James Webb Space Telescope (JWST)

The James Webb Space Telescope (JWST) is;

Development of the JWST began in 1996 with a planned launch date of 2007 and a budget of US$500 million. There were many delays and cost overruns, including:

  • a major redesign in 2005,
  • a ripped sunshield during a practice deployment, this occurred following recommendations from an independent review board,
  • a threat by the U.S. Congress to cancel the project,
  • the COVID-19 pandemic.

The high-stakes nature of the launch and the telescope’s complexity were remarked upon by the media, scientists and engineers. Construction was completed in late 2016, followed by years of extensive testing before launch. The total project cost is now expected to be about US$9.7 billion.


The James Webb Space Telescope

  • has a mass about half of Hubble Space Telescope.
  • has a 6.5m diameter gold-coated beryllium primary mirror made up of 18 separate hexagonal mirrors.
  • mirror has a polished area of 26.3m2, of which 0.9m2is obscured by the secondary support struts, giving a total collecting area of 25.4m2. This is over six times larger than the collecting area of Hubble’s 2.4-meter diameter mirror. The mirror has a gold coating to provide infrared reflectivity and durability.
  • was initially designed for near-infrared astronomy, additionally it can also see orange and red visible light, as well as the mid-infrared region, depending on the instrument.
  • can sight objects up to 100 times dimmer than Hubble is able and objects much earlier in the history of the universe, back to redshift z≈20.
  • can additionally observe nearby objects, including objects in the Solar System, having an apparent angular rate of motion of 0.030 arc seconds per second or less. This includes all planets and satellites, comets, and asteroids beyond Earth’s orbit and most known Kuiper Belt Objects.
  • can watch opportunistic and unplanned targets within 48 hours of the a determination to do so, this may include supernovae and gamma ray bursts.

The design emphasises the near to mid-infrared for three reasons:

  • high-redshift (very early and distant) targets have their visible emissions shifted into the infrared and as such their light can only be observed today via infrared astronomy;
  • colder objects such as debris disks and planets emit most vigorously in the infrared;
  • these infrared bands are hard to study from the ground or by existing space telescopes such as Hubble.