IT sounds like an idea for a sequel to the hit science-fiction film “Interstellar”: an underwater city of 5,000 people that draws its energy from the seabed thousands of meters below.

    But if a Japanese construction firm gets its way, Ocean Spiral could be a reality within just a couple of decades.

    Shimizu Corp., which has a reputation for dreaming up grandiose schemes, said Ocean Spiral will “capitalize on the infinite possibilities of the deep sea” to accommodate human life, as rising sea levels threaten the survival of island communities.

    According to an artist’s rendering, the structure will be divided into three sections.

    A floating sphere with a diameter of 500 meters, just beneath the surface of the sea, will house business and residential zones and hotels. The pod will be connected to a 15-km-long spiral path that winds its way to the ocean floor 3 to 4 km below the surface. There, scientists will explore ways to excavate energy resources from the seabed.

    Officials at Shimizu said the project would take about five years to build, at an estimated cost of 3 trillion yen (US$25.39 billion). The firm believes the technology needed to build the structure and to sustain life below the surface of the ocean will be ready in as little as 15 years’ time.

    “This is a real goal, not a pipe dream,” Shimizu spokesman Hideo Imamura said. “The Astro Boy cartoon character had a mobile phone long before they were actually invented — in the same way, the technology and know-how we need for this project will become available.”

    The project is drawing on experts from Tokyo University, government ministries and energy firms to turn Shimizu’s blueprint into a reality.

    The firm hopes to secure funding from private industry and the government.

    “It would be great if research institutions and governments become interested in our project,” Masaki Takeuchi, the manager of the project, told the Asahi newspaper.

    Ultimately, Shimizu envisages an eco-friendly underwater city sustained by energy brought up from an “earth factory” on the ocean floor.

    The factory will use micro-organisms to turn carbon dioxide into methane, while power generators located along the ocean spiral will use differences in seawater temperatures to create additional energy — a process known as ocean thermal energy conversion.

    Desalinated water produced using hydraulic pressure will be pumped into the residential pod.

    The idea of creating communities in the sea resonates in Japan, where land-based communities are at risk from large earthquakes and tsunamis.

    Another of Shimizu’s ambitious projects is a lunar base.

    (SD-Agencies)