VOA慢速英语:三个国家向火星发射宇宙飞船

rover – n. a vehicle used for exploring the surface of a moon, planet, etc.

burden – n. someone or something that is very difficult to accept, do, or deal with

orbiter – n. a vehicle or device that travels around a planet or moon in space

cliff -- n. a high, steep surface of rock, earth, or ice