The SpaceWire cable comprises four twisted pair wires with a separate shield around each twisted pair and an overall shield. To achieve a high data signalling rate with SpaceWire over distances up to 10 m a cable with the following characteristics is used:
- Characteristic impedance of 100 ohms differential impedance, which is matched to the line termination impedance.
- Low signal-signal skew between each signal in a differential pair and between Data and Strobe pairs.
- Low signal attenuation.
- Low cross-talk.
- Good EMC performance.
The structure of a SpaceWire cable is illustrated in Figure 23.
Figure 23 SpaceWire Cable Structure
One of the drawbacks of SpaceWire is the mass of the cable which is around 87 g/m. A new form of SpaceWire cable is currently being developed by ESA which is of significantly lower mass. This cable only uses one level of shielding.
SpaceWire is able to operate at 200 Mbits/s over 10 m cable. For longer distances it is possible to increase the wire gauge of the conductors to reduce cable attenuation.