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James Webb Space Telescope (JWST)



The James Webb Space Telescope (JWST) is a large infrared (IR) optimized space observatory designed to study the earliest phases of the universe, how galaxies formed, how stars and protoplanetary systems develop, and to observe planets in our own and other solar systems. JWST is scheduled to launch on 31 October 2021 into an orbit about the second Earth-Sun LaGrange point (L2), and is planned to operate for 10 years. The telescope has a 6.6 meter diameter aperture and carries four primary science instruments: a Near-IR Camera (NIRCam), a Near-IR Spectrograph (NIRSpec), a near_IR Tunable Filter Imager (TFI) and a Mid-IR Instrument (MIRI). The near-IR instruments operate in the wavelength range from 0.6 to 5.0 microns, the mid-IR instrument covers 5.0 to 29 microns.

Spacecraft and Subsystems

Total mass of JWST is 6500 kg, including the station-keeping propellant. The primary mirror of JWST is made up of 18 hexagonal gold-coated beryllium segments, 1.32 meters wide (flat-to-flat) that fit together to form the 6.6 meter wide (flat-to-flat) mirror surface. There is no mirror in the center. The segments are folded for launch, and are independently moveable. The mirror has a 25 square meter collecting area, it has an effective f/number of 20 and an effective focal length of 131.4 m. A secondary mirror is mounted on three struts above the reflecting surface of the main mirror. The aft optical subsystem, which includes a glare stop, tertiary mirror, and fine steering mirror, is mounted at the center of the main mirror.

The primary mirror is supported by a backplane, which holds the mirror segments and segment motors. The Integrated science module, containing the instruments, support electronics, and cryocoolers, is mounted behind the telescope. The entire telescope assembly is mounted on a large (roughly 10 x 22 meters), multilayer sunshield, which always keeps the telescope in shade so that it can operate at the cold temperatures necessary for IR observations. Cryocoolers are used to further lower the temperatures. The spacecraft bus is mounted on the bottom (sunward) side, and contains the steering and control mechanisms, star trackers, computers, communications, dish antenna, and solar panels.

Mission Profile

JWST is scheduled to launch on 18 December 2021 from launch site ELA-3 in Kourou, French Guiana. Launch will take place on an Ariane 5 Enhanced Capability-A rocket. It will be placed in a 6 month orbit about the Earth-Sun Lagrange 2 (L2) point, in a plane inclined slightly to the ecliptic plane. The sunshade will be deployed 2 days after launch and the primary mirror deployment will begin 4 days after launch. The L2 point is about 1.5 million km from Earth, the spacecraft will reach it in about a month, begin commissioning at 113 days after launch, and will complete commissioning and begin observations 6 months after launch. The station-keeping propellant is expected to last for 10 years.

Image credit: Northrup-Grumman

Alternate Names

    Facts in Brief

    Launch Date: 2021-12-18
    Launch Vehicle: Ariane 5
    Launch Site: Kourou, French Guiana
    Mass: 6500 kg

    Funding Agency

    • National Aeronautics and Space Administration (United States)


    • Planetary Science
    • Astronomy

    Additional Information

    Questions and comments about this spacecraft can be directed to: Dr. David R. Williams



    NameRoleOriginal AffiliationE-mail
    Dr. Hashima HasanProgram ScientistNASA
    Dr. John C. MatherProject ScientistNASA Goddard Space Flight
    Dr. Jonathan P. GardnerDeputy Project ScientistNASA Goddard Space Flight
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