|A Tale of Two Birds: Chief Pilot Compares the Mighty NASA 747s||
A NASA 747 Shuttle Carrier Aircraft departs with space shuttle Atlantis securely on top for its return to Kennedy Space Center, Fla. Atlantis landed at Edwards Air Force Base June 22 and after preparations at Dryden began its journey back to Florida. (NASA photo by Carla Thomas)|
Gordon Fullerton knows a thing or three about specially modified 747 aircraft.
That's what happens when you've been doing something for more than three decades.
Fullerton, who is the chief pilot for the NASA 747SP SOFIA - Stratospheric Observatory for Infrared Astronomy - has been piloting unusual 747 aircraft since 1983.
The NASA 747 SOFIA arrives at Dryden from Waco, Texas, where it underwent extensive modification at L-3 Communications Integrated Systems. Dryden chief SOFIA pilot Gordon Fullerton recently compared and contrasted the two types of 747 aircraft. (NASA photo by Lori Losey)
When the weather is not inviting at Kennedy Space Center, Fla., for a space shuttle's return to Earth, it lands at Edwards Air Force Base and requires transit back to Florida.
At Dryden, a device called the Mate/Demate Device is used to slowly lift the spacecraft onto the back of the 747 for its piggyback journey home. Fullerton is one of the NASA pilots that fly the mated shuttle/747 SCA "stack" back to Kennedy Space Center, where the orbiter is prepared for future missions.
Fullerton made the first of four checkout flights of the specially modified 747SP SOFIA on April 26. The fourth flight involved the aircraft's May 31 delivery to Dryden from L-3 Communications Integrated Systems in Waco, Texas, where it underwent major modifications that would enable it to carry a 17-meric-ton infrared telescope.
From a pilot's perspective, Fullerton said, the cockpit, aircraft layout and basic instrument setups of the two 747 models are very similar, but there are nuances in the different versions.
"There were differences that were intentional - there are two extra fuel tanks in the wings of the (Boeing SP model) because it was built for long-range flights like New York to Tokyo. The fuel panel has extra gauges to accommodate those," he explained.
Some differences are subtler.
"There are little quirky things in the cockpit that are different for no good reason, as far as I can see. I compiled a couple-page list of the little differences that I gave to Bill Brockett to watch out for - 'these things make it different,'" Fullerton said, referring to Dryden's other 747 pilot.
"Some of the more superficial things include the airspeed indicator on the SCA that has a digital Mach meter in the middle of it. For some reason, they took the same airspeed indicator in the SP and put a digital airspeed meter in the middle of it, and the Mach is separated to the side."
Both the SOFIA and the SCA aircraft are called 747s, but many of the similarities end there in terms of individual capabilities. Several enhancements were necessary to adapt the aircraft to their respective missions. Chief among these: the SOFIA 747SP carries a telescope system internally at 41,000-foot altitudes, while the NASA 747 SCA carries a 230,000-pound space shuttle on its back at 15,000-foot altitudes.
"The handling is definitely different," Fullerton said. "With the orbiter on top there is a steady rumbling vibration. ...The challenge there is flying at a low speed at the low altitudes you have to, and to dodge the weather across the country to avoid precipitation that would damage the tile protection system (heat shield) on the orbiter. It's less a handling problem than a performance problem and a navigation problem. The Shuttle Carrier Aircraft also burns lots of gas, twice as much as the SOFIA will."
For the SCA flight planner, that means scheduling in a few stops for refueling. And the differences don't end there.
"The SCA has tip fins on the horizontal stabilizer - they were added to increase directional stability when you have an orbiter up there, which 'blanks out' the normal vertical stabilizer. When there is no orbiter loaded, the SCA is, maybe, over-stable - so much so that it has a crosswinds limit lower than a normal 747," he said.
The SCA stack must fly at low altitudes because of the space shuttle's tolerance for cold.
"The shuttle can handle about minus-nine degrees Centigrade. Any cooler than that and there is a risk of freezing or damaging its sensitive systems," Fullerton said.
In addition, a support aircraft always flies ahead of the stack to search for the clearest weather paths, which allow pilots to avoid potentially damaging moisture.
That is in contrast to the SOFIA flights, which will "cruise high above the water vapor and fly at a minimum of about 41,000 feet," he said. "Missions will be as long as possible - the goal for SOFIA is to fly above 41,000 feet for about six and a half hours."
During those six and a half hours, science data will be collected. Due to their length and the specificity with which the aircraft must be positioned, the biggest challenges with these flights come in developing the flight plan and obtaining the necessary clearances to fly it.
While the SCA has a single destination, in Florida, the SOFIA will be based at destinations across the globe, such as New Zealand, for its science work. Missions in Earth's southern hemisphere are valued for the astronomical phenomena that can be viewed from that region.
There are tradeoffs with each aircraft, Fullerton said.
Due to the configuration of the stack and its precious - and heavy - cargo, the SCA has a lower threshold for crosswinds compared to that of a production Boeing 747.
SOFIA Program Manager Bob Meyer, far left, welcomes Dryden pilot Bill Brockett, center, and chief SOFIA pilot Gordon Fullerton to Dryden after the SOFIA aircraft arrived at the center from the L-3 Communications Integrated Systems facility in Waco, Texas. (NASA photo by Tom Tschida)
The issues that made mission managers reach for the antacids during early SCA flights and in the first SOFIA flights also differ.
Mission managers' concerns about the NASA 747 SCA centered on Enterprise safely separating from the host aircraft and then clearing the SCA's tail during the Approach and Landing Test program.
The 747SP is built for longer-range use than the classic Boeing 747. It has less yaw stability, or motion about the aircraft's vertical axis, because its fuselage is shorter. Concerns about the SOFIA 747SP hinge on modifications that have been made and their impact on the aircraft's structural integrity.
Test flights will determine whether the designs for the beefed-up SOFIA aircraft are correct and completed to specifications. One way a pilot tests the limits of an aircraft is to fly cautiously when engaging maneuvers that stress the aircraft's structure. Those stresses also will be measured with strain gages to validate the aircraft's ability to complete its full range of movements throughout the flight envelope.
"We don't want to hear any popping sounds," Fullerton added wryly.
For Fullerton, one thing is sure - when it's time for him to pilot either aircraft, he'll be ready for whatever it takes to get the big bird safely in the air and down again.