ALT:captive-carry flights

Two two-man orbiter crews were chosen by NASA for the ALT flights: Civilian Fred W. Haise, Jr., and Lieutenant Colonel, USAF, Charles Gordon Fullerton, as well as Colonel, USAF, Joe H. Engle, and Commander, USN, Richard H. Truly. Haise was a veteran of Apollo. He had faced life-threatening perils as lunar module pilot of the Apollo 13 crew in 1970, when the explosion of an onboard tank, while en route to the Moon, disabled the spacecraft by knocking out its electrical power. Haise helped save his crew through his close knowledge of electrical systems. He also was an expert on the Lunar Module, which served as a lifeboat and enabled the crew to return safely to Earth. Haise was selected for the astronaut program in April 1966. He was backup lunar module pilot for Apollo 8 and 11, and backup commander for Apollo 16.

Selection of the other three men showed that the torch was being passed to a new generation, for none of them had flown Apollo. Nevertheless, all three were graduates of the Aerospace Research Pilots School at Edwards Air Force Base, with Truly staying on as an instructor. Outstanding aviators seek hazardous duty. Serving with Fighter Squadron 33 in the early 1960s, flying combat jets from the carriers USS Intrepid and Enterprise, he specialized in night carrier landings, which took away normal visual cues. He graduated quickly from test pilot to astronaut, for in November 1965 the Air Force chose him as one of eight men who were to fly the Manned Orbiting Laboratory. Following that programâ€™s demise Truly transferred to NASA in September 1969. He was a member of the support crews for all three manned Skylab missions and the U.S.-Soviet ASTP linkup in 1975.

Like Truly, Engle had no spaceflight experience as an Apollo crew member, though he was a member of the astronaut support crew for Apollo 10 and the backup lunar module pilot for the Apollo 14 mission. But this did not stop him from qualifying as an astronaut, for he made sixteen flights in the X-15. He repeatedly topped Mach 5; he also flew three missions that reached above fifty miles in altitude, thus meeting an Air Force criterion that gave him this qualification. This experience was invaluable, for the X-15 was the last winged space plane before the shuttle; its speed and altitude records would not be bettered until the shuttle flew to orbit. As a high-performance aircraft that made unpowered landings, the X-15 also helped Engle for the ALT series.

Fullertonâ€™s career also resembled Trulyâ€™s, for he had been a Manned Orbiting Laboratory astronaut, transferring to NASA as well when that program died. He was a member of the support crews for the Apollo 14 and 17 missions. Fullerton held bachelor and master degrees from California Institute of Technology in mechanical engineering. Significantly, he did not come up by flying hot jets or rocket planes. He served in the Air Force with bombers, flying the B-47 for the Strategic Air Command and then working as a bomber test pilot at Wright-Patterson AFB, a major developmental center. It was a long way from Wright-Patt to Edwards; when he qualified for MOL, this showed that his talents were exceptional indeed.

Crew members for the 747 carrier aircraft included pilots Fitzhugh L. â€œFitzâ€ Fulton, Jr., and Thomas C. McMurtry, who were joined by flight test engineers Victor W. Horton and Louis E. Guidry, Jr. Fulton, McMurtry and Horton were from the NASA Dryden Flight Research Center and Guidry was a flight engineer from Johnson Space Center.

Lieutenant Colonel Fitz Fulton retired from the USAF in 1966 after serving 23 years. He was a veteran multi-engine test pilot with wide experience as a launch pilot for the X-15 and manned lifting bodies, as well as on other experimental aircraft flight test programs. Fulton flew over 235 different types of aircraft and flew some 16,500 hours testing most of the USAF bombers and transports developed since 1950. He flew 55 combat missions during the Korean War in the Douglas B-26 Invader, was an XB-70 project pilot for NASA and the USAF and since 1970 was co-project pilot for the Blackbird program, flying the triple-sonic YF-12 research aircraft version.

McMurtry had been flying experimental aircraft for NASA since 1967. As project pilot on the Supercritical Wing, he made the first flight with the new airfoil shape. He flew as co-project pilot on the F-8 Digital Fly-by-Wire aircraft and the Supercritical Wing F-111, and as co-project pilot on NASAâ€™s 990 and C141 multi-engine aircraft. Horton was flight test engineer on the YF-12 at DRFC and had flown as launch panel operator of the B-52 air-launch aircraft. Guidry had flown as test engineer on the C-135 Zero-G studies and the C-130 Earth resources aircraft.

