Caltech Submillimeter Observatory Decommissioning Updates
CSO on Maunakea
California Institute of Technology’s (Caltech) draft Site Decommissioning Plan (SDP) to remove the Caltech Submillimeter Observatory (CSO) and restore the site was unanimously approved by the Maunakea Management Board (MKMB) on March 2, 2021.

MKMB is a board of community volunteers that advises the University of Hawai‘i’s Office of Maunakea Management, which oversees the Maunakea Science Reserve.

CSO is one of the first two observatories on the mountain to undertake the decommissioning process, along with the University of Hawai‘i Hoku‘kea telescope. CSO is the first to submit its SDP for review.

Caltech’s next planning steps are the Draft Environmental Assessment (EA), which is currently under review, and the Conservation District Use Application (CDUA).

The EA and CDUA will go to MKMB and the public for comment. Then, with the Site Decommissioning Plan (SDP) attached, they will be submitted the state Department of Land and Natural Resources. If all goes smoothly, Caltech anticipates DLNR will hold a hearing, with public comment period, later this year. Caltech will also host three public workshops toward the end of 2021. Caltech hopes to have its plans approved by early 2022, which would enable the physical deconstruction and restoration to begin by summer 2022.

CSO's 10.4-meter radio telescope went online in 1987 for research by astronomers at Caltech and other institutions, including more than 200 students. Operations at the observatory ended in 2015.

“It was Caltech’s privilege to operate CSO on Maunakea and an honor to continue our relationship with the mauna and its people through this decommissioning effort and Caltech’s participation in other astronomy projects,” Caltech physics professor and CSO Director Sunil Golwala said.

For additional information please visit

The Thirty Meter Telescope (TMT) Project has been developed as collaboration among Caltech, the University of California (UC), the Association of Canadian Universities for Research in Astronomy (ACURA), and the national institutes of Japan, China, and India with the goal to design, develop, construct, and operate a thirty-meter class telescope and observatory on Maunakea in cooperation with the University of Hawaii (TMT Project). The TMT International Observatory LLC (TIO), a non-profit organization, was established in May 2014 to carry out the construction and operation phases of the TMT Project. The Members of TIO are Caltech, UC, the National Institutes of Natural Sciences of Japan, the National Astronomical Observatories of the Chinese Academy of Sciences, the Department of Science and Technology of India, and the National Research Council (Canada); the Association of Universities for Research in Astronomy (AURA) is a TIO Associate. Major funding has been provided by the Gordon & Betty Moore Foundation.

For more information about the TMT project, visit, or follow @TMTHawaii.
Sandra Dawson
TMT Manager, Hawaii Community Affairs
 111 Nowelo Street,
Hilo, HI 96720
Phone (808) 284-9922