Mobile Launcher Platform 1 or MLP-1, formerly Mobile Launcher 3 or ML-3 is one of three Mobile Launcher Platforms used at Kennedy Space Center Launch Complex 39. Saturn V and Space Shuttle launches were conducted from MLP-1 between 1969 and 2009. It was modified for use in the Constellation program but ended up being used only once for the Ares I-X launch before the cancellation of the program.
Mobile Launcher Platform 1 Wikipedia
MLP-1 was originally constructed as a Mobile Launcher for the Saturn V rocket, and was designated ML-3, or LUT-3. It was built by Ingalls Iron Works. Construction began in 1964, and was completed with the installation of the Launch Umbilical Tower hammerhead crane on 1 March 1965. The swing arms, which were constructed by Hayes International were added at a later date.
Following completion, ML-3 was used for five manned Apollo launches; Apollo 10, Apollo 13, Apollo 15, Apollo 16 and Apollo 17.
Following the launch of Apollo 17, ML-3 was the first of the Mobile Launchers to be converted for use by the Space Shuttle. The Launch Umbilical Tower was dismantled and placed into storage, and the base of the launch platform was modified to accommodate the locations of engines on the Shuttle. The platform was redesignated MLP-1.
In total, MLP-1 was used for fifty two Shuttle launches, between 1981 and 2009. It was used for the first Space Shuttle launch, STS-1, in April 1981. Following the launch of STS-119 in March 2009, it was transferred to Project Constellation. The platform was used only for the Ares I-X and was going to be disassembled after the launch. The Project Constellation was though cancelled and the ML was left unused.