Shuttle Carrier Aircraft - Design and Development

Design and Development

The Lockheed C-5 Galaxy was considered for the shuttle-carrier role by NASA, but rejected in favor of the 747—in part due to the 747's low-wing design in comparison to the C-5's high-wing design, and also because the U.S. Air Force would have retained ownership of the C-5, while NASA could own the 747s outright.

The first aircraft, a Boeing 747-100 registered N905NA, was originally manufactured for American Airlines and still carried visible American side stripes while testing Enterprise in the 1970s. It was acquired in 1974 and initially used for trailing wake vortex research as part of a broader study by NASA Dryden, as well as Shuttle tests involving an F-104 flying in close formation and simulating a "release" from the 747. The aircraft appears in the background of a scene from The Six Million Dollar Man's second season episode "The Deadly Replay", which was filmed in 1974 at Edwards AFB.

The aircraft was extensively modified by Boeing in 1976. While first-class seats were kept for NASA passengers, its main cabin and insulation were stripped, mounting struts added, and the fuselage strengthened. Vertical stabilizers were added to the tail to aid stability when the Orbiter was being carried. The avionics and engines were also upgraded, and an escape tunnel system similar to that used on Boeing's first 747 test flights was added. The flight crew escape tunnel system was later removed following the completion of the Approach and Landing Tests (ALT) due to concerns over possible engine ingestion of an escaping crew member.

Flying with the additional drag and weight of the Orbiter imposed significant fuel and altitude penalties. The range was reduced to 1,000 nautical miles (1,850 km), compared to an unladen range of 5500 nautical miles (10,100 km), requiring an SCA to stop several times to refuel on a transcontinental flight. Without the Orbiter, the SCA needed to carry ballast to balance out its center of gravity. The SCA had an altitude ceiling of 15,000 feet and a maximum cruise speed of Mach 0.6 with the orbiter attached. A crew of 170 took a week to prepare the shuttle and SCA for flight.

Studies were conducted to equip the SCA with aerial refueling equipment, a modification already made to the U.S. Air Force E-4 (modified 747-200s) and 747 tanker transports for the IIAF. However, during formation flying with a tanker aircraft to test refueling approaches, minor cracks were spotted on the tailfin of N905NA. While these were not likely to have been caused by the test flights, it was felt that there was no sense taking unnecessary risks. Since there was no urgent need to provide an aerial refueling capacity, the tests were suspended.

By 1983, SCA N905NA no longer bore the distinct American Airlines red, white, and blue cheatline. NASA replaced it with its own livery, consisting of a white fuselage and a single blue cheatline. That year, this aircraft was also used to fly Enterprise on a tour in Europe, with refuelling stops in Goose Bay, Canada; Keflavik, Iceland; England; and West Germany. It then went to the Paris Air Show.

In 1988, in the wake of the Challenger accident, NASA procured a surplus 747-100SR from Japan Airlines. Registered N911NA it entered service with NASA in 1990 after undergoing modifications similar to N905NA. It was first used in 1991 to ferry the new shuttle Endeavour from the manufacturers in Palmdale, California to Kennedy Space Center.

Based at the Dryden Flight Research Center within Edwards Air Force Base in California the two aircraft were functionally identical, although N911NA has five upper-deck windows on each side, while N905NA has only two. The rear mounting points on both aircraft were labeled with humorous instructions to "Attach Orbiter Here" or "Place Orbiter Here", clarified by the precautionary note "Black Side Down".

Shuttle Carriers were capable of operating from alternate shuttle landing sites such as those in the United Kingdom, Spain, and France. Due to the reduced range of the Shuttle Carrier while mated to an orbiter, additional preparations such as removal of the payload from the orbiter may have been necessary to reduce its weight.

Boeing transported its Phantom Ray unmanned combat air vehicle (UCAV) demonstrator from St. Louis, Missouri, to Edwards on a Shuttle Carrier on December 11, 2010.

Shuttle Carrier N911NA retired on February 8, 2012 after its final mission to the Dryden Aircraft Operations Facility in Palmdale, California, and will be used as a source of parts for NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA).

Shuttle Carrier N905NA was used to ferry the retired Shuttles to their respective museums. It returned 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 will soon join N911NA as a source of spare parts for NASA's SOFIA aircraft.