Forty years ago, this fall, the first member of NASA’s space shuttle fleet was structurally complete and well on the way toward her first mission. Yet unlike the five sisters—Columbia, Challenger, Discovery, Atlantis, and Endeavour—who would follow her into orbit, Enteprise never traveled higher than Earth’s low atmosphere. Instead, she supported a series of critical test flights from NASA’s Boeing 747 Shuttle Carrier Aircraft (SCA) to remove many key unknowns about how the reusable spacecraft might one day perform in the low atmosphere and support unpowered, “deadstick” runway landings.
As outlined in yesterday’s AmericaSpace history article, Enterprise was rolled out from North American Rockwell’s Plant 42 in Palmdale, Calif., on 17 September 1976, whereupon she was transported overland to Edwards Air Force Base. In the early spring of the following year, she was flown to altitude atop the SCA for a series of “captive-inert” and “captive-active” missions, which allowed pilots and engineers to wring out controllability and landing-speed issues, before NASA astronauts Fred Haise, Gordon Fullerton, Joe Engle, and Dick Truly conducted a series of audacious Approach and Landing Tests (ALTs) in the high summer of 1977.
Haise and Fullerton were meant to take Enterprise on her first captive-active flight on 17 June, but were postponed by 24 hours when one of the shuttle’s computers required replacement. At 8:06 a.m. PDT the next morning, the 400,000-pound (180,000-kg) SCA lumbered off the Edwards runway, with the 150,000-pound (68,000-kg) Enterprise on her back. It was a strange sensation, sitting aboard the shuttle at such a great height above the runway. “When we first rode on top,” Haise recalled in a NASA oral history interview, “you couldn’t see the 747, no matter how [much] you’d try to lean over and try to look out the side windows. Not even a wingtip! It was kind of like a magic carpet ride. You’re just moving along the ground and you take off; and something below you [was carrying you]; you knew it was there, but you couldn’t see what was taking you aloft. It was also deceptive sitting up that high. Things always looked like it was going slower than it was, for your taxiing and particularly the first takeoff.” For an instant, Haise was convinced that SCA pilot Fitz Fulton had rotated too early. “It didn’t look like we were going fast enough.”
The feeling of nervous excitement and anticipation was equally intense for the crew of the Boeing. “Fitz was a great leader,” co-pilot Tom McMurtry recalled years later, citing the quiet moment, seconds before taxiing for takeoff on 18 June, when Fulton turned and shook hands with him and flight engineers Vic Horton and Louis “Skip” Guidry. “I thought that was a nice gesture. I think he just wanted to do that as a friend.”
During this flight, Haise and Fullerton were able to briefly test Enterprise’s aerosurfaces, rudder, and speedbrake. Ten days later, their colleagues Engle and Truly set off for a second run, conducting low-speed tests of her control system and simulating the separation manoeuvre from the Boeing that they would follow on the free flights. To accomplish these tasks, Fulton climbed to 22,000 feet (6,700 meters), before pushing-over and descending at around 3,000 feet (900 meters) per minute, allowing the astronauts to position Enterprise’s elevons in their ready-to-separate orientation.
Haise and Fullerton completed the captive-active roster on 26 July to finalise avionics and control surface checks before the green light was given for the free flights to commence in August. The only minor problem was a faulty sensor in one of Enterprise’s Auxiliary Power Units (APUs), which triggered a Caution-and-Warning (C&W) alarm in the cockpit and obliged Fullerton to shut it down. After landing on concrete Runway 22 at Edwards, Haise was able to deploy the shuttle’s landing gear, whilst still atop the Boeing, in readiness for the free flights.
Naturally, those free flights required close co-ordination between Enterprise’s crew and that of the Boeing 747. “Our main concern,” explained Joe Engle in his NASA oral history interview, “was to develop a separation maneuver with Fitz Fulton to optimize the separation between the two vehicles, both vertically and laterally. Fitz would put the combination in a slight dive to get the right airspeed in level flight, with the tailcone off. He would ‘dive’ the airplane and when he got on speed, he would call. We would separate and at that time the orbiter was sitting with a 15-degree angle of incidence; in other words, 15 degrees angle of attack and was trying to fly off the 747 at that time.
