page_title: Optical Telescope Element
hierarchical_section_title: Optical Telescope Element
caption_attribution_description: English: Engineers in a clean room, using CO2 snow to clean a gold-coated test mirror for the James Webb Space Telescope
context_page_description: Optical Telescope Element is a sub-section of the James Webb Space Telescope, a large infrared space telescope scheduled to be launched early 2021. The OTE consists of some major parts of the telescopes including the main mirror, the secondary mirrors, the framework and controls to support those mirrors, and various thermal and other systems to support the functioning of the telescope. The other two major sections of the JWST are the Integrated Science Instrument Module and the Spacecraft Element, which includes the Spacecraft Bus and Sunshield. The OTE collects the light and sends it to the science instruments in the ISIM. The OTE has been compared to being the "eye" of the telescope and the backplane of it to being the "spine".
  The primary mirror is a tiled assembly of 18 hexagonal elements, each 1.32 meters from flat to flat. This combination yields an effective aperture of 6.5 meters and a total collecting surface of 27 square meters. Secondary mirrors complete the f/20 anastigmatic imaging optics. The complete system provides an effective f/number of f/16.67 and focal length of 131.4 meters.
context_section_description: Optical Telescope Element (OTE) is a sub-section of the James Webb Space Telescope, a large infrared space telescope scheduled to be launched early 2021. The OTE consists of some major parts of the telescopes including the main mirror, the secondary mirrors, the framework and controls to support those mirrors, and various thermal and other systems to support the functioning of the telescope. The other two major sections of the JWST are the Integrated Science Instrument Module (ISIM) and the Spacecraft Element (SE), which includes the Spacecraft Bus and Sunshield. The OTE collects the light and sends it to the science instruments in the ISIM. The OTE has been compared to being the "eye" of the telescope and the backplane of it to being the "spine".
  The primary mirror is a tiled assembly of 18 hexagonal elements, each 1.32 meters from flat to flat. This combination yields an effective aperture of 6.5 meters and a total collecting surface of 27 square meters. Secondary mirrors complete the f/20 anastigmatic imaging optics. The complete system provides an effective f/number of f/16.67 and focal length of 131.4 meters. The main three-mirror telescope is a Korsch-type design,  and it feeds into the Aft Optics Subsystem (part of OTE), which in turn feeds into the Integrated Science Instrument Module which holds the science instruments and fine guidance sensor.
caption: The secondary mirror being cleaned with carbon dioxide snow
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