Even after making tremendous progress (or moving fast on the path of progress) in virtually all the areas of science, progress in Space science and its exciting world has remained comparatively slow. Initially, only a few people were interested in or thought about new ideas of exploring space. Few went ahead and wrote their ideas in the form of theories (Copernicus was one such genius), books of space science, and on the other hand, some discovered and developed new gadgets (such as the telescope) to aid those who were interested in space.
As conceptualization, evolution, and research is a part of every new thing, every new idea, space science also witnessed various phases, such as a phase of conceptualization of ideas, the next phase of which was the human endeavor to find out new and unknown objects (such as new stars, and planets) in space with the help of telescopes, radars, and many more equipment. It gained acceptance as a totally new and potential branch of science, and scientists and astronomers emerged from all over the world to discover the undiscovered, to find the answers to those questions which always puzzled the human mind.
Great astronomers, astrophysicists, and leaders of the science world, like Aristarchus (who was probably first to put forward his theory that the sun is the center of the universe), Claudius Ptolemy, Hipparchus, Omar Khayyam, Nicolaus Copernicus, Pythagoras, Johannes Kepler (discovered and researched on planetary laws which are known as 'Kepler's Planetary Laws'), Cassini, Sir Isaac Newton (who developed and put forward the theory of gravity), Joseph Fraunhofer, Annie Canon, Albert Einstein, Edwin Hubble, and Stephen Hawking, emerged with their views and new theories regarding the unknown world around us. During the past few centuries, the progress in the field of space science has been very slow but constant. It witnessed many new developments (right from the concepts of the universe to the inventions of various equipment which helped in proving those concepts to be true, discovery of new objects such as comets, new planets and stars, etc.), and new horizons were touched.
Significant steps towards the development, improving our knowledge of space, were taken in the 20th century. Right after the invention of aircraft (by the Wright Brothers in 1903), new hope of exploring space and reaching new planets took shape. People started giving more emphasis towards this science, and millions of dollars were poured into its research and study. Further, after some progress in technologies, space science was looked upon as a new possibility towards the development of medical science, development and safe research on atomic/radioactive elements, exploring space to find out the possible traces of life on other planets, etc.
After the Second World War, it became one of the most important fields (as it is considered that the country that will lead the space race will rule the future world), in which every country [specially Russia (the USSR) and America] wished to prove their technical excellence over their competitors. The Cold War between countries worked as a fuel for the ongoing activities. Almost all the mighty nations plunged into the race of exploring space.
Russia was a leader in exploring space, and had sent quite a few very successful missions (one of which is its first satellite, 'SPUTNIK', then the second satellite 'SPUTNIK II', with a dog) into space, and it was even planning to send a man on the moon. America, being one of the strongest competitors, started pouring billions of dollars into space research. It even went ahead and formed the 'National Aeronautics and Space Association' (NASA) on 1st October 1958. America launched their first satellite 'Explorer-I', and also announced a series of such missions. The competition between both countries played an important role in bringing new pace to space science and its development. Further, Russia successfully landed their first space vehicle (Lung 2) on the moon (unmanned), and proved its might (after which, they sent a series of satellites on moon missions), and even started taking steps towards the launch of the first man on the moon.
The answer to their series of satellites and first woman in space was given by America, by its plans of sending the first man on the moon. America started with the series of Apollo missions (Apollo 7, 8, 9, 10), which were specifically aimed towards America's moon missions. Further, America landed its first man on the moon on July 16, 1969, when Apollo 11 successfully touched the surface of the moon, with astronauts Neil A. Armstrong, Edwin E Aldrin, and Michael Collins. Even though the mission was meant to help America lead the space race, it worked as a giant step for the mankind, and opened a completely new chapter in the history of space science.