On this day in aviation history, NASA purchases a Boeing 747-100, the first of two Boeing 747 aircraft that would be the Shuttle Carrier Aircraft fleet. Initially, the Lockheed C-5 Galaxy was also considered, it "lost" the competition with the Boeing 747 because of the low wing configuration of the Boeing 747 and also because the US Air Force would not allow NASA to own the C-5, they would remain US Air Force property.
N905NA was the first aircraft and was purchased from American Airlines, A Boeing 747-123, after being modified by Boeing the aircraft was initially used for Wake Vortex testing by NASA Dryden and NASA for Shuttle tests. The modifications on the aircraft were extensive, not all of them were visible as a lot of modifications were performed inside the airframe, some of the modifications were:
Cabin interior and insulation was removed (except first class, which was retained for NASA staff)
Fuselage reinforced
Mounting points for the Space Shuttle were added
Additional vertical stabilisers were added to the horizontal stabiliser tips
Avionics upgraded
Engines upgraded
To facilitate crew egress during test flights an internal escape slide and explosives were installed to blow out a section of the fuselage. (this was removed after testing as the crew could possibly be ingested in an engine if they used this escape system)
Carrying the Space Shuttle gave a huge increase in drag, reducing the range of the aircraft to about 1000 nm (1900 km), while the standard B747-123 had a range of ~5500 nm (10.000km) with a maximum speed of Mach 0.6. If the aircraft was not carrying the Space Shuttle it had to fly with ballast to keep it within the Centre of Gravity limitations of the aircraft. It took 170 NASA staff to prepare a Space Shuttle carrying flight with the aircraft.
In 1988 NASA bought the second aircraft for the Shuttle Carrier Aircraft fleet, an ex-Japan Airlines Boeing 747SR-46 (A high capacity domestic variant for the Japanese B747 market). The aircraft registered N911NA underwent the same modifications as the first NASA Boeing 747.
NASA Shuttle Carrier Aircraft N905NA (foreground) and NASA 911 aircraft (rear)
Shuttle Carrier N911NA was retired on the 8th of February 2012, ferried to Dryden Flight Research Facility at Edwards Air Force Base in Palmdale, California and was used as a spare parts source for NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA) aircraft. It is now on display in Palmdale CA, USA.
Shuttle Carrier N905NA was used to ferry the retired Space Shuttles to the different museums. After completing that mission the aircraft was also flown to Dryden Flight Research Facility at Edwards Air Force Base in Palmdale, California to be used as spare parts like N911NA. However, it was determined that not enough parts were exchangeable. The aircraft is now on display at Space Center Houston with the mock-up Space Shuttle Independence mounted on its back.