The JWST Integrated Science Instrument Module's command and data handling subsystem uses SpaceWire. This onboard networking standard links the subsystem with Webb's science instruments and supports the movement of commands, telemetry, and science data.
ISIM contains NIRCam, NIRSpec, MIRI, and the Fine Guidance Sensor, along with the electronics and computing needed to operate them. The ISIM Command and Data Handling system coordinates instrument activity, processes detector readouts, formats science data, and sends files toward the spacecraft's solid-state recorder.
SpaceWire was developed under the European Space Agency's leadership for spacecraft data networks. It is designed for relatively low-power, high-reliability links and can connect multiple instrument computers through a predictable packet-based architecture. Webb's version uses point-to-point SpaceWire interfaces between instrument electronics and the data-handling hardware.
A common mix-up is treating SpaceWire as Webb's long-distance radio link to Earth. It is not. Communications with ground stations use Webb's spacecraft communications system and NASA's Deep Space Network; SpaceWire handles internal onboard data exchange.