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The mated SCA Boeing 747 amounted to a new aircraft, a heavy one with an unusual shape that had never flown before. Thus, although the standard 747 had accumulated millions of flight hours in routine service with airlines, the mated N905NA had to start again at the beginning, with taxi tests. The plane with Enterprise on its back would not take off and head for the wild blue yonder, at least not yet. Instead, it was to trundle down Runway 04/22, the main concrete runway at Edwards, under power from its engines. These taxi runs would evaluate the technique of setting thrust for takeoff. They would also assess directional stability and control, elevator effectiveness during rotation prior to takeoff, airplane response in pitch, thrust reverser effectiveness, use of the 747â€™s brakes, and airframe buffet.

Three taxi tests took place with Dryden research pilot Fitzhugh â€œFitzâ€ Fulton at the controls, all in the single day of February 15, 1977. The first taxi test reached 76 knots, well below takeoff speed. Fulton then reversed thrust and slowed to 23 knots before applying the wheel brakes. Inspection showed no damage or overheating within the wheel assemblies, and Fulton received permission to turn his plane around and taxi in the opposite direction, at higher speed. This time he reached 122 knots. Fulton evaluated the elevator effectiveness during this run, raising the nose wheel momentarily between 95 and 100 knots. Again he reversed thrust and slowed, applying the brakes at 20 knots as his plane rumbled to a stop.

The third taxi test simulated an aborted takeoff, making good use of the 15,000 feet of runway length. Fulton accelerated to 137 knots, then cut the engines from takeoff power to idle. Pulling back on the controls, he applied elevator and raised the nose to a 5-degree pitch-up. The 747 rotated smoothly; Fulton held the nose wheel off the runway for some 1,500 feet before lowering it again. He then pushed the throttles forward and reversed thrust. This time he carried out a more demanding test of brakes, braking between 49 and 40 knots. He indeed had come close to taking off; the plane would have lifted from the runway at around 145 knots and a pitch angle of 6.5 to 7 degrees.

The tests took place amid the coolness of early morning, for in the California high desert in February, temperatures can be well below freezing. Hence the temperatures of the brakes and wheels never topped 140 degrees Fahrenheit, which was acceptable.

Fulton declared that his 747 responded so well that at times the flight crew could not tell that the orbiter was atop the fuselage, with a weight of 143,600 pounds. â€œAs is oftentimes the case,â€ he added, the actual carrier aircraft-orbiter combination handled better than what we experienced in the simulator.â€

Three days later, on February 18, Enterprise, with no one aboard, was taken aloft for the first time in a two-hour-5-minute-flight to see how the orbiter/747 combination handled. This was seat-of-the-pants flying. â€œOnce we weâ€™re airborne,â€ said Fulton before the flight, â€œthe thing that will be of interest to all of us is any buffeting from the orbiter on the tail of the 747. If some unusual shaking or vibration levels are encountered during any of the flights, weâ€™ll back off and fly at a previously cleared airspeed.â€

The 747 rotated smoothly to a seven-degree pitch and flew off the runway at 142 knots. Fitz Fulton kept the landing gear down until there was no chance of having to land immediately on the dry lakebed. He and his copilot, Tom McMurtry, soon found that stability and other handling characteristics were better than the simulator predictions. Followed closely by chase planes, they climbed to 16,000 feet and performed flutter and autopilot tests. Next came an airspeed calibration with a Cessna A-37, instrumented as a pace airplane, flying alongside.

Cruising at 250 knots, the flight crew evaluated stability and control, while load cells at the orbiterâ€™s supports measured its lift. They descended to 10,000 feet and slowed to 174 knots, for airspeed calibration at a variety of landing gear and flap positions. Fulton made a practice landing approach, finally touching down at 143 knots. He applied the brakes sparingly, allowing the plane to roll to the end of the runway.

