N905NA
The first Boeing 747 that NASA purchased was a -100 variant previously registered as N9668. According to Planespotters.net, American Airlines initially took delivery of this aircraft in October 1970. It was one of 16 747-100s that the carrier operated between 1970 and 1985. However, American soon found it was struggling to fill these mammoth airliners. //

NASA eventually withdrew N905NA from use in 2013, a year after the final shuttle-carrying flights. The following year, it was dismantled and then transported to the Johnson Space Center in Houston, Texas for preservation. Since 2016, it has been on display in an area of the center called ‘Independence Plaza,’ with a replica Space Shuttle attached to it.

N911NA
NASA did not obtain its second Shuttle Carrier Aircraft, N911NA, until 1988, shortly after the Challenger disaster in 1986. Planespotters.net reports that this 747-100SR (‘Short Range’) came from Japan Airlines, where it had entered service on high-capacity domestic routes in 1973. Its original registration was JA8117. //

Despite being the newer of NASA’s two Shuttle Carrier Aircraft, N911NA was the first to be withdrawn from service. This occurred in February 2012, and, before preservation, NASA used the aircraft as a spare parts source for its ‘SOFIA‘ flying telescope 747SP. N911NA eventually entered preservation two years later and is now on display at the Joe Davies Heritage Air Park in Palmdale, California.