Most people shutter to think whether the 747 can hold and lift something the size of the Shuttle. Not so tough if you know the Shuttle weighs a paltry 172,000 lbs empty and a typical 747 can lift a payload of 247,000 lbs into the air. The SCA is no Trump jet in that, except for a few seats still in the first class deck, the rest of the aircraft has been stripped of wall panels and even insulation to keep the weight down. Way too noisy to hear the in-flight movie or your iPod.
Shuttle Carrier N905NA was used to ferry the retired Shuttles to their respective museums. It retired to the Dryden Flight Research Facility at Edwards Air Force Base in California after a short flight from Los Angeles International Airport on September 24, 2012. It now joins N911NA as a source of spare parts for NASA's SOFIA aircraft.
Here is one of the mounting points where they connect the Shuttle to the 747. Note the bit of NASA humor in the mounting instructions:
Here is the listing the number of ferry and free flights, in Silhouette, of the various Orbiters and the Phantom Ray on the port side of the SCA: