At one time it was one of the world’s premier observatories for astronomical research and instrument development at submillimeter wavelengths.

Now, 34 years after it achieved first light, the Caltech Submillimeter Observatory is in the final stages of fading into history, one of five telescopes marked for removal to make way for the planned Thirty Meter Telescope.

The observatory’s draft Site Decommissioning Plan was approved by the Maunakea Management Board this week, and Caltech officials said they’re aiming to have the final decommissioning plan approved by early 2022, allowing for the deconstruction and site restoration work to begin by summer 2022.

The plan describes the current condition of the site at the summit and offers details of how the facility will be removed and restored. At the end of the $4 million project, there should be no evidence that the telescope was even there, officials said.

The Caltech observatory is the first telescope on Mauna Kea to submit its site decommissioning plan for approval. The University of Hawaii Hoku Kea student teaching telescope is also making its way through the process.

“Caltech will continue to carefully consider community input as it seeks further approvals of the CSO decommissioning project,” Caltech physics professor and CSO Director Sunil Golwala said.

Caltech is one of the partner institutions planning to build the landmark Thirty Meter Telescope, the construction of which is on hold during the pandemic following five years of raging controversy. The project’s construction near the summit of Mauna Kea has been blocked in court and on the ground by Native Hawaiians who consider Hawaii’s tallest mountain sacred.

The submillimeter observatory was closed in 2015 following 30 years of “groundbreaking achievements,” according to Caltech. Numerous discoveries were accomplished there, and hundreds of students have used the facility, including more than 100 working on doctoral research projects. UH was one of the telescope’s partners.

Observations at the 10.4-meter radio telescope with a 60-foot dome led to the detection of heavy water on comets, which helped to determine the composition of comets, the university said. It also led to the observation of “dusty” planets, which optical telescopes often have trouble seeing.

As part of the decommissioning process, Caltech is writing an Environmental Assessment to evaluate the impacts of the decommissioning.

A draft EA — featuring an archaeological assessment, a cultural impact assessment, a hydrogeological evaluation and a biological inventory, among other studies — is expected to be available by summer and will be subject to a 30-day public comment period, officials said.

Caltech is responsible for the cost of the project.

The Maunakea Management Board is a panel of community volunteers that advises the University of Hawaii’s Office of Maunakea Management, which oversees the Maunakea Science Reserve.

A determination is expected to be made on the decommissioning of three other observatory sites by the end of 2025, according to UH.