A satellite that can provide 24/7 surveillance of a third of the Earth’s surface relies on a rare mineral whose global supply is dominated by China, a new study has disclosed. The Ludi Tance-4 01 radar satellite, powered by gallium nitride (GaN) semiconductors, is the only satellite of its kind. It orbits 36,000km (22,000 miles) above the Earth and is able to stay in what is known as a geosynchronous orbit, which keeps it fixed over the same spot. This allows it to monitor both large areas of...