Astronauts must wear spacesuits to go on a spacewalk.
Tips
memory
宇航 (yǔháng) = space navigation, where 宇 = universe and 航 = navigate. Add 服 (clothing) and you have the suit for navigating space. Same root in 宇航员 (yǔhángyuán, astronaut).
culture
China's manned space program (神舟 Shenzhou, 天宫 Tiangong) put 宇航服 in the news - most recently the new-generation 飞天 (Fēitiān, 'Skyward') suits used on Tiangong space station spacewalks.
