The Luna Ring (or Lunar Ring) is a speculative engineering concept proposed by the Japanese construction firm Shimizu Corporation. It is a massive infrastructure project that envisions an 11,000 km belt of solar panels deployed around the Moon's equator. The concept originated around 2013 following the 2011 Tōhoku earthquake and tsunami and the subsequent Fukushima nuclear disaster, as Japan sought a reliable, clean energy source to replace its heavy reliance on nuclear power.
The mechanism of the Luna Ring is a form of Space-Based Solar Power (SBSP). The solar arrays would continuously capture sunlight, which would then be converted into microwaves and beamed to receiving stations, known as rectennas, on Earth. The Moon's rotation ensures that at least half of the ring is always illuminated, providing uninterrupted power. Construction is planned to be carried out by robots that would utilize In Situ Resource Utilization (ISRU), processing lunar soil (regolith) to create materials like concrete for the structure. The project is connected to the broader global discussion on energy security and could potentially supply energy for future lunar colonies. While the concept has not been formally replaced, its status remains a long-term proposal, with recent discussions highlighting significant challenges like the staggering logistical costs of transporting thousands of tonnes of hardware and the energy loss during atmospheric transmission. The idea is relevant to India's space ambitions, as it is discussed in the context of the new Indian Space Policy 2023 and the country's growing involvement in the lunar space race.