A Highly Reliable, Streamlined Method for High- and Low-Rate Avionics Communication 

How it works

The SpaceWire specification is a set of serial links that describe a network fabric used to move information defined in packets. NASA Goddard’s SpaceWire design is the first and most mature of its kind in the United States. New features and enhancements to the NASA SpaceWire core make the design more suitable for space flight applications. A sophisticated verification environment includes directed and random testing, helping to detect hard-to-find design bugs and making the design simple to maintain and update. Not all features are included in the SpaceWire standard, but Goddard’s design may be configured so that it is completely compatible with it. These significant advantages enable easy system integration and testing of SpaceWire designs while improving reliability and reducing complexity.

Specific to Goddard’s SpaceWire design, the link and switch is a unique implementation of the SpaceWire specification, which enables avionics computers to seamlessly communicate at varying data rates (2 Mbps to more than 200 Mbps), minimizing interconnects. The communication allows resources to be distributed and provides for redundancy across space-flight applications.

Goddard’s link-and-switch implementation provides for several additional features that add to the reliability and usability of the SpaceWire standard for space-flight applications. Redundant physical interfaces (cables) added to the design simplify operation because the user does not need to interact with the design. Goddard has also designed time-code enhancements to the protocol by allowing multiple time-code masters to operate on the network simultaneously. These low-latency broadcast pulses are sent over a SpaceWire network to signal an event, interrupt an event, or distribute time information. In addition, a new zero-jitter time code reduces uncertainty as to when the time-code signal arrives at all destinations. Goddard has also designed the link and switch for high accuracy with design verification using direct and random testing. This means that all parameters of the design are randomized and tested in a continual loop (indefinitely, if needed) to find errors or situations that may be difficult to anticipate.

Why it is better

The SpaceWire standard itself offers advantages over other communication protocols for space-flight applications. The IEEE 1355 specification, a leading alternative, offers functionality similar to SpaceWire but suffers from ambiguities that may make two different implementations of the specification not compatible. In contrast, Goddard’s link-and-switch implementation of the SpaceWire standard leaves no ambiguities in its interpretation and can be used with other SpaceWire implementations without compatibility problems.

Goddard’s link-and-switch implementation also provides many advantages for space-flight applications over the current SpaceWire capabilities. Specifically, the redundant physical interfaces eliminate the need for the user to be involved in finding the most reliable data connection. These features may reduce the complexity that worm-hole routing may introduce into a network, helping to prevent network blockage.

In addition, unlike the current SpaceWire standard, which only provides for one time-code master, Goddard’s implementation allows for up to four masters, or people, on the network who can send time-code signals. For space-flight applications, this feature allows more out-of-band signaling between nodes in the network, enhancing flexibility in the system design.

Crucial for space-flight applications is the implementation’s provision for both random and directed testing. This combination of testing helps improve the reliability of communications in space-flight applications in which accurate data transmission is critical. This feature makes Goddard’s design the most robust SpaceWire implementation available to date.

Finally, Goddard’s design is uniquely optimized for size and speed by separating functions into easily manageable partitions.