After the "Columbia" accident, NASA decided that two test flights would be required and that activities that were originally assigned to STS-114 would need to be divided into two missions because of the addition of post-"Columbia" safety tests. Before the accident, "Columbia" had been assigned to missions STS-118 and STS-121. The STS-118 mission, also an International Space Station flight, was at first reassigned to "Discovery", but was later assigned to .