Mobile Launcher Platform

After the Apollo program, the bases of the Mobile Launcher platforms were modified for the Space Shuttle (Space Transportation System) and renamed Mobile Launcher Platforms (MLP). The umbilical towers from Mobile Launchers 2 and 3 were removed. Portions of these tower structures were erected at the two launch pads 39A and 39B. These permanent structures are now known as the Fixed Service Structures (FSS).

In addition to removal of the umbilical towers, each Shuttle-era MLP was extensively reconfigured with the addition of two Tail Service Masts, 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 Space Shuttle main engines (SSMEs) vented their exhaust through the original opening used for the Saturn rocket exhaust. Two additional exhaust ports were added to vent exhaust from the solid rocket boosters 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.