“Fitz would dump lift on the 747, throttle back to idle, so that as we came off, we didn’t slide back and take his tail off; then the two of us would turn in different directions as well, so that as soon as we lost energy and started to come back down, we didn’t come back down on top of him. In looking at the videos, there was lots of room, lots of separation, but initially we weren’t sure, so we optimized everything we could. We didn’t compromise anything by doing that, but we did have plenty of room for separation, and it was a co-ordinated maneuver. We would pull off to the right; he’d dive off to the left, then we’d go wings level and go right into the data-gathering maneuvers, because we had very little time to get data. We had about a minute and a half to get data and then, well, the rest of the time was flare and land, to get the gear down and touch down.”
Finally, on 12 August 1977, Haise and Fullerton performed Enterprise’s first independent landing. That morning, no less than 65,000 people gathered at Edwards. At 8 a.m. PDT, Fulton ran the SCA’s engines up to full power and, with surprisingly quietness, the Boeing and its shuttle passenger roared down Runway 22 and into the breaking dawn of the desert sky. It was followed by five NASA T-38 chase jets.
However, air temperatures at altitude proved higher than expected and the intended release time of 8:30 a.m. was missed. Eventually, at 8:48, Fulton nosed the SCA into a seven-degree dive. “The Enterprise is set,” radioed Haise. “Thanks for the lift.” He then pushed the separation button on his instrument panel and seven explosive bolts popped the shuttle away from the Boeing. Immediately, Fulton implemented a descending left turn, as Haise placed Enterprise into a right-hand turn and pitched upward to increase the separation distance. Meanwhile, from the right-hand pilot’s seat on Enterprise’s flight deck, Fullerton set to work remove circuit breakers and resetting switches. The shock of the separation had dislodged a small ball of solder and a transistor on one of the shuttle’s computers, causing a Cathode Ray Tube (CRT) monitor to halt.
“All of your control of the airplane is through fly-by-wire and these computers,” Fullerton recalled. “I had a cue-card with a procedure if that happened, that we’d practiced in the simulator, and I had to turn around and pull some circuit breakers and throw a couple of switches to reduce your susceptibility to the next failure. I did that and, by the time I looked around, I realized, hey, this is flying pretty good, because I was really distracted from the fundamental evaluation of the airplane at first.”
After briefing holding at two degrees of pitch, Haise banked 20 degrees to the right, heading for Edwards’ dry lakebed Runway 17. He maintained a nine-degree, nose-down attitude, putting Enterprise through a pair of 90-degree turns, then aimed for the runway centerline and opened the speed brake. Despite an erroneous call from Mission Control that his lift-to-drag ratio was lower than predicted—prompting Haise to fly his final approach at higher speed, conserving energy and extending the glide—Enterprise achieved a smooth landing. Due to the erroneous call, he touched down about 2,800 feet (900 meters) “long,” but had brought the first space shuttle to a smooth, unpowered landing, with pilots in control. Touchdown came 5.5 minutes after leaving the top of the SCA.
Watching from the ground, NASA Administrator James Fletcher began to panic that the shuttle would crash. “Landing gear! Landing gear!” he shouted at one stage, as the vehicle drew closer to the runway. It left him somewhat embarrassed among the throng of congressmen and senators. “The flying procedure,” explained astronaut Joe Allen, “is you can’t put [the gear down] until the airplane’s going a certain speed, lest you rip [it] off. That speed is very close to the ground, so it’s unnerving to watch. No question.”
By the end of October 1977, Haise, Fullerton, Engle, and Truly would have wrapped up no fewer than five landings and closed out the ALT program in spectacular style. “It handled better, in a piloting sense, than we had seen in any simulation,” said Haise, “either our mission simulators or the Shuttle Training Aircraft. The term I use is: it was tighter. [It was] crisper in terms of control inputs and selecting a new attitude in any axis and being able to hold that attitude; it was just a better-handling vehicle than we’d seen in the simulation.” Initial hopes that Enterprise would be outfitted as a spaceworthy vehicle ultimately came to nothing, as it proved more cost-efficient to upgrade Structural Test Article (STA)-099. Enterprise was briefly considered for potential upgrade again after the loss of Challenger, but lived out her days firstly in the Smithsonian and, from 2012, in the Intrepid Sea, Air & Space Museum in New York.
This is part of a series of history articles, which will appear each weekend, barring any major news stories. Next week’s article will focus on the 20th anniversary of John Blaha’s mission aboard the Mir space station.