Webb has two sides, divided by its sunshield: a hot side facing the Sun and Earth, and a cold side facing out into space, away from the Sun and Earth. The solar panels, communications antenna, navigation system, and electronic systems reside on the hot side facing the Sun and Earth. The mirrors and scientific instruments, which are very sensitive to infrared radiation, are housed on the cold side, where they are protected by the sunshield.
PRIMARY MIRROR: made up of 18 hexagonal segments that work together as a single, 6.5-meter mirror. The mirror segments are made of beryllium, a very lightweight and strong material. Each mirror segment is mounted on a hexapod with actuators that enable fine adjustments to each segment in six degrees of freedom: x and y position, piston, tip, tilt and clocking. An additional actuator at the center of each primary mirror segment provides radius of curvature control. This system enables controllers to finely time all 18 segments to work as one large mirror.
AFT-OPTICS SUBSYSTEM: contains the fixed tertiary mirror and the fine steering mirror. The Aft-Optics Subsystem's most prominent feature is a central baffle protruding from the center of the Primary mirror. This baffle prevents stray light from entering Webb's optics.
SECONDARY MIRROR: dissects the light from the primary mirror to where it can be controlled by Webb's instruments. The secondary mirror is moveable and can be adjusted to focus on the telescope.
INTEGRATED SCIENCE INSTRUMENT MODULE (ISIM): the structure that holds Webb's four science instruments.
SUNSHIELD: its five Kapton-based layers keep the infrared light (or heat) from the Sun, Earth and Moon, as well as the spacecraft bus electronics, from reaching Webb's mirrors and science instruments.
HIGH GAIN ANTENNA: Webb's main data antenna and means of communication between the spacecraft and controllers on Earth. Webb's science data and imagery is transmitted to Earth form this antenna.
SOLAR PANEL: converts sunlight into the power needed to operate the science instruments and the spacecrafts subsystems.
STAR TRACKERS: use guide stars for coarse pointing of the telescope. The star tracker data enables the alignment and control system to point the telescope so that the target appears in the field of views of the intended instrument. Once an observation is stared, the Fine Guidance Sensors (located in the ISIM with the instruments) can compensate for small drifts in the observatory's alignment and help the telescope maintain its good pointing.
SPACECRAFT BUS: provides the necessary support functions for the operation of the observatory. It contains six major spacecraft subsystems: Electrical Power Subsystem, Altitude Control Subsystem, Communication Subsystem, Command and Data Handing Subsystem, Propulsion Subsystem, and the Thermal Control Subsystem.
MOMENTUM TRIM TAB: balances the pressure exerted on Webb's sunshield by sunlight (photons). It works like a trim flap in sailing. The flap is not adjustable on orbit.
Credits
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STScI
