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James Webb Space Telescope
Design

The Key Elements Of The Observatory

  • 6.5m class mirror, lightweight, deployable
  • Large sunshield enables passive cooling of telescope and instruments
  • Second Lagrange point (L2) orbit, with deployment during orbit insertion
  • Diffraction-limited imaging quality (Strehl = 0.8) for lambda = 2 micron
  • 0.6 - 28 micron wavelength range with zodiacal-light-limited imaging performance below 10 micron
  • Imaging and spectroscopic instrumentation over this wavelength range
  • 5 year required lifetime, 10 year goal
  • Risk mitigation by extensive testing
JWST top view

This Northrop Grumman SPIE article from Nov 2002 describes in more detail the selected architecture, its expected performance and the plans for integration and testing. Even though many details in the design have changed since the article was written, many of the design choices and procedures are still valid.

Instruments

NIRCam

Near Infrared Camera
  • Near-IR and visible camera
  • Sensitive over the 0.6-5 micron wavelength range
  • Two broad- and intermediate-band imaging modules, each with a 2.2 x 2.2 arcmin field of view
  • Each imaging module has two channels, with light split by a dichroic at ~2.35 micron
  • Short wavelength channel 0.0317" pixels, long wavelength channel 0.0648" pixels
  • Each module has coronagraphic capabilities

NIRCam Website

MIRI

Mid Infrared Instrument
  • Mid-IR camera and Integral Field Unit (IFU) and long-slit spectrograph
  • Sensitive over the 5-28 micron wavelength range
  • 1.88' x 1.27' field of view imaging, 12 filters
  • 3" x 3" IFU R=3000 spectrograph, in 5-10 and 10-27 micron channels
  • R=100 long-slit 5-10 micron spectrograph
  • Coronagraphic capabilities

MIRI Website

NIRSpec

NIRSpec
  • Multi-object dispersive spectrograph (MOS)
  • Sensitive over the 1-5 micron wavelength range
  • 3.4' x 3.4' field of view
  • ~0.1" pixels in the detector plane
  • R=1000 MOS Mode, 3 gratings cover 1.0-5.0 micron
  • R=2700 Integral Field Unit and Long-slit Modes
  • R=100 Prism, 0.6-5.0 mm in one exposure
  • Capable of observing more than 100 objects simultaneously using Multi-Shutter Assembly (developed by GSFC) with addressable 0.2 x 0.46 arcsec shutters

NIRSpec Website

NIRISS

NIRISS
  • Wide-field grism spectroscopy with R~150 between 1.0 – 2.5 microns
  • Single-object grism spectroscopy with R~700 between 0.6 – 3.0 microns
  • Interferometric imaging with a non-redundant aperture mask (NRM) between 3.8 - 4.8 microns
  • Broad-band imaging between 1.0 - 5.0 µm.
  • 2.2' X 2.2' Field of View

NIRISS Website

Guider

FGS

Find Guidance System
  • Find Guidance System
  • Enable stable pointing at the milli-arcsecond level
  • Sensitivity and field of view to allow guiding with 95% probability at any point on the sky (i.e. 95% at the galactic poles, better at most other places)
  • Provides guide-star centroids with ~ 7 mas precision at 16 Hz

FGS Website