The National Aeronautics and Space Administration (NASA) was established in 1958 and is responsible for America's civil space program, as well as research in aeronautics and space exploration.
From the Apollo program, which put humans on the moon for the first time, to more recent Mars Exploration missions, NASA has had many successful programs and missions. But there are also the ones we didn't hear much about, because they got abandoned somewhere along the way. The reasons range from budget constraints to technical problems and shifting priorities.
In this gallery, we look at NASA missions that had a lot of potential, but never went ahead. Click on to find out what they are.