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CALISTO, the Cryogenic Aperture Large Infrared Space Telescope Observatory, will enable extraordinarily high
sensitivity far-infrared continuum and moderate (R ~ 1000) resolution spectroscopic observations at wavelengths from
~30µm to ~300 μm - the wavelengths between those accessible by JWST and future ground based facilities.
CALISTO's observations will provide vital information about a wide range of important astronomical questions
including (1) the first stars and initial heavy element production in the universe; (2) structures in the universe traced by
H2 emission; (3) the evolution of galaxies and the star formation within them (4) the formation of planetary systems
through observations of protostellar and debris disks; (5) the outermost portions of our solar system through observations
of Trans-Neptunian Objects (TNOs) and the Oort cloud. With optics cooled to below 5 K, the photon fluctuations from
the astronomical background (Zodiacal, Galactic, and extragalactic) exceed those from the telescope. Detectors with a
noise equivalent power below that set by the background will make possible astronomical-background-limited sensitivity
through the submillimeter/far-infrared region. CALISTO builds on studies for the SAFIR (Single Aperture Far Infrared)
telescope mission, employing a 4m x 6m off-axis Gregorian telescope which has a simple deployment using an Atlas V
launch vehicle. The unblocked telescope with a cold stop has minimal sidelobes and scattering. The clean beam will
allow astronomical background limited observations over a large fraction of the sky, which is what is required to achieve
CALISTO's exciting science goals. The maximum angular resolution varies from 1.2" at 30 µm to 12" at 300 μm. The
5σ 1 hr detectable fluxes are ▵S(dν/ν = 1.0) = 2.2x10-20 Wm-2, and ▵S(dν/ν = 0.001) = 6.2x10-22 Wm-2. The 8 beams per
source confusion limit at 70 μm is estimated to be 5 μJy. We discuss CALISTO optics, performance, instrument
complement, and mission design, and give an overview of key science goals and required technology development to
enable this promising far IR/submm mission.
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