The Boeing 747 is among the world’s greatest aircraft and has been popular with passengers and airlines alike since it first entered service with Pan American World Airways on January 22, 1970. As well as passenger and cargo airline use, it has also seen many other specialized, private, and VIP uses. Two that initially come to mind include the 747-200B currently serving as the US Presidential aircraft and the 747-400 that flew the English heavy metal band Iron Maiden on their 2016 world tour. But, one of the more unusual assignments for the iconic “Queen of the Skies” was its use as a ‘piggyback' aircraft for the NASA Space Shuttle. In fact, two 747s underwent a number of modifications in order to make that possible.
NASA introduced the re-usable Space Shuttle in 1977. After landing, the shuttle vehicle needed to be returned to its base at the Kennedy Space Center in Florida. It was unable to do this under its own power, of course, so a transport aircraft was needed. After initially considering the Lockheed C-5 Galaxy for the role, NASA selected the 747-100 as the aircraft to modify for this role, with the main reason being its low rather than high-wing design. The first Shuttle Carrier Aircraft (SCA) was a second-hand 747-100 from American Airlines, which had started service with the airline in 1970 and was taken on by NASA's Johnson Space Center in 1974. After extensive modification, it started shuttle service in 1977. Amazingly, it kept part of its distinctive American Airlines look until 1983, when it was completely repainted in NASA livery.
A second aircraft was procured in 1988 and entered service two years later. Previously operated by Japan Airlines, it was a 747SR (short range). The 747 is normally associated with long-haul operations due to the pioneering jumbo's ability to transport hundreds of passengers across continents. However, the "short range"variants of the jet were ordered by a handful of airlines. The 747SR had lower fuel capacity, but could carry more people onboard than its counterparts. It could hold up to 498 passengers in early editions, and over 550 customers in later versions. Additionally, it was made with a modified body structure. This feature allowed the jet to accommodate the extra stress from more frequent takeoffs and landings. There weren't many customers for the 747SR. In fact, it was primarily Japanese carriers that took these planes on for their domestic routes. The first variant was the 747-100SR. Japan Airlines took seven of these between September 1973 and April 1975. The flag carrier of Japan also took on two 747-100B SUDs in 1986. This variant had a “stretched upper deck” to accommodate more travelers. One of them went on to join NASA as the second Shuttle Carrier Aircraft.
There were plenty of changes made to both Boeing aircraft to handle the space shuttle. Much of each interior was stripped out (including all seats, except a small portion of those First Class seats at the front). The fuselage was strengthened to take the weight placed on it, and mounting struts were added on top of the fuselage to hold the shuttle in place. Major changes were also made to the tail, with vertical stabilizers added to the main horizontal stabilizers. This was to counter the change in the center of gravity when the shuttle was mounted. When flying without the shuttle, ballast weight had to be added to maintain that center of gravity. Once modifications were made to the fuselage, the shuttle could be lifted onto the top of the fuselage and latched into place. This was no simple operation - with some reports claiming it took up to a week for the crew to prepare and attach the shuttle prior to a flight mission! There were three struts used for attachment. The single forward strut was atop the 747 upper deck. The two aft struts were midway along the fuselage and these were affixed to the shuttle's external fuel tank.
The Shuttle Carrier Aircraft and its attachment struts also served another purpose besides ferry flights from the sometimes used shuttle landing strip at Edwards Air Force Base in California to its home base at the Kennedy Space Center in Florida. The Space Shuttle prototype Enterprise went through an extensive series of tests in 1977. These tests, and modifications, only applied to the first 747 SCA, not the modified 747SR from Japan Airlines which was added later. These tests included flights attached to the SCA to establish safe operation. But, they also involved free test flights of the shuttle. For this, the shuttle was carried to altitude by the SCA, then released to allow a free flight glide and return to land. The SCA and its struts were specially modified for these tests. A longer forward strut was used, which increased the shuttle's angle of attack relative to the SCA. And explosive bolts were added, which would sever the connection and allow the shuttle to glide freely. To safely achieve release, the paired aircraft started a high-speed shallow dive. The increased lift from the shuttle led to the situation where it was supporting the SCA beneath it (with the forces closely monitored by sensors). At this point, the bolts were exploded, and the shuttle would effectively drop the 747 beneath it.
An obvious question that comes to mind is: How could the aircraft fly with such added weight atop its fuselage? It would totally change the aerodynamic and performance capabilities of the original design. Drag was a major issue, and there was little that could be done to change that. With the increased drag and the shuttle's weight, the aircraft was much more inefficient and burned more fuel. Its range was reduced to around 1,025 nautical miles. Aerial refueling capability, which was later added to the Air Force One VC25A, was initially considered, but ultimately rejected. Instead, the SCA had to make frequent stops on its longer cross-country flights.
NASA eventually withdrew the initial SCA (Registration #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. Despite being the newer of NASA's two Shuttle Carrier Aircraft, that 747 from Japan Airlines (Registration N911NA) was the first to be withdrawn from service. This occurred in February 2012, and, before its preservation, NASA used it as a spare parts source for its Flying Observatory 747SP (Special Performance). That 747 (Registration #N911NA) eventually underwent its own preservation efforts in 2014 and is now on display at the Joe Davies Heritage Air Park in Palmdale, California.
The first Shuttle Carrier Aircraft (formerly with American Airlines) did the bulk of the heavy lifting. It operated seventy of the eighty-seven shuttle ferry missions during the program's operational phase, including forty-six of the fifty-four post-mission ferry flights from Edwards Air Force Base to the Kennedy Space Center. Along with the shuttles themselves, these modified 747s were engineering marvels in their own right and are a testament to the ingenuity of both NASA and Boeing.
Until next time…safe travels.
Very interesting George - a pity the UK launch of a rocket carrying satellites did not fare so well. The aircraft part was AOK but the rocket failed in its second stage. Hope someone remembered to take out insurance!!!