problem existing in the terrestrial communica- tions networks, which has yet to be solved. NASA may be able to provide the additional motivation needed to encourage industry to cooperate and collaborate in solving this problem. A Myriad of Ground Stations Traditionally, LEO satellites have been designed to communicate to the ground either directly or via a relay satellite. Those missions that communicate directly to the ground require the satellites and ground stations to be highly scheduled and coordinated. The ground stations are programmed to know exactly when and where to track the satellites. In addition, a rather limited set of ground stations are involved. Often the satellites are in polar orbits and the stations are near the Polar Regions to allow for maximum connection time (refs. 1 and 2). These satellites often utilize techniques whereby the satellite stores data until it has connectivity with the ground, at which time it forwards the data down at a high rate. For such architectures, the longer the satellite is in isolation, the more data it has to store. This, in turn, requires higher transmission rates to offload the data once a connection is achieved. Thus, this architecture results in rather expensive ground stations that are highly scheduled but have a small duty cycle. In addition, the spacecraft costs increase because of the need for added onboard storage and high-rate communications to the ground. To reduce the overall system cost and increase the number of science missions as well as the amount of science performed by each mission, we propose modification of the traditional LEO satellite direct-to-ground architecture. The paradigm shift we attempt to make is to bring the cost of the ground and space infrastructure down significantly by volume production and sharing of network resources. The basic question becomes “Is it technically, economically, and politically feasible to utilize a myriad of