Avionics on the International Space Station: Present and Future

Abstract

The International Space Station (ISS) provides a unique environment in low-Earth orbit for research and operations. Supporting this goal is a suite of avionics systems that have demonstrated high functionality and reliability: • The Command and Data Handling System provides command and control for core ISS systems. • The Communications and Tracking System provides communications between ISS and ground facilities, as well as within ISS elements. • The Guidance, Navigation, and Control System provides control of ISS attitude and reboost. • The Crew Avionics Interface Equipment System provides laptop computers and supporting hardware used by the ISS crew. • The Integrated Station Local Area Network System provides connectivity among laptop computers, payloads, and other attached devices. This paper provides an overview of the ISS United States (US) avionics hardware systems. It provides an introduction to the performance and architecture of each system, a summary of system experience onorbit to date, and description of planned enhancements to improve performance. COMMAND AND DATA HANDLING SYSTEM The Command and Data Handling System (C&DH) provides command and control for core ISS systems. The system uses a distributed architecture of computers, called Multiplexer/ Demultiplexers (MDMs). The system architecture is depicted in figure 3. Fifty MDMs will control the systems on the ISS. The C&DH subsystem controls the flow of data to and from its processors, responds to crew commands via Personal Computing System (PCS) laptops, as well as commands from the ground via the Communications and Tracking (C&T) System. C&DH is broken into two basic networks: Command and Control (C&C) and Payload networks. Both communicate with one another over MIL-STD-1553 data buses. The Payload network includes Ethernet and high-rate fiber as well as 1553. Communication with payloads utilizes a series of gateways and switches. The C&C network communicates over 1553 and has a high-rate fiber output to the C&T system for downlinking data. The C&DH hardware includes a three-tier architecture of processors as described below: • Tier 1 Enhanced MDMs are triply redundant. They provide command and control over lower-tier processors, maintain system synchronization, 54th International Astronautical Congress of the International Astronautical Federation, the International Academy of Astronautics, and the International Institute of Space Law 29 September 3 October 2003, Bremen, Germany IAC-03-T.2.02 This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.