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An Internet datagram delivery service between space systems only provides end-to-end addressability. Building systems and performing actual spacecraft operations requires a variety of services operating over the Internet datagram delivery service. This paper discusses ways to use the capabilities of the upper layer Intemet protocols to support the varied communication needs of satellites. It focuses on protocols in the transport layer (layer 4) and application layer (layer 7) which use the basic packet delivery capabilities of the Internet Protocol (IP) and the network layer (layer3). The transport layer primarily adds data stream multiplexing and reliable data delivery options for use by applications. Data stream multiplexing is provided by the port mechanism in the User Datagram Protocol (UDP) and the Transport Control Protocol (TCP). UDP provides a basic packet delivery service similar to that used in today's spacecraft while TCP provides an automatic retransmission capability for reliable data stream delivery. Data streaming is also supported by the Real Time Protocol (RTP) which operates over UDP. Each of these protocols has benefits and limitations in various space communication environments with a range of link errors, propagation delays, and bit rates. Transport protocol selection and operational usage are discussed with respect to satellite communication requirements. Finally, actual spacecraft operations are performed by using applications running over transport protocols. The use of standard Internet applications such as NTP, FTP, SMTP, and telnet is discussed with respect to satellite operational requirements. The actual use and performance of many of these protocols by the Operating Missions as Nodes on the Internet (OMNI) project at NASNGSFC on orbit with the UoSAT-12 spacecraft is also described. OVERVIEW OF INTERNET PROTOCOLS IN SPACEThe goal of the OMNI project is to defme and demonstrate an end-to-end communication architecture for future space missions. The authors have combined their knowledge and experience in Internet technologies and space communication systems in developing the following end-toend data communication concept. End-to-End Network ConceptThe data communication requirements of many advanced space missions involve seamless, transparent connectivity between space-based instruments, investigators, groundbased instruments and other spacecraft. The key to an architecture that can satisfy these requirements is the use of applications and protocols that run on top of the Internet Protocol[l] (E). IP is the technology that drives the public Internet and therefore draws billions of dollars annually in research and development funds. Most private networks also utilize Ip as their underlying protocol. IP provides a basic standardized mechanism for end-to-end communication between applications across a network. The protocol provides for automated routing of data through any number of intermediate network nodes without affecting the endpoints. Proposed ArchitectureRecognizing the clear bene...

Ongoing work at National Aeronautics and Space Administration Goddard Space Flight Center (NASA/GSFC), seeks to apply standard Internet applications and protocols to meet the technology challenge of future satellite missions. Internet protocols and technologies are under study as a future means to provide seamless dynamic communication among heterogeneous instruments, spacecraft, ground stations, constellations of spacecraft, and science investigators. The primary objective is to design and demonstrate in the laboratory the automated end-to-end transport of files in a simulated dynamic space environment using off-the-shelf, low-cost, commodity-level standard applications and protocols. The demonstrated functions and capabilities will become increasingly significant in the years to come as both earth and space science missions fly more sensors and the present labor-intensive, mission-specific techniques for processing and routing data become prohibitively. This paper describes how an IP-based communication architecture can support all existing operations concepts and how it will enable some new and complex communication and science concepts. The authors identify specific end-to-end data flows from the instruments to the control centers and scientists, and then describe how each data flow can be supported using standard Internet protocols and applications. The scenarios include normal data downlink and command uplink as well as recovery scenarios for both onboard and ground failures. The scenarios are based on an Earth orbiting spacecraft with downlink data rates from 300 Kbps to 4 Mbps. Included examples are based on designs currently being investigated for potential use by the Global Precipitation Measurement (GPM) mission.

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Keith.Hogie@gsfc.nasa.govAbsfract-The first step in using Intemet Protocols in space is to establish the basic Internet datagram delivery service over satellite RF links. This paper discusses the low-level data link and data routing issues related to using Internet protocols to support spacecraft communications. It covers issues related to layer 1 (physical), layer 2 (data link), and layer 3 (network). It does NOT cover layer 4 (transport) and above. At the physical layer, the paper presents various applications of forward-error-correction (FEC) coding techniques, such as convolutional coding and Reed-Solomon. It describes approaches for using these techniques in ways that are independent of the protocols used at the data link layer and above. At the data link layer, common, commercially available framing schemes are discussed along with how they can be easily deployed. A rationale is provided for the selection of HDLC/frame relay ftaming along with IETF multi-protocol encapsulation. At the network layer, the Internet Protocol end-to-end addressability and routing is discussed in the context of space-based applications. Standard solutions for dealing with the intermittent and mobile links of satellites are also discussed. These include a discussion of Mobile IP and mobile routing protocols. Finally, deployment of these protocols in both spacecraft and ground systems are discussed. Details of current implementations by the Operating Missions as Nodes on the Intemet (OMNI) project at NASNGSFC using operational space and ground systems such as are also provided.