ALT:free flights

During the week of August 8, 1977, a two-day Shuttle Readiness Review was completed â€“ all conditions were go. Enterprise was ready for free flight. Shortly after 8:00 a.m. on Friday, August 12, 1977, Fitzhugh Fulton and Thomas McMurtry guided N905NA down Runway 22, with astronauts Fred Haise and Gordon Fullerton at the controls of Enterprise. Haise had rehearsed the free flight the previous day in a Grumman Shuttle Training Aircraft; actual separation, which could not be rehearsed in advance, was the only way to prove that the Enterprise would lift clearly over the tall vertical tail fin of the SCA.

The SCA strained its engines to carry the 73-ton orbiter as high as possible; initially the heat of the desert air slowed the climb. Fitz Fulton made a routine climb to 30,000 feet and at 8:48 a.m. PDT, while flying at 310 mph, he stabilized his 747 in a pitch-down attitude of seven degrees, calling â€œlaunch readyâ€ as he approached launch altitude at 24,100 feet.

Fred Haise immediately fired the explosive bolt that bound the two craft. This brought separation, marked by a sudden thump and a brief sharp upward lurch. â€œThanks for the lift,â€ Haise told the 747 crew as the craft separated. Quickly there was a master alarm. A warning light went on as one of the identical redundant computers on the orbiter blinked out, cutting off flight-control accelerometers, without affecting the flight.

Haise held two degrees of pitch for three seconds, and then banked twenty degrees to the right to clear the 747, which entered a diving turn to the left. Pilots of the T-38 chase planes following the flight assured the crews of the SCA and the Enterprise that they were clear of each other. It quickly became clear that Enterprise was handling well; both pilots reported themselves delighted with the orbiter, which handled in unpowered flight as easily as design engineers had predicted. It was â€œa lot like flying a Concorde,â€ according to Haise, and Fullerton described it as a â€œvery crisp, very stable airplane.â€

Fred Haise lowered his nose and stabilized at nine degrees of downward pitch. Next came a practice landing flare to check th orbiterâ€™s handling characteristics at low speed. Gliding at 250 knots, he pulled up, raised the nose to eleven degrees of pitch, and executed a series of shallow-banked turns as his speed fell off to 185 knots.

During this flare, Mission Control at JSC made a mistake. Controllers believed the orbiter had remained steady in altitude during the flare and computed its lift-to-drag ratio accordingly. Houston told Haise that this ratio was well below the expectation, which meant that Enterprise would have to land very soon. Actually, the orbiter had plenty of lift, for it had not held level in altitude; it had climbed several hundred feet.

â€œI climbed some since I pulled up faster,â€ Haise told Aviation Week. â€œI could not tell any difference in the vehicleâ€™s response as the speed bled off. Of course, we were not doing any super maneuvers. I was making only small inputs in pitch and was limiting the bank angles to ten degrees. All the time I was doing this, we were slowing down and the vehicleâ€™s response characteristics looked the same.â€

Next Enterprise maintained a nine-degree nose down attitude to pick up speed for the approach. Fullerton took the controls and made a ninety-degree turn; Haise made one as well, placing his craft on final approach. But because he had followed the advice of Houston, he expected to drop relatively rapidly while accelerating somewhat slowly. Having more lift-to-drag ratio than Houston expected, Enterprise did no such thing; she stayed high and built speed quickly.

Haise now realized that he was too high and too fast. He used the speed brake and continued to aim for the runway, but he knew he would overshoot. There was nothing he could do. His only choice was to execute the overshoot, staying in the air until his speed could fall off. Haise flared and touched down, 2,000 feet beyond his aim point. Fortunately, Enterprise was using Runway 17, seven miles long as marked on the lakebed, with the lakebed itself providing a further five miles of overrun.

After five minutes and 21 seconds of free flight, Enterprise landed with a very low sink rate of under one foot per second. The speed at touchdown was as planned: 185 knots, or 213 miles per hour â€“ compared to a typical 747 landing speed of 170mph. The orbiter rolled for over two miles, with 100 percent speed brake and minimal use of the wheel brakes.

