A girl in a military uniform poses for a photo after the see-off ceremony before the launch in Jiuquan, Gansu province, China, 25 April 2024. China's Shenzhou-18 manned spaceflight mission with three astronauts is the third manned spaceflight mission of China Space Station's development phase. The mission will last for about six months and the crew will carry out tasks such as installation, commissioning, maintenance, repair, and experiments in space. (Photo by Wu Hao/EPA/EFE)

The NASA Extreme Environment Mission Operations (NEEMO) 21 mission began on July 21 as an international crew of aquanauts splashed down to the undersea Aquarius Reef Base, located 62 feet below the surface of the Atlantic Ocean in the Florida Keys National Marine Sanctuary. The NEEMO 21 crew will perform research both inside and outside the habitat during a 16-day simulated space mission. During simulated spacewalks carried out underwater, they will evaluate tools and mission operation techniques that could be used in future space missions, including journeys to Mars. (Photo by Karl Shreeves/NASA)