The Observatory is the space-based portion of the James Webb Space Telescope system. It is comprised of the Optical Telescope Element (OTE), the Integrated Science Instrument Module (ISIM), the sunshield and the spacecraft bus.

The OTE is the eye of the Observatory. It consists of the mirrors and the backplane. The OTE gathers the light coming from space and provides it to the science instruments located in the ISIM. The backplane is like the "spine" of Webb. It supports the mirrors.

The ISIM contains Webb's cameras and instruments. It integrates four major instruments and numerous subsystems into one payload.

The sunshield separates the observatory into a warm sun-facing side (spacecraft bus) and a cold anti-sun side (OTE and ISIM). The sunshield keeps the heat of the Sun, Earth, and spacecraft bus electronics away from the OTE and ISIM so that these pieces of the Observatory can be kept very cold (The operating temperature has to be kept under 50 K or -370 deg F).

The spacecraft bus provides the support functions for the operation of the Observatory. The bus houses the six major subsystems needed to operate the spacecraft: the Electrical Power Subsystem, the Attitude Control Subsystem, the Communication Subsystem, the Command and Data Handling Subsystem, the Propulsion Subsystem, and the Thermal Control Subsystem.

A Breakdown of Observatory Elements

The Observatory consists of:

• The Optical Telescope Element (OTE) includes:
  • the mirrors
  • the backplane
• The Integrated Science Instrument Module (ISIM) contains these instruments:
  • Mid-Infrared Instrument (MIRI)
    
  • Near-Infrared Spectrograph (NIRSpec)
    
  • Near-Infrared Camera (NIRCam)
    
  • Fine Guidance Sensor/ Near InfraRed Imager and Slitless Spectrograph (FGS-NIRISS)
• Sunshield
• Spacecraft Bus
• Other elements include:
  • The momentum flap balances the solar pressure on the sunshield, like a trim flap in sailing. It's not adjustable on orbit, but it is while it's on the ground.
  • The Earth-pointing antenna sends science data back to earth and receives commands from NASA's Deep Space Network.
  • The solar array is always facing the sun to convert sunlight to electricity to power the Observatory.
  • The star trackers are small telescopes that use star patterns to target the observatory.