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rover – n. a vehicle for exploring the surface of the moon, a planet or other space object
orbiter – n. a space craft that is designed to orbit the moon or another planet, not land on it
on schedule – phrase on time; as expected or planned
hover – v. to float in the air without moving in any direction
obstacle – n. an object that you have to go around or over; something that blocks your path
pile – n. a collecting of things lying one on top of another
solar system – n. our sun and the planets that move around it