This first inert orbiter captive flight obtained information on low-speed performance and handling qualities of the mated crafts and was accomplished almost exactly as planned. The 747 combined with Enterprise handled much closer to the standard 747 than was anticipated. The 747 crew stated they â€œcouldnâ€™t even tell the orbiter was aboard.â€

The second such flight took place four days later, February 22, 1977, expanding the envelope to 265 knots at the top altitude, 22,600 feet, and 285 knots at 16,000. At that peak, and again at 16,000 feet, Fulton conducted checks of flutter, airspeed calibration, and stability. The top speed exceeded the target airspeed for air launch, 270 knots. The crew also used a high-power setting, 46,900 pounds of thrust for each engine. They had not planned to do this, but found that they needed the extra power to achieve 265 knots at maximum altitude.

Flight two, the longest in the series, as they stayed in the air for more than three hours, accomplished a series of flutter and stability control tests. During the flight, the two right engines of the 747 were reduced to idle thrust. The rudder demanded greater deflection at reduce airspeed. But even at 120 knots, close to stalling speed, the rudder maintained its effectiveness, preventing sideslip.

Takeoff weight was 625,500 pounds, including the 143,600-pound Enterprise along with fuel for the hours of flight. But standard commercial 747-100 series could take off at a gross weight as high as 735,000 pounds, including up to 350,000 pounds of fuel. â€œWe are flying the airplane at much lower gross weights than a heavyweight 747 would be taking off from L.A. going to London,â€ said Fitz Fulton. â€œSo we arenâ€™t really taxing the airplane a lot.â€ Carrying the orbiter â€œjust puts the load in a little different place.â€

â€œOur overall impression, based on the two flights, is that the airplane is handling extremely well,â€ he added. â€œWeâ€™ve seen a slight increase in the aerodynamic noise and buffeting as the speed had increased, but both conditions still are within the acceptable range. The most important thing weâ€™re trying to do on these first flights is to satisfy ourselves that the combination is aerodynamically stable. We have flown two missions and now need two more to completely clear the flight envelope we want.â€

Flight three, on February 22, 1977, concluded the flutter tests and concentrated on stability/control/flight evaluation and airspeed calibration. Stability and control were evaluated by idling the outer right #4 engine on the 747 to simulate an engine failure. â€œThe carrier aircraft is very docile in the simulated engine-out tests,â€ Fitz Fulton said. â€œWe have more than enough rudder to control engine-out situations, which confirms the preflight predictions.â€

The flight crew made shallow dives from altitudes up to 26,000 feet, Maximum speed was 370 knots, well above that planned for separation. At 280 knots, the pilots noticed a considerable increase in buffeting. Fulton later said that â€œit seems like between 270 and 280 knots, the buffeting sort of takes a quantum jump in intensity.â€ This appears to have resulted from resonance, with the frequency of eddies in the disturbed airflow, aft of the orbiter, matching a natural frequency of the 747â€™s tail surfaces.

There was distortion as well; a chase pilot reported seeing skin ripples on the orbiterâ€™s tail cone, again caused by disturbances in the flow. Fortunately, the planned separation speed of 270 knots was below the region of increased buffet and was not expected to produce problems during air launch.

The program had called for six such captive-inertâ€ flights with Enterprise unpowered and unpiloted. But these first three had been so successful that Deke Slayton, the ALT manager, cancelled the last of them. The final two flights were to conduct the maneuvers of an air launch, though without such a launch, for Enterprise was to remain on the carrierâ€™s back.

Flight four took place on the last day of February. Fulton climbed directly to 25,000 feet and pushed over to initiate a series of shallow dives that simulated those of separation. This flight also simulated emergency descent of the mated vehicles and a missed landing approach. The emergency descent was accomplished by reducing the four 747 engines to idle thrust. The missed approach was performed by flying the mated vehicles within 20 feet off the ground, then returning the 747â€™s four engines to full thrust for a go-around.

Fitz Fulton ended the flight by demonstrating that the mated pair could land on short runways, such as the 7,500-foot strip at NASAâ€™s Marshal Space Flight Center. Fulton aimed his plane carefully and touched down within the first 1,000 feet of the long Edwards runway. Braking moderately, he brought the 747 to a stop at the 5,800-foot mark.

The final flight, on March 2, 1977, conducted complete simulations of two orbiter launch profiles. These called for the 747 to climb to maximum altitude and push over into a shallow dive to accelerate to the 270-knot separation speed. Using the high-power engine settings, Fulton started the first dive at 28,600 feet, the second at 30,100 feet. Descending at an angle of 5.7 degrees, the plane reached maximum speed of slightly above 280 knots.

