On April 14, the Dark Energy Spectroscopic Instrument (DESI) completed its survey of the sky. Finished ahead of its planned five-year timeline, the project produced a 3D map of the universe using data from 47 million galaxies and quasars, along with more than 20 million nearby stars. DESI has proven immensely successful—surpassing its original science goals and recently earning the Lancelot M. Berkeley–New York Community Trust Prize for Meritorious Work in Astronomy. While the ground-based survey is now globally recognized, its origins trace back to a proposed space-based mission at the Space Sciences Laboratory (SSL).
The SuperNova/Acceleration Probe (SNAP) Telescope was proposed in 2004 by Michael J. Sholl, then an optical engineer at SSL. SNAP was envisioned as an Earth-orbiting satellite designed to map supernovae and study cosmic expansion as part of a broader dark energy survey, but a key innovation ultimately eliminated the need for a space-based platform. Sholl designed a wide-field prime focus corrector capable of delivering a 3.2-degree field of view on a 4-meter telescope. Incoming light is directed through six lenses onto a one-meter focal plane, maintaining uniform magnification across the image. This breakthrough made a ground-based survey not only viable, but highly effective.
Further technical development at SSL focused on DESI’s fiber-optic system. The instrument’s focal plane is served by 5,000 glass fibers, each 47.5 meters long and roughly the width of a human hair. Because components needed to be manufactured and integrated in parallel, the fibers needed to be spliced. Conventional splicing methods, introduce unacceptable signal loss and optical degradation—critical issues when detecting faint light from galaxies emitted over 10 billion years ago. Claire Poppett and Jerry Edelstein, both research physicists at SSL, overcame this challenge by developing a novel splicing technique that reduces signal degradation to nearly zero in lab settings. These fibers feed into DESI’s ten spectrographs, which were designed by Michael Lampton and Patrick Jelinsky.
Many core components of DESI were constructed at Lawrence Berkeley National Laboratory, located just down the hill from SSL. The instrument was then integrated into the Mayall 4-Meter Telescope at Kitt Peak National Observatory. Originally built in the early 1970s, the telescope has been transformed into a cutting-edge astronomical facility through DESI.
“Before DESI, most researchers doubted that a redshift survey on this scale could be carried out from the ground—but engineers at the Space Sciences Laboratory made it happen,” said Poppett.
Read more about the completion of the DESI survey.