The JWST spacecraft bus provides the Observatory with electrical power, attitude control, thermal control, command and data handling, communications services, and propulsion.

• The solar array, together with the power conditioning, control and distribution systems, provide the electrical power needed for the mission, with a capacity of up to 3 kilowatts.
• The attitude control subsystem (ACS) provides attitude determination and control for all mission phases and modes of the observatory. The ACS interfaces with the Fine Guidance Sensor (FGS), located in the Integrated Science Instrument Module (ISIM), and with the telescope's fine steering mirror (FSM) for fine pointing control during observations.
• JWST's propulsion subsystem (comprised of chemical combustion thrusters and a propellant system) provides the means to correct the Observatory's orbit, control the observatory attitude in certain modes, and unload momentum stored in the reaction wheels. The observatory carries enough propellant for more than 20 years of science operations.
• The spacecraft Command & Data Handling (C&DH) subsystem supports command processing for the spacecraft bus, command routing to the ISIM and Optical Telescope Element (OTE), as well as telemetry recording and routing to the communications subsystem.
• The spacecraft's solid state recorder (SSR) provides about 65 Gbytes^† of storage for science data. The ISIM Command and Data Handling (ICDH) computer creates science data files as the detectors are read out, and transfers these files to the SSR where they are staged until they can be transmitted to the ground.  The SSR also stores engineering data generated by both ISIM and the spacecraft subsystems.
• The communications subsystem  supports communication with the DSN ground stations during both observations and slews. The subsystem has the capability to transmit to the ground a minimum of 229 Gbits of recorded science data and 8 Gbits of engineering data during a 4-hour contact, while concurrently transmitting real-time telemetry. The DSN provides an average of 10 hours of contact daily, usually divided into two to three separate contacts. Playback and download of the recorder data occurs automatically whether during attended or unattended contacts.