Whenever the Space Shuttle was transported outside the confines of the Kennedy Space Center, it was first loaded on board a specially-modified 747 called the Shuttle Carrier Aircraft (SCA).
There were two 747s tasked for this operation, NASA 905 and NASA 911.
To accomplish the process a structure called the Mate/Demate Facility (MDF) was built. Three of these existed: one at Edwards AFB in California, one at the Kennedy Space Center in Florida, and one at the original home of the Space Shuttle in Palmdale, California.
The photographs on this page show the operation of the facility at Palmdale when the orbiter Columbia was returned there to undergo a major modification period that included the installation of the new glass cockpit.
This facility was unique out of the three, in that it was originally built to be transportable to any site around the world where a shuttle might be required to make an emergency landing. It was only utilized in this mode one time when Columbia was forced by weather conditions to land at White Sands, New Mexico at the end of mission STS-3 in 1982.
So as not to have to transport the orbiter over land from the facility at Edwards AFB when modifications had to be done in Palmdale, the portable structure was set up permanently in Palmdale, next door to the orbiter construction hangar. This way, the 747/Shuttle combination could land directly at Palmdale airport, taxi into the MDF, be unloaded, and put directly into the hangar.
The sequence here shows Columbia being lifted off the back of the SCA, the SCA being rolled backward out of the way, then Columbia being lowered gently to the ground where the wheels are extended so it can be rolled into the hangar.
With all future major modifications completed at the Kennedy Space Center in order to save money, this operation never happened again in Palmdale.
It is extremely unfortunate that soon after the modifications to modernize the original space-worthy orbiter, the Columbia was lost in a tragic re-entry accident over Texas on February 1, 2003 at the completion of STS-107. This was only the second mission after being returned to flight status.