Dark Energy Spectroscopic Instrument

Lore & Background

DESI received a go-ahead to start R&D for the project in December 2012 with the assignment of the Lawrence Berkeley National Laboratory as the managing laboratory. Dr. Michael Levi, a senior scientist at the Lawrence Berkeley National Laboratory, was appointed by the laboratory to be DESI's project director, serving from 2012 throughout construction. The U.S. Department of Energy approved CD-0 (Mission Need) on September 18, 2012, CD-1 (Alternative Selection and Cost Range) on March 19, 2015, and CD-2 (Performance Baseline) on September 17, 2015. U.S. Congressional approval for the start of DESI as a new Major Item of Equipment was provided in the Fiscal Year 2015 Energy & Water appropriations legislation. Construction started June 22, 2016 with CD-3 approval and was largely assembled by 2019, with commissioning finishing on March 21, 2020, marking the formal end of the project (CD-4). DESI was completed under budget by $1.9M and 17 months ahead of schedule, receiving the DOE Project Management Excellence Award for 2020. After a pause for the pandemic and a transition to remote operations, DESI returned to survey operations in December 2020, with a final checkout and validation phase prior to starting its planned five-year survey on May 14, 2021. DESI was shut down for three months in the summer of 2022 due to the Contreras fire which engulfed Kitt Peak, but was undamaged and is acquiring scientific data.

Reader's Guide

DESI is notable for its role in probing the expansion history and large-scale structure of the universe, a key prediction of cosmological models. Its observations permit scientists to probe various aspects of cosmology, including dark energy, alternatives to general relativity, neutrino masses, and the primordial universe. The data from DESI are used to create three-dimensional maps of the distribution of matter covering an unprecedented volume of the universe with unparalleled detail, providing insight into the nature of dark energy and establishing whether cosmic acceleration is due to a cosmic-scale modification of General Relativity. DESI measures the expansion history using baryon acoustic oscillations (BAO) imprinted in the clustering of galaxies, quasars, and the intergalactic medium. The BAO technique was identified in the 2006 Dark Energy Task Force report as a key method for studying dark energy. In May 2014, the High-Energy Physics Advisory Panel endorsed DESI. In March 2025, the DESI collaboration released Data Release 1 (DR1), containing spectra and redshifts for 18.7 million objects observed during the first 13 months of the main survey, making it the largest spectroscopic redshift dataset released at the time. Analysis of DESI's first three years of cosmological data, published in 2025, strengthened evidence that dark energy may evolve over cosmic time rather than behaving as a constant cosmological constant. In 2026, DESI completed its five-year primary survey after mapping more than 47 million galaxies and quasars, exceeding its original design goals.

Did You Know?

• DESI's focal plane accommodates 5,000 small robotic fiber positioners on a 10.4 millimeter pitch, and the entire focal plane can be reconfigured in less than two minutes.
• The DESI instrument is capable of taking 5,000 simultaneous spectra over a wavelength range from 360 nm to 980 nm.