â€œI was hot and long,â€ Haise admitted, â€œbut that was not a big problem. For the first flight we were conservative. We wanted to make sure we got it on the ground and werenâ€™t going to worry about the aim point.â€ He had used his high speed to hold his craft just a few feet above the runway, settling down softly. The orbiter then threw up a large dust cloud from which the vertical fin continued to protrude. Spectators applauded; Enterprise rolled to a stop and the 747 flew overhead, in what Science writer Curtis Peebles called â€œan eagle saluting the success of its fledgling.â€

The event was carried live on network TV. With temperatures on the ground nearing 100 degrees Fahrenheit, as many as 70,000 visitors were present in the Mojave Desert, including a thousand representatives of the news media. Curtis Peebles was among them, reporting for *Spaceflightâ€™s* January 1978 edition:

*â€œIt starts with a long drive through the Southern California night. The hills and towns speed past merging into the high plains of the Mojave Desert. Long trails of red tail-lights stretch across the desert to the parking lot.*

*In the darkness, lights glow. Tiny figures move about. Slowly dawn banishes the stars. The clouds glow purple and red and so day comes to Edwards Air Force Base. You wait: the cars keep coming in a steady stream. Check the cameras and take a few pictures; focus the binoculars and wait.*

*Slowly the 747 and the Space Shuttle Enterprise back out of the support tower and move down the taxi way. Two T-38 chase planes wheel overhead; they, too, wait. Slowly, the 747/Enterprise moves to the runway. Crowds gather at every vantage point. They cover the two railroad lines; symbols of another transport system, another time, another frontier. As it sits on the runway, you begin to understand, to believe â€“ it is going to happen.Â*

*The wait is over now; 8:00 a.m.; a cry of thunder echoes across the base. Slowly, deliberately, the 747/Enterprise moves. Picking up speed, the ties with Earth are broken. Trailed by five chase planes, it enters the sky. Binoculars follow their travels. For almost an hour, final checks are made. Suddenly, all is set. The 747/Enterprise comes around. The countdown begins: 10 minutes, 5 minutes, one minute. Numbers running backward to zero.*

*Thousands of eyes search for a tiny black speck in the Sunâ€™s glare. Mission Control wishes them a good flight. The 747/Enterprise begins a gentle descent. As the assembled thousands see a glimpse, Fred Haise pushes a square white button which detonates the explosive bolts which join the two planes and begins a new age.*

*The radio announces â€˜separationâ€™ and applause breaks out. The 747 appears behind it, a thin contrail. At its peak, almost lost against an immense sky, a white wedge. The contrail disperses and you search again; then a black dot materializes, taking form, becoming larger.*

*The Enterprise is flying free. You watch it remembering forever these brief moments. That familiar shape, the black nose, the high rudder, the shroud covering the rocket engines â€“ so like an airplane, yet so much more.â€Â*

Gordon Fullerton said after the first free flight: â€œAfter Fred hit the separation button, seven explosive bolts released us with a loud kabang, and, as predicted, we went straight upâ€¦ Before we cleared the tail of the 747 one of our four General Purpose Computers had failed. I saw a big X on one of the displays in front of me, so I was not getting any current information. The procedure for a GPC fail was to pull some circuit breakers and turn off some switches. I referred to a cue card and got very busyâ€¦ Then I realized, kind of a shock, â€˜Hey, wait a minute! We are flying greatâ€¦ I missed the whole first part of the flight.â€™â€

The failed computer had lost synchronization with its fellows, which had voted it out of the system of four primary and one backup GPC. What had produced this loss of synchronization? Avionics specialists spent two weeks operating the computer system under simulated conditions at separation â€“ and traced the problem to a printed circuit board in the faulty machineâ€™s input-output processor. That board had been soldered in a way that proved to be faulty and had transmitted commands erratically. This brought the synchronization problem. Once this single board had been isolated, the avionics group succeeded in duplicating the sequence of events that had brought on the problem. One other circuit board had been soldered using the same methods. It was marked for replacement prior to the next free flight.

