page_title: James Webb Space Telescope
section_title: Construction
hierarchical_section_title: James Webb Space Telescope / History / Construction
caption_attribution_description: English: Caption: During cryogenic testing, the mirrors will be subjected to temperatures dipping to -415 degrees Fahrenheit, permitting engineers to measure in extreme detail how the shape of each mirror changes as it cools. More information: http://www.nasa.gov/centers/marshall/news/news/releases/2010/10-094.html
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: In January 2007, nine of the ten technology development items in the project successfully passed a non-advocate review. These technologies were deemed sufficiently mature to retire significant risks in the project. The remaining technology development item (the MIRI cryocooler) completed its technology maturation milestone in April 2007. This technology review represented the beginning step in the process that ultimately moved the project into its detailed design phase (Phase C). By May 2007, costs were still on target. In March 2008, the project successfully completed its Preliminary Design Review (PDR). In April 2008, the project passed the Non-Advocate Review. Other passed reviews include the Integrated Science Instrument Module review in March 2009, the Optical Telescope Element review completed in October 2009, and the Sunshield review completed in January 2010.
  In April 2010, the telescope passed the technical portion of its Mission Critical Design Review (MCDR). Passing the MCDR signified the integrated observatory can meet all science and engineering requirements for its mission. The MCDR encompassed all previous design reviews. The project schedule underwent review during the months following the MCDR, in a process called the Independent Comprehensive Review Panel, which led to a re-plan of the mission aiming for a 2015 launch, but as late as 2018. By 2010, cost over-runs were impacting other projects, though JWST itself remained on schedule.
  By 2011, the JWST project was in the final design and fabrication phase (Phase C). As is typical for a complex design that cannot be changed once launched, there are detailed reviews of every portion of design, construction, and proposed operation. New technological frontiers have been pioneered by the project, and it has passed its design reviews. In the 1990s it was unknown if a telescope so large and low mass was possible.
  Assembly of the hexagonal segments of the primary mirror, which was done via robotic arm, began in November 2015 and was completed in February 2016. Final construction of the Webb telescope was completed in November 2016, after which extensive testing procedures began. In March 2018, NASA delayed the JWST's launch an additional year to May 2020 after the telescope's sunshield ripped during a practice deployment and the sunshield's cables did not sufficiently tighten. In June 2018, NASA delayed the JWST's launch an additional 10 months to March 2021, based on the assessment of the independent review board convened after the failed March 2018 test deployment. The review also found JWST had 344 potential single-point failures, any of which could doom the project. In August 2019, the mechanical integration of the telescope was completed, something that was scheduled to be done 12 years before in 2007. Following this, engineers now are working to add a five layer sunshield in place to prevent damage to telescope parts from infrared rays of the Sun.
caption: Mirror segments undergoing cryogenic tests at the X-ray & Cryogenic Facility at Marshall Space Flight Center
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