Challenging the unknown has been a human instinct since we were born, and exploring outer space is extension of curiosity and aspiration to knowledge in modern times. The most essential difference between human beings and animals is the constant search for the unknown, whose ultimate goal is to answer the question “Where do I come from? Where am I going?” It is impossible to find the answer of such questions in the real world, therefore, people will transfer their attention to the vast outer space. It is these questions that have become the driving force for human exploration of the universe. In addition, space exploration has inspired the scientific spirit of all mankind.