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That second free flight, flown by astronauts Joe Engle and Richard Truly, was made on September 13. Engle and Truly were test pilots, possessors of the Right Stuff, ready to blast into the sky with rockets roaring. But they were well aware that much work in flight test calls for nothing more dramatic than to move the stick and rudder pedals in predetermined ways and observe the resulting vehicle motion. They did this during the second flight, moving the controls by computer as well as by hand.

They separated from the 747 and Engle entered a dive, reaching 300 knots. Enterprise was to execute a tight turn, a maneuver that would dissipate excess energy during return from orbit, to reach the runway accurately. The turn indeed was tight, for they banked at 55 degrees. â€œI went right to 1.8 g in the turn and held that all the way down to below the 200-knot minimum target speed,â€ Engle said. â€œThe airplane felt very solid all the way through.â€ He pitched up as he turned; the airspeed fell off to 188 knots. He then stabilized his craft at 195 knots and carried through a second series of manual control tests. Now Truly took over, conducting additional control tests using the computer.

â€œI was managing the energy so that I could give the aircraft back to Joe at right airspeed, right altitude and the right place in the sky,â€ said Truly. â€œWe had planned the mission so that I would fly the orbiter down to 2,000 feet, which we felt would be a good place to give Joe plenty of time to get the landing set up. Approaching Runway 15, Engle aimed at a patch of green grass near the edge of the lakebed, a landmark that was easy to spot. After five minutes 28 seconds of free flight, Enterprise again touched down on the dry lakebed. She settled smoothly onto the runway at a measured distance of 680 feet from that target point. Again the orbiter made god use of the length of its landing strip, for it took over a minute to come to a stop, in a rollout that once more exceeded 10,000 feet.

The astronauts reported that the use of ailerons after nosewheel touchdown was not as effective in steering the orbiter as predicted, but other than that, the vehicle had performed well in flight. The most serious problem to come along during the flight was not in either of the flight vehicles:Â  the radar at Dryden failed 28 minutes into the captive portion of the flight, and almost caused an abort before it was brought back online.

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Ten days later, on September 23, the third free flight, piloted by Haise and Fullerton, took place on September 23, lasting five minutes 34 seconds. Testing the microwave landing system on Runway 17 originally had been one objective of the second free flight. But a few days after the first flight a tropical storm had swept across the high desert, dumping several inches of unseasonable rain on Edwards. Runoff water had pooled on that runway, flooding some two miles of its length. Since it would take up to three weeks to dry, program officials had decided to switch to Runway 15.

This time Runway 17 was dry, which meant that the third free flight could use the microwave landing system, which was a key element of the shuttle program, for it was to guide orbiters to a runway during their returns from space.Â  After separation from the 747, Haise and Fullerton executed another tight turn, followed by more tests of response to the aerodynamic controls. â€œWhen we completed that,â€ said Fullerton, â€œwe were very close to the planned eleven-degree glide slope as defined by the microwave landing system, so I pushed over and centered the guidance steering needles.â€

The system placed Enterprise under automatic control, with this orbiter rolling suddenly to acquire the exact runway heading. As it lurched, Fullerton inadvertently touched his control stick, causing the system to revert to manual operation. He then reengaged the microwave system, resuming automatic flight. â€œIt was absolutely smooth and was headed right for the advertised aim point on the lakebed,â€ he told Aviation Week. The automatic system flew the orbiter as it descended from 6,500 to 3,000 feet. Haise then took over, made a flare, and touched down at 187 knots.

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The first three free flights were deemed so successful that the final scheduled tail-cone-on flight was cancelled. The original plan of conducting a mated flight with the tail cone off was also scrubbed. During an early captive flight, with the cone on, Fitzhugh Fulton had remarked that his 747 â€œreminds me of the old B-36 days. The B-36 used to shake like this in turbulence, but this old bird shakes like this all the time.â€ Engineers hoped to reduce the effects of buffet by installing a yaw damper, a 1,000-pound weight mounted on springs in the 747â€™s nose. With this big plane rocking in turbulence of the orbiterâ€™s slipstream, this weight tended to oscillate strongly and to help keep the planeâ€™s motions more steady.

