JWST 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

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-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

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

MIRI

• 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

FGS

• Fine 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)
• Tunable Filter Imager has one 2.2 x 2.2 arcmin field of view and selectable R~100 between 1.5-5.0 microns