Mauna Kea, a mountain on the island of Hawaii, is home to more than a dozen astronomical observatories.Credit: Julie Thurston

Construction of the controversial Thirty Meter Telescope (TMT) is set to resume in Hawaii on 15 July after a four-year delay. The project has faced legal challenges and protests over its plans to build the mega-telescope atop Mauna Kea, a mountain that is sacred to Native Hawaiians.

With a major court battle now behind the project, “the day for construction to begin has arrived”, said Hawaii governor David Ige on 10 July.

Astronomers have designed the TMT as part of the next generation of ground-based observatories, joining two other enormous telescopes that are under construction in Chile. TMT officials previously estimated the project’s cost at US$1.4 billion, but that number has almost certainly risen given the delays.

The first attempt to begin constructing the TMT, in April 2015, was halted almost immediately by protesters who say that building the telescope on Mauna Kea would further desecrate the mountain, which is already home to 13 astronomical observatories. In December 2015, Hawaii’s supreme court revoked the TMT’s construction permit and sent the project to Hawaii’s Board of Land and Natural Resources, which oversaw a second permit process and more public hearings.

Unsure whether they could build in Hawaii, project leaders began considering an alternate site in the Canary Islands. But in October 2018, the state’s supreme court ruled that the telescope’s second construction permit was valid, opening the way for work to restart on Mauna Kea.

One set of TMT opponents filed a fresh legal challenge this week in a lower court in Hawaii, saying the state has not acquired a security bond as financial protection to cover the costs of restoring the site if the project is not completed.

Another group, the Hawaii Unity and Liberation Institute, issued a 10 July statement that said, “we will forever fight the TMT…we are prepared for intense and lengthy struggles but stand firm in kapu aloha — peace and nonviolence”.

The access road that leads up Mauna Kea— the site of many of the 2015 protests — will be closed starting on 15 July.