HONOLULU (AP) — A group building one of the world's largest telescopes wants to start construction no later than April 2018— even if that means it will have to build the telescope somewhere other than Hawaii.

The Thirty Meter Telescope board decided last week to start identifying alternate sites in case the telescope can't be built on Hawaii's tallest mountain, where protesters invoking the sacredness of the land have blocked construction from progressing.

"We've made a major investment so far in getting ready for construction, and there are certainly some challenges still ahead within Hawaii so we feel we need an alternate site," Executive Director Ed Stone said. "We need to develop an alternate site so that we have that as an option if we need it."

The $1.4 billion telescope was supposed to start construction in April 2015. It's not yet known how much a three-year delay will add to the total cost of the project. The global project's partners have already invested $170 million through the end of last year for "designing and developing and getting ready — and we are ready — to begin construction on the mountain," Stone said.

The state Supreme Court in December ruled the state land board should not have issued a permit for the telescope before it held a hearing to evaluate a petition by a group challenging the project's approval. The ruling sent the matter back for a new contested case hearing.

The state Department of Land and Natural Resources is searching for a hearings officer in anticipation of the proceedings.

In order to begin construction by April 2018, telescope officials need to know by September 2017 that they will have access to Mauna Kea, Stone said.

Mauna Kea, selected over Chile's Cerro Armazones mountain in 2009, remains the preferred site, Stone said. Astronomers prefer Mauna Kea because its summit is well above the clouds, and it provides a clear view of the sky for 300 days a year. There's also very little air and light pollution.

It's too early to say which other high mountains could be alternate sites, Stone said. There will be a "full analysis of where there are sites that we can build TMT on, which will give us the science we're anxious to do," he said.

"Well, they should be looking at alternate sites," said Kealoha Pisciotta, one of the plaintiffs in the lawsuit challenging the permit.

She called the threat of the project leaving Hawaii "a measure to try to pressure somebody to make things happen faster than they should happen."

Stone denied that allegation: "It's not applying pressure. This is just what we need to do to build this telescope."

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Follow Jennifer Sinco Kelleher at http://www.twitter.com/JenHapa. Her work can be found at http://bigstory.ap.org/content/jennifer-sinco-kelleher.