SpaceWire is a

spacecraft A spacecraft is a vehicle that is designed spaceflight, to fly and operate in outer space. Spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth observation, Weather s ...

communication network based in part on the IEEE 1355 standard of communications. It is coordinated by the

European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...

(ESA) in collaboration with international space agencies including

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

JAXA The is the Japanese national air and space agency. Through the merger of three previously independent organizations, JAXA was formed on 1 October 2003. JAXA is responsible for research, technology development and launch of satellites into o ...

, and RKA. Within a SpaceWire network the nodes are connected through low-cost, low- latency,

full-duplex A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow ...

, point-to-point serial links, and

packet switching In telecommunications, packet switching is a method of grouping Data (computing), data into short messages in fixed format, i.e. ''network packet, packets,'' that are transmitted over a digital Telecommunications network, network. Packets consi ...

wormhole routing routers.

Architecture

Physical layer

SpaceWire's modulation and data formats generally follow the data strobe encoding - differential ended signaling (DS-DE) part of the IEEE Std 1355-1995. SpaceWire utilizes

asynchronous communication In telecommunications, asynchronous communication is transmission of data, generally without the use of an external clock signal, where data can be transmitted intermittently rather than in a steady stream. Any timing required to recover data fro ...

and allows speeds between 2 Mbit/s and 200 Mbit/s, with initial signalling rate of 10 Mbit/s. DS-DE is well-favored because it describes modulation, bit formats, routing, flow control, and error detection in hardware, with little need for software. SpaceWire also has very low error rates, deterministic system behavior, and relatively simple digital electronics. SpaceWire replaced old PECL differential drivers in the physical layer of IEEE 1355 DS-DE by low-voltage differential signaling (LVDS). SpaceWire also proposes the use of space-qualified 9-pin connectors. SpaceWire and IEEE 1355 DS-DE allows for a wider set of speeds for data transmission, and some new features for automatic failover. The fail-over features let data find alternate routes, so a spacecraft can have multiple data buses, and be made fault-tolerant. SpaceWire also allows the propagation of time interrupts over SpaceWire links, eliminating the need for separate time discretes.

Link layer

Each transferred character starts with a parity bit and a data-control flag bit. If data-control flag is a 0-bit, an 8-bit LSB character follows. Otherwise one of the control codes, including end of packet (EOP).

Network layer

The network data frames look as follows: One or more address bytes are used for the routing. Addresses are either physical ones (0–31), or logical ones. The difference is that the physical addresses are deleted from the frame header during routing - which is used for hop-based routing (based on path specified in the frame itself). Logical addresses may be deleted as well, depending on the router configuration.

Interconnection

The hardware devices may be connected either directly, or via a SpaceWire router. In the former case, usually pairs of devices are used to guarantee a fail-safe operation, which is handled by the software. A SpaceWire router is usually a

crossbar switch In electronics and telecommunications, a crossbar switch (cross-point switch, matrix switch) is a collection of switches arranged in a Matrix (mathematics), matrix configuration. A crossbar switch has multiple input and output lines that form a ...

-type device, operating in wormhole switching mode. This also may limit the speed of the communication to the lowest common speed. The routing decisions are based on the programmed routing table and the initial incoming frame contents.

Uses

SpaceWire is used all around the globe. Its use began primarily in ESA projects, but it is currently used by

, RKA, and many other organizations and companies. Some NASA projects using it include the

James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope designed to conduct infrared astronomy. As the largest telescope in space, it is equipped with high-resolution and high-sensitivity instruments, allowing it to view objects too old, Lis ...

, Swift's Burst Alert Telescope, the

Lunar Reconnaissance Orbiter The Lunar Reconnaissance Orbiter (LRO) is a NASA robotic spacecraft currently orbiting the Moon in an eccentric Polar orbit, polar mapping orbit. Data collected by LRO have been described as essential for planning NASA's future human and robotic ...

, LCROSS, the Geostationary Operational Environmental Satellite (GOES-R), and the SCaN Testbed, previously known as the Communications, Navigation, and Networking Reconfigurable Testbed (CoNNeCT). It has also been selected by the

United States Department of Defense The United States Department of Defense (DoD, USDOD, or DOD) is an United States federal executive departments, executive department of the federal government of the United States, U.S. federal government charged with coordinating and superv ...

for Operationally Responsive Space. SpaceWire initiatives are being coordinated between several space agencies in the frame of Consultative Committee for Space Data Systems (CCSDS) in order to extend its communication model to the network and transport layers of the

OSI model The Open Systems Interconnection (OSI) model is a reference model developed by the International Organization for Standardization (ISO) that "provides a common basis for the coordination of standards development for the purpose of systems inter ...

. SpaceWire supports highly fault-tolerant networks and systems, which is one reason for its popularity.Dr Barry M Cook; Paul Walker
"Ethernet over SpaceWire - software issues"
4links.co.uk, p. 2

Protocols

The ESA has a draft specification in place for the Protocol ID. The following Protocol ID's have been assigned in ECSS-E-ST-50-51C:

References

Other sources

ESA-

ESTEC The European Space Research and Technology Centre (ESTEC) is the European Space Agency's main technology development and test centre for spacecraft and space technology. It is situated in Noordwijk, South Holland, in the western Netherlands, alth ...

. * [http://www.ecss.nl/forums/ecss/_templates/default.htm?target=http://www.ecss.nl/forums/ecss/dispatch.cgi/standards/showFolder/100630 ECSS-E-50-12A (SUPERSEDED only document number has been changed to ECSS-E-ST-50-12C) SpaceWire - Nodes, links, and networks], ESA-

.
ECSS-E-ST-50-11C Draft 1.3 "Space engineering - SpaceWire protocols"

External links

* {{James Webb Space Telescope Computer buses ECSS standards Fault-tolerant computer systems James Webb Space Telescope