SpaceWire
SpaceWire is a fieldbus that ESA has specified in an ECSS standardization. The bus system transports data serially in full duplex at a speed of up to 200 Mbps. SpaceWire is based on the IEEE 1355-1995 standard, which has been adapted to the requirements in space with regard to its robustness, power consumption and EMC. Some ambiguities in the description have also been eliminated and the link state machine has been improved.
history
The SpaceWire standard was published in January 2003 and has since been used by ESA , NASA , JAXA and Roskosmos in numerous missions and is now also widely used in science, planetary observation and other space travel. Well -known representatives include: Gaia , ExoMarsrover , BepiColombo , James Webb Space Telescope , GOES-R , Lunar Reconnaissance Orbiter and Astro-H
Working principle
SpaceWire Link
The links are point-to-point data connections (P2P) between a node and another node or router. The information can be transmitted in both directions at the same time; each link is full-duplex and bidirectional. The data rate is around 2–200 Mbits / s, and there is occasional documentation that mentions 400 Mbits / s. The data are transmitted in a serial bit stream, using two signals per direction (data & strobe). The signals are transmitted using Low Voltage Differential Signaling ( LVDS ), which requires two wires per signal. A suitable SpaceWire cable therefore consists of four shielded twisted pairs.
SpaceWire packages
A package in the SpaceWire begins with an addressing section in which the recipient is defined. Either this is named directly or the network path to be used is displayed. In the case of a simple P2P connection without additional participants, addressing can even be omitted. In the following cargo section, any amount of data bytes can be transferred from the source to the destination. The package is concluded with an end-of-packet (EOP). A new package can then be started.
When addressing in the path representation, the destination information corresponds to the navigation instruction of a navigation device from the car, for example when you are approaching a roundabout. Each router corresponds to a roundabout. Courtyard entrances or connections to other roundabouts can be connected to each such roundabout. The packet then receives a list of navigational instructions (e.g. "leave the next router via port 5"), which are ticked off one after the other. Specifically, every router has up to 31 such ports; the first address character in the incoming address field provides information on which port the message must use to leave the router. The outgoing address field is shortened accordingly by this first character (ticked off). The next router automatically receives the output port to be used by it as the first address character. The address field becomes shorter and shorter as the message travels and is ultimately empty for the recipient.
Web links
- Homepage
- ( Page no longer available , search in web archives: English operating instructions )