Fulton was to fly his 747 at progressively increasing speeds, from 180 knots up to 250, with the latter being faster than the speed for air launch. He also would make a simulated separation. If the buffeting from the mated vehicles became excessive, they could simply abort the flight and land on the lakebed. â€œWeâ€™ll have about twenty minutes for the ground team to look at the data and convince themselves that it is good,â€ Deke Slayton, head of the ALT program, said. â€œIf they arenâ€™t happy about it, weâ€™ll run another simulated launch and land. But if things are looking good, weâ€™ll go ahead and launch the orbiter.â€

So, for the fourth landing test, piloted by Engle and Truly on October 12, Columbus Day, the tail cone covering the three dummy main engines on Enterprise was removed. The orbiter now had the shape of a shuttle returning from orbit. Without the tail cone, glide time was reduced to just two minutes 34 seconds. Engle and Truly took turns with the controls, diving at more than twenty-five degrees while on final approach. A project report summarized what they learned: â€œThe tail-cone-off configuration showed no noticeable differences in handling qualities from the tail-cone-on configuration. Any increase in airframe vibration due to buffet at the aft fuselage was not noticed by the crew. The difference in tail-cone-off performance, however, was spectacular. Lift/drag modulation using both airspeed and speed brakes was much more apparent in the tail-cone-off configuration.â€

Engle and Truly flared and landed at 189 knots, which was expected, and with a sink rate of 3.5 feet per second, which was rather high. Previous free flights had used light braking and long runway rollouts, but this time they braked heavily, testing the orbiterâ€™s ability to stop more quickly. This cut some 4,000 feet from previous rollouts, as Enterprise came to a stop a mile after the nose wheel touched down.

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The final free flight, with Haise and Fullerton, happened on October 26, 1977, again without the tail cone, and witnessed on the ground by the British heir to the throne, Prince Charles, Enterprise made her last landing, her only one on a concrete runway. The flight plan was simple. As Slayton put it, â€œWeâ€™re going to do absolutely nothing except separate, come in and touch down at 5,000 feet down the runway.â€ They were to land on Edwards AFBâ€™s Runway 04, 15,000 feet in length. The aim point, one-third of the way on its length, left 10,000 feet for the landing and rollout.

The orbiter separated 51 minutes after takeoff at an altitude of 19,000 feet. During a total of two minutes and one second of free flight, the crew put the vehicle through a series of maneuvers, finding again that the gliding performance of the orbiter was better than predicted. This time however, as the crew set up their final approach, trouble started.

Coming out of the pre-flare, Enterprise was dropping at 334 mph, considerably quicker than planned. As they crossed the runway threshold, they were 20 knots too fast. In an attempt to slow the orbiter, Haise opened the speed brake early, but instead of slowing down, the speed increased, so Haise deployed the landing gear and pitched the nose down to make the runway impact point. Since Enterprise was unpowered, there was no option of making a second pass.

The orbiter rolled sharply to left and right as Haise struggled with his controls.Â  Then the rear wheels hit the tarmac hard. Instead of dropping her nose, Enterprise suddenly took off again, bouncing twenty feet into the air. Fullerton saw that they were in a Pilot Induced Oscillation (PIO), in which Haiseâ€™s own control movements were making things worse. He knew the orbiter could stabilize on its own and told Haise to loosen his grip on the stick. Haise described this as â€œthe normal thing you have to do to stop that sort of thing. So I let go of the stick and it stopped.â€

After a few anxious seconds, the orbiter smoothed out and stabilized for the remainder of the rollout, with the nose finally dropping onto the runway. Enterprise had touched down a few thousand feet past the planned mark, bounced, stayed in the air for another 2,000 feet, and then had come down for good. But although Haise and Fullerton had landed hot, with excessive speed, hard braking brought them to a stop with 3,000 feet of runway still in front of them.

A postflight review of flight data indicated that even earlier use of the speed brake would have reduced the airspeed problem. Also, Haise had lowered the elevons, which caused an increase of lift as the ballooning began after touchdown. Further research using other NASA aircraft, especially the F-8 Digital-Fly-By-Wire aircraft, led to correction of the PIO problem before the first orbital flight.