Space exploration Timeline Worksheet
But the program has not been without its problems. Faced with pressures to develop a reusable space transportation system, NASA in the 1980s took on military and commercial payloads in order to survive. The need to accommodate different kinds of payloads resulted in conflicting design requirements that would jeopardize the shuttle's safety—the 1986 Challenger disaster struck a huge blow to the program. When shuttle flights resumed in 1988, the program returned to its original mission of science exploration. But the shuttle's safety issues were not over—NASA's decision to ignore engineers' concerns about foam shedding from external fuel tanks cost the agency its second shuttle and crew when Columbia disintegrated over Texas in 2003.
The report issued by the Columbia Accident Investigation Board set into motion NASA's next transformation—a vision put forth in 2004 by President George W. Bush to replace the shuttle with new spacecraft that can take astronauts to the moon, Mars, and beyond.
Known as Constellation, the program will be based on existing, proven technologies and will be designed to dramatically improve safety by launching crew and cargo separately and incorporating a crew escape system.