Footage of the Shenzhou-12 taikonauts training before the start of their mission has been released. Three Chinese astronauts are currently aboard the Tianhe core module of the country's space station. On Sunday, two of them ventured out for a spacewalk. To bear the severe test of the extravehicular environment, the taikonauts have received long-term underwater training on the ground. They remained underwater six hours each time in order to master the skill for their movements in a weightless environment.