A mobile launcher platform (MLP), also known as mobile launch platform, is a structure used to support a large multistage space vehicle which is assembled (stacked) vertically in an integration facility (e.g. the Vehicle Assembly Building) and then transported by a crawler-transporter (CT) to a launch pad. This becomes the support structure for launch.
The use of mobile launcher platform is a part of the Integrate-Transfer-Launch (ITL) system, which involves vertical assembly, transport, and launch of rockets. The concept was first implemented in the 1960s for the United States Air Force's Titan III rocket, and it was later used by NASA for Saturn V, Space Shuttle, and Space Launch System.[1]
There are alternatives to ITL. Horizontal assembly and transport to the pad is used by Russia, by ULA for the Delta IV family, and by SpaceX for the Falcon 9 family. Vertical assembly on the launch pad is used for smaller launch vehicles and for the SpaceX Starship.