The 747 has seen countless of varied roles, ranging from transporting passengers to cargo, becoming an airborne laser platform, presidential flagship, fire bomber, flying astronomy observatory (SOFIA) and in this case, a Space Shuttle Carrier.
Between 1977 and 2012, two converted 747-100's were used to transport the Space Shuttles across the states. Even more spectacular, they were closely involved in the initial flight testing of the space Shuttles. To test the flight characteristics of the new shuttles, they had to be actually flown to simulate the final phase of a space mission.
As a result, there were a handful of flights where the Space Shuttle disconnected from the 747 and glided her way back to the ground. Absolutely spectacular and it once again underlines the versatile nature of the Boeing 747.