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SAFIR Telescope

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SAFIR will bridge the critical gap between the two fundamentally different types of astronomical facilities. On the short wavelength side, we will have the JWST observing in the near-IR and using the same basic principles as the Hubble Space Telescope. The sensitivity of the JWST, however will be limited for wavelengths beyond about 20 microns (0.02 mm), because the telescope is passively cooled to only 45 K.

On the long-wavlength side of SAFIR's range, the ground-based Atacama Large Millimeter Array (ALMA) will be astronomers' primary tool for wavelengths beyond about 1 mm. ALMA will be a very powerful array of 64 telescopes, and will use the heterodyne receiver techniques of radio astronomy. As such, its sensitivity at wavelengths less than about 1 mm will be limited by the relative roughness of its mirror surfaces, performance of the receivers, and atmospheric transmission.

In SAFIR's spectral regime of 20 microns to 1 mm, the fundamental limit imposed by the astrophysical background allows more than 1000 times better sensitivity than the currently planned US and European missions as shown in the figure below.
Spectral capability in the FAR-IR
Spectral capability in the FAR-IR

Unlike in the optical, there is a huge sensitivity gain possible with a cold telescope. And unlike at millimeter wavelengths, a single large mirror provides sufficient light collecting area for observations at great distances, into the early universe. Together, the resulting increase in astronomical capability is tremendous, especially when compared with the relatively small incremental technology costs after the JWST and TPF are built.

To put SAFIR's sensitivity into perspective, suppose you turned on a small flashlight, powered by two AA batteries, sealed it inside a basketball, and launched it into the frigid depths of space. The little light bulb would raise the temperature of the ball's surface to 115 Kelvin (115 degrees Celsius above absolute zero, or around -253 F), and this tiny amount of heat would radiate at far-infrared wavelengths. SAFIR would be able to detect it at a distance of nearly four million miles, or 15 times the distance to the moon.

While other systems such as the JWST might be capable of detecting the visible light from a small flashlight at 4 million miles, they could not detect the energy from the flashlight if it were shrouded inside a basketball, because those telescopes are not sensitive to the far-IR wavelengths at which the cold basketball would radiate.

In the same way, SAFIR's long-wavelength sensitivity is critical for observations of dust-enshrouded formation of stars, planets, and entire galaxies.

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