The James Webb Space Telescope (JWST or Webb; an early name was Next Generation Space Telescope, i.e., NGST) is a 6.5 meter (21 ft) NASA/European Space Agency/CSA space-based infrared telescope under construction, planned for launch in October 31, 2021 (the launch date has been delayed several times), and deployed at the Earth-Sun L2 Lagrangian point. Its lifetime will be limited by the fuel it carries for stationkeeping (maintaining its orbit). A five-and-a-half-year program is targeted and a ten-year life is hoped for. Infrared was chosen because it is necessary for viewing very distant, redshifted astronomical objects (distant galaxies and quasars) and Earth atmosphere limits infrared observation from the ground. Infrared is also useful for observation of nearer objects as well: it is virtually always present in thermal emission. Instruments:
One observation target is spectroscopy of extra-solar planets. NIRISS can operate in a mode termed SOSS, for single-object slitless spectroscopy, aimed at differential spectroscopy for observing the light curves of transiting exoplanets. MIRI offers medium-resolution (MRS mode, offering resolutions of 1500-3500) which is hoped to done with direct imaging of exoplanets. NIRSpec offers several gratings, with grating labeled G395 offering a spectral resolution of as high as 2700. NIRCam offers WFSS (wide field slitless spectroscopy) mode. JWST also offers aperture masking interferometry (AMI). Established classes of JWST observing programs include:
Among the GTO programs is NEAT (NIRISS Exploration of the Atmospheric diversity of Transiting exoplanets).