A mobile launcher platform (MLP) is a structure used to support a large multistage space vehicle. The vehicle is assembled vertically in an integration facility, such as the Vehicle Assembly Building, and then transported to a launch pad by a vehicle, like the crawler-transporter. At the pad, the platform serves as the structural and service interface for launch operations. The use of a mobile launcher platform is associated with the Integrate-Transfer-Launch (ITL) approach, in which launch vehicles are assembled and transported to the pad vertically, and launched from the same structure. The concept was first implemented in the 1960s for the United States Air Force's Titan III rocket, and was later adopted by NASA for the Saturn V, Space Shuttle, and Space Launch System. Similar systems have also been used by other launch providers, including United Launch Alliance (ULA)'s Atlas V and Vulcan Centaur, the Indian Space Research Organisation (ISRO), and the Japan Aerospace Exploration Agency (JAXA). Alternative launch integration methods include the use of a transporter erector, in which a vehicle is assembled and transported horizontally before being raised to a vertical position at the launch pad. This approach is used by most Russian launch vehicles, including Soyuz, as well as by SpaceX for the Falcon 9 family and previously by ULA for the Delta IV family. Another method is vertical assembly directly on the launch pad, which has been used for some smaller launch vehicles, the Saturn I family, the SpaceX Starship, and was proposed for Space Shuttle launches from the West Coast.
Kennedy Space Center
From 1967 to 2011, three platforms were used at Launch Complex 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 Space Shuttle external 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. The Space Shuttle assembly was held to the MLP at eight holddown points using large studs, four on the aft skirt of each Solid Rocket Booster. Immediately before SRB ignition, frangible nuts attached to the top of these studs were detonated, releasing the Shuttle assembly from the platform. Each MLP weighed 8.23 million pounds (3,730 tonnes) unloaded and roughly 11 million pounds (5,000 tonnes) with an unfueled Shuttle aboard, measured 160 by 135 feet (49 by 41 m), and was 25 feet (7.6 m) high. They were carried by one of two crawler-transporters (CT), which measure 131 by 114 feet (40 by 35 m), and 20 feet (6.1 m) high. Each crawler weighs about 6 million pounds (2,700 tonnes) unloaded, has a maximum speed of about 1 mile per hour (1.6 km/h) loaded, and has a leveling system designed to keep the launch vehicle vertical while negotiating the 5 percent grade (slope) leading to the top of the launch pad. Two 2,750 horsepower (2.05 MW) Diesel engines drive generators which in turn provide power to the electric traction engines. The MLPs were designed as part of NASA's strategy for vertical assembly and transport of space vehicles. Vertical assembly allows the preparation of the spacecraft in a ready-for-launch position, and avoids the additional step of lifting or craning a horizontally-assembled vehicle onto the launchpad (as the engineers of the Soviet space program chose to do), while also occupying the launch pad for shorter amounts of time and allowing for more expansive integration facilities.
Mobile Launcher Platform-1
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