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