Mobile launcher platform

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.

There are alternatives to ITL. Horizontal assembly and transport to the pad is used by Roscosmos, by the United Launch Alliance 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.

From 1967 to 2011, three platforms were used at the LC-39 to support NASA's launch vehicles at the Kennedy Space Center. Formerly called Mobile Launchers (ML), the mobile launcher platforms were constructed for transporting and launching the Saturn V rocket for the Apollo program lunar landing missions of the 1960s and 1970s. Each ML originally had a single exhaust vent for the Saturn V's engines. The Mobile Launchers also featured a 380-foot-tall (120 m) Launch Umbilical Tower (LUT) with nine swing arms that permitted servicing of the vehicle on the launch pad, and swung away from it at launch.

The Mobile Launchers were built by Ingalls Iron Works. The swing arms were constructed by Hayes International.

After the Apollo program, the bases of the Mobile Launchers were modified for the Space Shuttle. The Launch Umbilical Towers from ML-2 and ML-3 were removed. Portions of these tower structures were erected at the two launch pads, 39A and 39B. These permanent structures were known as the Fixed Service Structures (FSS). The LUT from ML-1 was taken apart and stored in the Kennedy Space Center's industrial area. Efforts to preserve the LUT in the 1990s failed due to a lack of funding, and it was scrapped.

In addition to removal of the umbilical towers, each Shuttle-era MLP was extensively reconfigured with the addition of two Tail Service Masts (TSM), one on either side of the main engine exhaust vent. These 9.4 m (31 ft) masts contained the feed lines through which liquid hydrogen (LH₂) and liquid oxygen (LOX) were loaded into the shuttle's external fuel tank, as well as electrical hookups and flares that were used to burn off any ambient hydrogen vapors at the launch site immediately prior to Main Engine start.

The main engines vented their exhaust through the original opening used for the Saturn rocket exhaust. Two additional exhaust ports were added to vent exhaust from the Space Shuttle Solid Rocket Boosters (SRBs) that flanked the external fuel tank.