The SDSS-V Local Volume Mapper Survey Telescopes: from conception to science

This paper presents an overview of the SDSS-V Local Volume Mapper (LVM) telescope system. LVM is one of three surveys that form the fifth generation of the Sloan Digital Sky Survey, and it employs a coordinated network of four, 16-cm telescopes feeding three fiber spectrographs at the Las Campanas Observatory. The goal is to spectrally map more than 4000 square degrees of the Galactic plane with 37” spatial resolution and R~4000 spectral resolution over the wavelength range 360-980 nm. This corresponds to roughly 50 million individual spectra, which will reveal how distinct gaseous environments within our Galaxy interact with the stellar population, producing the large-scale interstellar medium that we observe. Accurately mapping and calibrating a substantial portion of the sky in this way requires a unique type of telescope. Each of the four units consists of a two-mirror siderostat in alt-alt configuration feeding an optical breadboard. This produces a fixed, stable focal plane for the fiber IFU and bundle. One telescope hosts the science IFU, while two others observe adjacent dark fields to calibrate geocoronal emission. The fourth telescope makes rapid observations of bright stars to compensate telluric absorption. The entrance slits of the spectrographs intersperse the fibers from all three types of telescope, producing truly simultaneous science and calibration exposures. After roughly four years of design, development, construction, testing, and commissioning, the LVM telescopes entered regular survey operations in late 2023. We summarize the entire LVM telescope project, from input scientific requirements to the actual performance achieved on-sky.