By Maxim Shemetov WENCHANG, China, Aug 20 (Reuters) – On a sweltering August night, thousands on China’s Hainan island thronged the beaches around the Wenchang Space Launch Site, phones raised, waiting for a show. Shortly after 8 p.m., the Long March 7A rocket blasted off. The crowd roared as its ascent lit up the night sky. Moments later, the uncrewed rocket turned into a ball of fire in midair, an unforeseen blast confirmed by Chinese state m…