Fusion—the process that powers stars—promises nearly limitless clean energy, without the radioactive waste and meltdown risk of fission. But building a reactor that can sustain fusion requires an extraordinary level of scientific and engineering precision.

The X-shaped facility under construction in Mianyang, Sichuan, appears to be a massive laser-based fusion facility; its four long arms, likely laser bays, could focus intense energy on a central chamber. Analysts who’ve examined satellite imagery and procurement records say it resembles the U.S. National Ignition Facility (NIF), but is significantly larger. Others have speculated that it could be a massive Z-pinch machine—a fusion-capable device that uses an extremely powerful electrical current to compress plasma into a narrow, dense column.