Over its 5-year observing lifetime, DESI will measure the spectra of more than 30 million galaxies and quasars covering 14,000 square degrees. The DESI instrument will provide unprecedented multi-object spectroscopy incorporating a novel design.
DESI will have new corrector optics that provide a 3-degree-diameter field of view that feeds a focal plate containing of 5,000 robotic positioners. The positiners can be reconfigured within 3 minutes to measure the spectra of a new set of galaxies. Optical fibers mounted to the positioners will extend 50 meters down the telescope to feed 10 broad-band spectrographs, each containing three detectors. The spectrographs will cover a spectral range of 360 nanometers (nm) to 980 nm with a resolution of 2,000 to 5,000, enabling DESI to probe redshifts up to 1.7 for emission line galaxies and 3.5 for the lyman-α spectra from quasars.
The instrument will be mounted on the 4-meter Mayall Telescope in 2018. The instrument is being built by several institutions and will be integrated after delivery to the telescope.