The information above on pixel sizes for different space telescopes is summarized in table 2 below. The shorter wave channel would cover the range 200–1000 nm with resolution 0.003 arcsec/pixel, and a near-infrared (NIR) channel will image over the range 1000–2500 nm at 0.008 arcsec/pixel. As for both HST and JWST, the different instruments would each be apportioned a small fixed 2 × 3 arcmin region of the telescope's field of view. LUVOIR A, with 15 m aperture, would be placed in a similar orbit in L2 as JWST. The total field of view observed simultaneously by all the JWST instruments is 25 square arcmin.Ī concept for a larger successor to HST and JWST now being developed by NASA, for launch in the late 2030s, is the Large Ultraviolet Optical Infrared Surveyor. JWST provides also for simultaneous spectroscopy over the same waveband of 100 objects, selected by micro-shutters from a 9 square arcmin field of view. For the shorter waveband 0.6–2.5 µm, the plate scale is chosen for a pixel resolution of 0.032 arcsec per pixel. Both cameras use a 16-megapixel HgCdTe array with the same 18 µm pixel size as the HST. Thus, separate infrared cameras image in different wavebands, each sampling a separate 2.2′ × 2.2′ field. The JWST instruments, like those of the HST, will each be allocated a small fixed section of the telescope's field of view. It is not designed to be serviced, and has a projected lifetime of 10 years, set by the expenditure of fuel to stay on orbit. The telescope is configured for observations into the thermal infrared with a thermal shield for radiative cooling to an operating temperature of 40 K. The 6.5 m James Webb Space Telescope (JWST), currently scheduled for launch in 2021, will be in a distant orbit at L2, as will Roman and Euclid. Wide-field imaging from space will be provided also by Euclid, set for launch in 2022, with 1.2-m aperture, and a 0.5 square degree field of view imaged by large CCD and HgCdTe imaging array detectors with, respectively, 0.1′′ and 0.3′′ pixels. Its much larger 0.28 square degree field of view is to be imaged by HgCdTe arrays with 0.11 arcsec pixels, providing resolution and sensitivity in the near infrared like that of WFC3/IR. The Roman Space Telescope (formerly WFIRST) is a second 2.4-m telescope set for launch in 2025. The high resolution of the Extreme Deep Field, with FWHM close to the pixel sampling size, was obtained by sub-pixel image drizzling or dithering. Here, the 15 µm CCD pixels provide 0.05 arcsec pixel sampling. The shorter wavelength images were recorded over a 2.2 arcmin square field of view with the ACS camera, using a 16-megapixel silicon CCD array at f/26. Matched to this field at f/11, the HgCdTe detector with 18 µm pixels provided 0.12 arcsec pixel sampling. This was used to obtain infrared images over a 2.0 × 2.3 arcmin field of view, a size set by the telescope architecture which allocates different sections of the field of the same size to different instrument slots. These new instruments took advantage of detector technology advances made since the launch of the telescope, for example, the 1-megapixel HgCdTe imaging sensor used in WFC3/IR. The small square is 1.6 arcsec on a side. This article is part of a discussion meeting issue ‘Astronomy from the Moon: the next decades’.ĭetail from the HST Extreme Deep Field. Cooling to less than 100E K would be achieved with a surrounding cylindrical thermal shield. The lunar site would allow also for the installation of new instruments to keep up with evolving scientific priorities and advancing technology. While this telescope could be built for operation in free space, a site accessible to a human outpost at the Moon's south pole would be advantageous, for assembly and repairs. Direct imaging and spectroscopy of exoplanets can take advantage of the un-aberrated, on-axis image (5 nm RMS wavefront error). A multi-object spectrograph with 10 000 fibres will allow spectroscopy with 0.02 arcsec resolution. ![]() The initial instrument complement includes a 400 gigapixel silicon imager with 2 µm pixels (0.005 arcsec), and a 60 gigapixel HgCdTe imager with 5 µm pixels (0.012 arcsec). Several carousel-mounted instruments can each access directly the full image. ![]() ![]() The optical system yielding a 1°, 1.36 m diameter image at f/3.9 has relatively small central obscuration, 9% by area on axis, and is fully baffled. Its diffraction-limited images are a hundred times sharper than from wide-field ground-based telescopes and extend over much if not all the field, 40 arcmin diameter at 500 nm wavelength, for example. A 20 m space telescope is described with an unvignetted 1° field of view-a hundred times larger in area than fields of existing space telescopes.
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