During

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

Space Shuttle program The Space Shuttle program was the fourth human spaceflight program carried out by the U.S. National Aeronautics and Space Administration (NASA), which accomplished routine transportation for Earth-to-orbit crew and cargo from 1981 to 2011. I ...

, several missions were canceled. Many were canceled as a result of the ''Challenger'' and the ''Columbia'' disasters or due to delays in the development of the shuttle. Others were canceled because of changes in payload and mission requirements.

Canceled due to the late development of the Space Shuttle

In 1972, NASA's planners had projected for 570 Space Shuttle missions between 1980 and 1991. Later, this estimate was lowered to 487 launches between 1980 and 1992. The details of the first 23 projected missions, listed in the third edition of ''Manned Spaceflight'' ( Reginald Turnill, 1978) and the first edition of the ''STS Flight Assignment Baseline'', an internal NASA document published in October 1977, are presented below. Later in the development process, NASA suggested using the first manned Space Shuttle mission, STS-1, as a

sub-orbital A sub-orbital spaceflight is a spaceflight in which the spacecraft reaches outer space, but its trajectory intersects the atmosphere or surface of the gravitating body from which it was launched, so that it will not complete one orbital re ...

test of the Return to Launch Site (RTLS) flight profile devised for emergency abort scenarios. ''Columbia'' would have launched from Kennedy Space Center, then executed a 180-degree turn at a speed of , or 6.7 times the

speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as we ...

, in order to land at the Kennedy Space Center runway. The mission was canceled when astronauts refused to fly it, having deemed the plan to be too dangerous. STS-1 commander John W. Young recalled that "I said no. I said let's not practice Russian roulette, because you may have a loaded gun there. So we didn't."

Canceled between the first flight of the Space Shuttle (1981) and the ''Challenger'' disaster (1986)

Canceled due to the ''Challenger'' disaster

Canceled between 1988 and the ''Columbia'' disaster (2003)

Canceled due to the ''Columbia'' disaster

References

{{All U.S. Space Shuttle Missions Space Shuttle program

Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program n ...