page_title: James Webb Space Telescope
section_title: Spacecraft Bus
hierarchical_section_title: James Webb Space Telescope / Features / Spacecraft Bus
caption_attribution_description: English: The spacecraft bus provides the necessary support functions for the operation of the Webb Observatory. At left is a top view of the bus.Italiano: Modello a blocchi della navicella del JWST
context_page_description: The James Webb Space Telescope is a space telescope that is planned to succeed the Hubble Space Telescope as NASA's flagship astrophysics mission. The JWST will provide improved infrared resolution and sensitivity over Hubble, and will enable a broad range of investigations across the fields of astronomy and cosmology, including observing some of the most distant events and objects in the universe, such as the formation of the first galaxies.
  The primary mirror of the JWST, the Optical Telescope Element, is composed of eighteen 1.32-metre hexagonal mirror segments made of gold-plated beryllium which combine to create a 6.5-metre diameter mirror that is considerably larger than the Hubble's 2.4-metre mirror. Unlike the Hubble, which observes in the near ultraviolet, visible, and near infrared spectra, the JWST will observe in a lower frequency range, from long-wavelength visible light through mid-infrared, which will allow it to observe high redshift objects that are too old and too distant for the Hubble to observe.
context_section_description: The Spacecraft Bus is the primary support component of the James Webb Space Telescope, that hosts a multitude of computing, communication, propulsion, and structural parts, bringing the different parts of the telescope together. Along with the Sunshield, it forms the spacecraft element of the space telescope. The other two major elements of the JWST are the Integrated Science Instrument Module (ISIM) and the Optical Telescope Element (OTE). Region 3 of ISIM is also inside the Spacecraft Bus; region 3 includes ISIM Command and Data Handling subsystem and the MIRI cryocooler.
  The Spacecraft Bus is connected to Optical Telescope Element via the Deployable Tower Assembly, which also connects to the sunshield.
  The structure of the Spacecraft Bus must support the 6.5-ton space telescope, while it itself weighs 350 kg (about 770 lb). It is made primarily of graphite composite material. It was assembled in California by 2015, and after that it had to be integrated with the rest of the space telescope leading up to its planned 2021 launch. The bus can provide pointing of one-arcsecond and isolates vibration down to two milliarcseconds.
  The Spacecraft Bus is on the Sun-facing "warm" side and operates at a temperature of about 300 K. Everything on the Sun facing side must be able to handle the thermal conditions of JWST's halo orbit, which has one side in continuous sunlight and the other in the shade of the spacecraft sunshield.
  Another important aspect of the Spacecraft Bus is the central computing, memory storage, and communications equipment. The processor and software direct data to and from the instruments, to the solid-state memory core, and to the radio system which can send data back to Earth and receive commands. The computer also controls the pointing and moment of the spacecraft, taking in sensor data from the gyroscopes and star tracker, and sending the necessary commands to the reaction wheels or thrusters depending.
caption: Diagram of the Spacecraft Bus. The solar panel is in green and the light purple flats are radiators shades.
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