At this speed, Fitz Fulton cut the throttles to idle and deployed spoilers to the maximum air-brake position. This placed the 747 in a high-drag configuration while the orbiter, angled upward on its mount by six degrees, was generating high lift. This produced rapid vertical separation, in effect, the orbiter dropped the 747. Load measurements at the orbiterâ€™s supports showed a separartion force approaching 0.8 g at conditions of release â€“ as much as anyone wanted. Any increase was likely to cause Enterprise to pitch up, lose forward speed, move rearward, and perhaps strike the 747â€™s vertical fin.

Fulton approached the runway and touched down in another short-field landing, duplicating that of flight four. â€œThe landings certainly indicate we could go to heavier braking and get into even shorter fields if necessary,â€ he told Aviation Week.

In all this, Enterprise had been inactive. She had carried no crew, serving merely as an inert aerodynamic mass. Soon it would be time for astronauts to sit in her flight deck. Soon this orbiter would fly on its own.

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Taxi test had taken only a day, in mid-February 1977, while the captive-inert tests, qualifying the 747, had covered no more than the following two weeks. But the ALT plan now called for nearly three months to elapse before astronauts would board Enterprise for the next round of flights. This allowed engineers at Johnson Space Center to refine their computer programs and mathematical models, using data from those tests. Those codes modeled the separation and descent of the orbiter. With them, astronauts training in simulators could achieve greater realism as they practiced and rehearsed.

NASA also used the time to work on the orbiter. It needed additional equipment, further certification of subsystem performance. In particular, the elevon actuators had to go back to the manufacturer for final qualification tests; then they had to this date slipped. Balky APUs were part of the reason; their proof testing took be reinstalled. The schedule called for resumption of flight on May 26, 1977, but longer than anticipated, for they had leaky seals. Meanwhile, astronauts Engle, Fullerton, Haise and Truly continued their practice sessions in the ground simulators and the Gulfstream aircraft.

HQ NASA News Release No. 77-116 stated on June 8, 1977:

â€œThe first manned test flight of the Space Shuttle orbiter has been rescheduled from June 9 to no earlier than June 16, 1977, at NASAâ€™s Dryden Flight Research Center, Edwards, California. The exact date is dependent upon successful completion of orbiter ground tests currently underway at Dryden. This flight begins the second phase of the Shuttle Approach and Landing Tests, a program designed to verify the aerodynamics and flight control characteristics of the orbiter while still attached to the 747 carrier aircraft.

The postponement is due to the malfunction of equipment associated with the shuttle orbiterâ€™s auxiliary power system. A leak developed in a fuel pump in one of the three Auxiliary Power Units causing a small amount of APU fuel (hydrazine) to vent overboard. This problem in the APU 2 developed during a mission run of the orbiter APU system, one of the final tests scheduled before the first manned flight. APU 2 will be replaced before another mission run is scheduled at Dryden. This work is expected to take between four and seven days.â€

Deke Slayton set a date of June 17, but that day brought three new problems: failure of an Inertial Measurement Unit, trouble with two of the four primary flight control computers, and a fault with the ejection seats. These were fixed the following day, June 18, 1977, allowing Haise and Fullerton to board the orbiter as it rested atop its carrier. Most of Enterpriseâ€™s onboard systems were operating, including two of three APUs and ammonia boilers in an active thermal control system.

But as the 747 was being towed into position to start its engines, its air-conditioning system sucked in toxic fumes from those boilersâ€™ vent tubes. Fitz Fulton, still the 747 commander, shut the cabin air vents as he and his crewmates donned oxygen masks. The ammonia dissipated, and the mated pair soon was on the runway, ready for takeoff.

Fullerton later said that the height above the ground of the orbiter cockpit gave a spectacular view. Neither he nor Haise could see any part of the 747, which made it feel as if they were flying alone. In fact, they would not do this until the next round of tests. The present, phase II series called for â€œcaptive-activeâ€ tests, with the orbiter piloted and powered up, while still remaining firmly attached to its carrier.

