The developer of the Thirty Meter Telescope signed a 75-year agreement with officials in the Canary Islands Wednesday giving the international consortium the right to construct and operate the giant telescope on the island of La Palma if Mauna Kea doesn’t work out.

The hosting agreement between the TMT International Observatory and Instituto de Astrofisica de Canarias clears a “major milestone” in securing the alternative site near the summit of La Palma’s highest mountain, according to a news release.

“This is an important step for TMT,” TMT Executive Director Ed Stone said. “We want to ensure we have by April 2018 a site suitable to start construction should Mauna Kea not be feasible. We now have a signed agreement and are moving ahead with the appropriate government approvals so that everything will be in place if needed.”

In addition to the April 2018 construction target date, TMT officials say they need “reasonably assured access” to Hawaii’s tallest mountain by the fall of this year.

But the $1.4 billion project, originally set to start construction on Mauna Kea two years ago, remains in limbo as the contested case hearing replay ordered by the Hawaii Supreme Court has yet to wrap up.

The testimony phase of the hearing is over, but the parties are still working to finalize the record before the hearing officer makes a final recommendation to the state Board of Land and Natural Resources.

Whether the board ultimately awards a construction permit, an appeal to the state’s highest court is highly likely.

Further complicating matters is the fact that another contested case hearing was ordered by a circuit judge to address a due-process issue in regard to the TMT’s sublease with the University of Hawaii. The state is appealing the ruling.

Even after all the regulatory approvals are secured, the issue of access remains thorny due to the protests likely to occur on the mountain. In 2015 a group of mostly Native Hawaiian protesters blocked construction vehicles headed to the summit three times.

Observatorio del Roque de los Muchachos is home to 12 telescopes, including the 10.2-meter Gran Telescopio de Canarias, and was recently tabbed as the site of the Cherenkov Telescope Array, which is set to become the largest ground-based gamma-ray detection observatory in the world.

Wednesday’s agreement lays out the terms for hosting TMT at the 7,861-foot observatory site, including its operation and eventual demolition, removal and site restoration.

The pact discusses the use of the land, access to infrastructure and common services. It also calls for headquarters facilities in La Palma and Tenerife, the most populous island of the seven Canary Islands, an autonomous community of Spain.

In return, Spain will receive 10 percent of the telescope’s observation time. By comparison, the agreement for Mauna Kea reserves 7.5 percent of observation time for UH astronomers.

Wednesday’s press release describes the La Palma observatory as offering “exceptional conditions” for TMT’s astronomy and certainly capable of meeting its core science goals.

But Thayne Currie, a Mauna Kea astronomer and member of the group Yes2TMT, said he’s examined various site data for La Palma, and he’s skeptical of TMT’s glowing praise.

“From a purely scientific standpoint, this is bit of like putting lipstick on a pig,” Currie said. “I question whether TMT would truly be able to meet its core science goals at La Palma: Mauna Kea is far, far better suited.”

In the news release, Instituto de Astrofisica de Canarias (IAC) Director Rafael Rebolo said, “We are excited about the possibility of welcoming TMT to the Observatorio del Roque de los Muchachos on La Palma. The capacity for outstanding astronomical discoveries is beyond thrilling. This hosting agreement serves well (TMT), Spain and the worldwide astronomy community.”

California Institute of Technology professor and TMT board member Tom Soifer added: “The true spirit of collaboration between (TMT) and Spain has been really uplifting. We thank the IAC and Spain for their tremendous support and for the warm welcome to (the La Palma observatory).”