For many decades, starships in the likes of the Enterprise and Millenium Falcon were thought to be impossible to build due to the large amount of money that would be required to haul resources from sea level to outer space. Instead, slow sublight craft were used. It took the Venture Star six weeks to reach Mars in 1984.
In 1997, NASA announced the first line of exploration craft, the Explorer-class starship. But due to the disappearance of the LMS Explorer, the program for deep space exploration was scrapped. Instead, NASA decided to pursue colonization of local stars, such as Alpha Centuri.