Criticism of the Space Shuttle program costs through amortization. Development costs were expected to be recouped through frequent access to space. These claims were made in an effort to obtain budgetary funding from the United States Congress. Beginning in 1981, the space shuttle began to be used for space travel. However, by the mid-1980s the concept of flying that many shuttle missions proved unrealistic and scheduled launch expectations were reduced 50%. Following the "Challenger" accident in 1986, missions were halted pending safety review. This hiatus became lengthy and ultimately lasted almost three years as arguments over funding and the safety of the program continued. Eventually the
Space Shuttle retirement and then be replaced by a new vehicle. When the concept of the U.S. space station evolved into that of the International Space Station, which suffered from long delays and design changes before it could be completed, the service life of the Space Shuttle was extended several times until 2011 when it was finally retired. In 2010 the Shuttle was formally scheduled for retirement with "Atlantis" being taken out of service first after STS-132 in May of that year, but the program was once again extended when the two final planned missions were delayed until 2011. Later, one additional mission