Shuttle Carrier Aircraft
Boeing team aids NASA, United Space Alliance for shuttle's return to Florida
Space Shuttle Discovery, riding atop a modified Boeing 747 Shuttle Carrier Aircraft, landed at Kennedy Space Center, Fla., at about 10 a.m. Eastern time Aug. 21. The shuttle left NASA's Dryden Flight Research Center at Edwards Air Force Base, Calif., Aug. 19 for its cross-country trek, which was roughly 2,500 miles and included several stops for refueling.
When Discovery returned from orbit on Aug. 9, a team of Boeing engineers and technicians from Palmdale, Calif., Houston, and Kennedy Space Center, Fla., were on hand to help examine the vehicle and prepare it for its return to Florida. Boeing's engineering design center experts assisted United Space Alliance (USA) technicians with the processing work to get Discovery ready for the trip.
The Boeing Palmdale Facility has provided a variety of logistical support for the USA efforts at Edwards Air Force Base. Additionally, "Palmdale has provided hardware and tile materials items to support the ferry flight preparations back to KSC," said Bob Kahl, Boeing director for operations at Palmdale. "The efforts of both the Logistics and Thermal Protection System operations have been outstanding." Kahl said about eight people on his team have been supporting the operations since the shuttle landed.
Engineers faced some unique challenges while preparing for this ferry flight, one of which was assessing the extra weight in the aft of the orbiter. Not only did rainwater seep into the vehicle while at Dryden, adding pounds, but the shuttle was also carrying a Multi-Purpose Logistics Module. This MPLM was full of about 7,000 pounds of items offloaded from the International Space Station. Boeing is NASA's prime contractor on the ISS. Boeing engineers assessed the impact of the added weight to determine the necessary steps to ensure the shuttle's center of gravity was balanced before it was placed on top of the 747.
Doug Cline, one of several Boeing Vehicle managers, explained that they go through all the in-flight anomalies to determine if any of those impact the ferry flight, polling each subsystem manager for their assessment much like a flight readiness review.
"This was a heavy vehicle from a ferry flight perspective," said Cline. "Our Mass Properties Sub-System manager had developed a plan ahead of time. Since the vehicle was heavy in the aft end, we added a couple of pallets with weights in them on the floor of the crew mid-deck and weighted lockers."
About 1,300 pounds of ballast were added into the crew module. "We needed more weight up front, so we also left in 1,650 pounds of equipment that would normally come back on a truck," said Cline.
The Shuttle Carrier Aircraft can carry a 240,000-pound orbiter, and Discovery weighed in -- with the additional ballast and equipment -- at about 228,000 pounds.
Any tile damage greater than an inch had a clear liquid sealant applied to keep the tile substrate from eroding during the ferry flight back. "NASA wants to preserve those cavities in the best condition possible for further analysis," said Randall Carter, a Thermal Protection System engineer sent from KSC to Dryden. "We also stitched down some damaged blankets and sealed it with a ceramic coating to prevent further damage."
Carter added that the team assessed the damage to the thermal blankets, tiles and Reinforced Carbon-Carbon panels and wrote up 57 problem reports on the vehicle's TPS. "We also removed eight protruding gap fillers (spacers located between the tiles) that had shaken loose when the vehicle landed," Carter said. The team is preserving the gap fillers for further analysis to determine why they de-bonded.
"It is not unusual to see protruding gap fillers after landing and the number varies from flight to flight," Carter said. "We saw no evidence of any unusual heating effects on the vehicle. The vehicle TPS looked good and we saw the typical small damage we have seen on past flights."
A damaged "close-out" blanket measuring 22 by 3.5 inches and located below the commander's window was also removed and sent to a Boeing lab at Huntington Beach for analysis.
Boeing provided additional engineers from orbiter structures and mechanical systems, propellants, electrical systems and handling to assess the SCA flightworthiness with Discovery on top.
"Our role is to handle any design issues with the fluid systems on the vehicle, such as the Orbiter Maneuvering System, Reaction Control System, fuel cell systems (which provide electrical power and water), hydraulics and oxygen systems," said Danny Fitzgerald, a Fuel Cell/Power Reactant Storage and Distribution (PRSD) sub-system manager at KSC. "650 pounds of cryogenic oxygen and 60-70 pounds of hydrogen were removed from the power reactant storage and distribution system to keep the tanks from being overpressurized as they heat up." In addition, most of the water is removed from the lines so it does not freeze during the flight back. "Those lines are not heated during the flight back because of limited power availability," Fitzgerald noted.
Boeing develops the top-level procedures, specifications and drawings on attaching the orbiter on top of the 747 using the Mate-Demate Device (MDD). "The biggest part of bringing Discovery back is lifting it up and putting it on top of the 747. USA folks do all the hands-on work, and we are out there in an advisory capacity helping them should they run into any difficulties with any repairs that need to be made," said Stephen Holmes, integrated team manager for Orbiter Structures and Mechanical Systems at KSC.
The orbiter is lifted up with the MDD, and the 747 rolls underneath and is attached to the 747 using a set of three attach mechanisms -- two aft and one in front, similar to the attach points used for the External Tank. Holmes added that his team also inspects the landing gear, external tank disconnect doors, payload bay doors, drag chute and the airframe.
Ferry flight unique hardware consists of a 10,000-pound aerodynamic tail cone installed over Discovery's main engine nozzles, carrier panels, External Tank ferry flight doors, cap and plug sets, Auxiliary Power Unit vent drain line covers and other items that are installed on the orbiter. "Installing the tail cone is a major operation that can sometimes be more art than science," Holmes said. The tailcone and vertical stabilizers on the tail reduce aerodynamic drag and smooth out the airflow over the orbiter during the ferry flight.
NASA Shuttle Carrier Aircraft ferry flights follow an Air Force C-5 cargo pathfinder plane and fly only during daylight hours while staying clear of any high winds and rain.