On August 31st, 2018, NASA's Mobile Launch Platform (MLP) that will support the Space Launch System (SLS) rocket and Orion Spacecraft arrived at Launch Complex 39B for fit checks and system testing.
Before departing toward the launchpad, NASA's Crawler Transporter had to go pickup the MLP by going underneath it and then having it attached to the top. The 380ft Tall MLP travelled toward the launchpad at a whopping 0.7mph (1.13kmh) down the crawlerway.
The Mobile Launch Platform is a key part in launching NASA's next rocket, the Space Launch System and Orion Spacecraft. It holds the Crew Access Arm, which will allow crew members to board the Orion Spacecraft on the launchpad just prior to liftoff. It also has all the primary fuel and electronics connection umbilicals that supply the rocket and spacecraft with fuel and electricity on the launchpad. The MLP will be used in the VAB for assembly of the rocket as well.
After the MLP is done with system checks and fitting at LC-39B, it will go into the VAB where it'll be stored and continue to be worked on to make sure everything ready for the upcoming Exploration Mission 1, which will send the Orion Spacecraft out and around the Moon, then return to Earth.