The first two of five Mauna Kea telescopes planned to be decommissioned in exchange for development of the Thirty Meter Telescope are scheduled to be removed from the mountain by 2023, according to the latest plan outlined by officials with the University of Hawaii.

The plan pushes back the targeted decommissioning deadline for the telescopes that was described in a resolution of the UH Board of Regents in November.

According to that resolution, the Caltech Submillimeter Observatory and the UH-Hilo Hoku Kea teaching telescope were to be removed no later than Dec. 31, 2021.

But while progress has been made in the extensive decommissioning process, the effort is going to take longer on both accounts, said Greg Chun, UH executive director of Mauna Kea stewardship.

Meanwhile, the fate of the TMT continues to be murky as the $1.4 billion-plus pro­ject has been stalled by legal and regulatory hurdles and protests over the last five years.

Although the current truce between the TMT and its opponents is tentatively set to conclude at the end of the month, the international consortium planning to develop the next-generation telescope has indicated it has no immediate plans to start construction and the ki‘ai “protectors” have vowed to once again guard Mauna Kea Access Road against construction vehicles.

Chun said the deconstruction and site restoration work for the Caltech observatory is set to begin next year and be completed by late 2022.

The project, expected to be paid for by Caltech, will include the removal of the dome, outbuildings and related infrastructure along with the restoration of the site. The astronomical instruments have already been removed from the observatory.

A draft environmental assessment under review by Caltech is expected to include technical surveys such as an environmental site study and hazardous materials evaluation.

The Hoku Kea’s deconstruction and site restoration is scheduled to begin in early 2023 and take about six months, Chun said.

On Feb. 18 the Maunakea Management Board approved UH-Hilo’s formal notice of intent to decommission the telescope on the condition that the university proceed with planning and permitting for a replacement telescope.

The process would include identifying a new location, possibly the Hale Pohaku mid-level facilities on Mauna Kea, he said.

Chun said the university is in the process of awarding a contract to identify a location and begin planning for the new teaching telescope, a facility that would be smaller than other telescopes at the summit.

According to November’s resolution, a determination would be made on the decommissioning of the remaining three observatory sites on or by Dec. 30, 2025.

Removing five current telescopes is a condition of the TMT’s conservation district use permit. Construction of the 18 story-tall telescope itself is expected to take at least 10 years.