The SCA or Shuttle Carrier Aircraft has been used since the first shuttle fight tests to carry the space shuttle from its construction site or its landing site. Prior to the first flight of Columbia in 1981. The SCA was used for the Approach and Landing Tests when it was dropped from the 747 to achieve an unpowered fight and landing at Edwards Air Force Base in California.
Most of the shuttle mission are now landing at Kennedy Space Center (the first flights were all landing in California where the runway on the dry lake bed is much longer than at Kennedy and allows for more margin) however in case of bad weather in Florida the shuttle will land in California. The SCA is then used to ferry it to KSC. Also from time to time the shuttle can be brought to its construction site for upgrading or revision, here also the SCA is used for ferrying.
This is the Revell 1/144 model, the modification from the original model is in the 747 livery which is the current NASA livery and not the former American Airlines colors that was given with the original box.