Xuntian

Xuntian (Chinese: 巡天; pinyin: Xúntiān), also known as the Chinese Survey Space Telescope (CSST) (Chinese: 巡天空间望远镜; pinyin: Xúntiān Kōngjiān Wàngyuǎnjìng) is a planned Chinese space telescope currently under development. It will feature a 2-meter (6.6 foot) diameter primary mirror and is expected to have a field of view 300–350 times larger than the Hubble Space Telescope. This will allow the telescope to image up to 40 percent of the sky using its 2.5 gigapixel camera over ten years.

Xuntian is scheduled for launch in 2025 on a Long March 5B rocket to co-orbit with the Tiangong space station in slightly different orbital phases, which will allow for periodic docking with the station.

This state-of-the-art telescope, characterized by its off-axis design without any obstruction, sidesteps diffraction challenges associated with mirror support structures. As a result, its point spread function (PSF) remains unscathed, presenting a valuable asset for weak-lensing shear measurements. The CSST is equipped with five first-generation instruments, including a survey camera, a terahertz receiver, a multichannel imager, an integral field spectrograph, and a cool planet imaging coronagraph.

The primary mission of the CSST revolves around high-resolution large-area multiband imaging and slitless spectroscopy surveys, spanning the wavelength range of 255–1,000 nm. Precise cosmology serves as the principal scientific driver behind this ambitious endeavor, with a focus on observing regions at median-to-high Galactic and ecliptic latitudes. Over a period of 10 years, the survey camera is slated to cover approximately 17,500 square degrees of the sky in various bands, reaching point-source 5σ limiting magnitudes of about 26 (AB mag) in g and r bands.

The CSST's spectral resolution (R=λ/Δλ) for the slitless spectrograph averages no less than 200, attaining wide-band-equivalent limiting magnitudes in GV (400–620 nm) and GI (620–1,000 nm) bands at about 23 mag. Beyond its wide-area survey, the CSST will target specific deep fields, aiming for observations that surpass the depth of the broader survey by at least one magnitude. The collective strengths of its angular resolution, depth, wavelength range, and capacity for both imaging and spectroscopy, coupled with extensive sky coverage, render the CSST survey highly competitive.

Notably, the CSST's observations are poised to complement and enhance other contemporaneous large-scale projects, including the Vera Rubin Observatory, Euclid, and the Nancy Roman Space Telescope. Together, these initiatives promise to yield unprecedented datasets that hold the potential for groundbreaking discoveries spanning the realms from our solar system to cosmology and beyond.