This first captive-active flight made no attempt to push the envelope. The 747/Enterprise combo lifted off from Edwards at just past 8:06 a.m. PDT. The flight was once around an oval that measured 78 miles on the straight sections and 10 miles through the curves. The mated vehicles were airborne for less than an hour, they flew below 15,000 feet, and did not exceed 180 knots. A DC-3 might have served as a chase plane. Indeed, the cruise speed was so slow that the 747 had to fly with flaps extended. But the crew was not out to break records; they wanted to see how Enterprise would perform in the air. Its working systems included APU, hydraulics, active thermal control, and electrical, the latter using this orbiterâ€™s fuel cells. All performed well.

The orbiter had a split rudder that served as a speed brake, with its two halves splitting open and angling to the sides of the vertical fin. The maximum deflection angle of each panel for 45 degrees, listed as 100 percent speed brake. Use of this brake proved to have a pronounced effect on the big 747, as Haise and Fullerton conducted tests at 60, 80 and 100 percent. Fitz Fulton found that at the last setting, drag was so high that he had to increase the 7474â€™s engines from cruise to climb power in order to maintain altitude.

In Houston, the Mission Control Center at Johnson Space Center took primary responsibility for flight operations. The earlier captive-inert flight had been controlled on the scene, at Dryden Flight Research Center, and this was the first time Houston had controlled a Space Shuttle in flight. This called for good real-time communications links, which encountered some interference from a transmitter at Miramar Naval Air Station near San Diego, more than 150 miles away. Still, Houston had communicated with astronauts as far away as the Moon. California was much closer.

The second captive-active flight took place ten days later, on June 28, 1977, with astronauts Joe Engle and Richard Truly at the controls of the orbiter, was designed to simulate the separation maneuver that would be used for the first free flight. Takeoff was at 8:52 a.m. PDT and during the initial climb-out various low-speed flight control system tests were performed by both the Enterprise and the SCA. A high-speed (310 mph) set of flight control system tests were then performed to assess the accuracy of predicted control surface responses and structural characteristics with respect to aerodynamic vibration.

The vehicles then climbed to 22,030 feet for a separation maneuver test. The 747 crew accomplished a pushover and descended at approximately 3,000 feet per minute. The orbiter elevons were positioned as they would be during an actual separation. Following the separation test, the vehicles climbed to 19,300 feet and established a six-degree glide slope to simulate an orbiter autoland mode fly-through. Engle and Truly monitored the Microwave Scanning Beam Landing System to ensure it was performing as expected â€“ it was. After waving off the autoland approach, the vehicles performed a normal landing at Runway 22.

Back on the ground, trouble appeared within an APU. It had a minor leak, but the leak increased as a result of the second flight, with the unit losing both oil and hydrazine fuel. The highly toxic fuel needed removal, which delayed the third flight until late July. Technicians used this time to install a pair of hundred-gallon tanks for hydraulic fluid, change out the #1 and #3 APUs, replace the #5 (spare) onboard computer, and put in new actuators for the main landing gear. This work was accomplished while the orbiter and SCA remained mated in the MDD.

The third and final captive-active flight was flown on July 26, 1977, with Haise and Fullerton in the orbiter for a 7:47 a.m. PDT takeoff. This was a complete dress rehearsal for the first free flight and consisted of once around an oval measuring 84 miles on the straights and 24 miles through the curves. During the climb-out various avionics checks and flight control surface deflections were conducted; again, Enterpriseâ€™s APU, hydraulic, power, and cooling systems were powered up.

Soon after takeoff a warning light went on, and Fullerton reported that the temperature on APU 1 â€œhad gone off scale to the overheat side.â€ He shut it down, not knowing that the problem was with a faulty sensor rather than the unit. The APU later proved to have worked properly. Enterprise continued her flight with two rather than three working APUs.

Using his enginesâ€™ maximum thrust, Fitz Fulton drove his 747 above 30,000 feet and pushed over, then cut his engine power and deployed spoilers. His speed increased to 272 knots as he approached the launch point at 25,620 feet, and he reported that he was â€œlaunch ready.â€ Fulton followed this with an approach to Runway 17, which had the microwave landing system, and aborted this approach to land as usual on Runway 22.

As a final touch after landing, while still mated to the SCA, Haise deployed the Enterpriseâ€™s landing gear as a final check prior to the first separation. This was the first time these wheels had been deployed during the ALT program. All captive flights revealed no reason not to proceed with the free flights, and the last two tail-cone-on captive-active flights were cancelled.