'In a Real Flight Environment': 40 Years Since Enterprise Took the Space Shuttle to Altitude (Part 1)

Four decades ago, this summer, a shuttle (though not a “space” shuttle) took to the skies above Edwards Air Force Base, Calif., to show the world what she could do. Outwardly, Orbiter Vehicle (OV)-101, nicknamed “Enterprise”, bore all the hallmarks of her five sisters who would someday voyage into low-Earth orbit, with the notable exception that she would never fly higher than about 25,000 feet (7,600 meters). The role of Enterprise and the men who flew her—Fred Haise, Joe Engle, Dick Truly and Gordon Fullerton—enabled a more comprehensive understanding of the shuttle’s flying characteristics in the low atmosphere and laid much of the groundwork for the maiden voyage of Columbia in April 1981.

Completed in March 1976, and rolled out of prime contractor Rockwell International’s Palmdale, Calif., facility, six months later, Enterprise was tasked with executing a series of captive-inert, captive-active and free flights in conjunction with a NASA-owned Boeing 747 Shuttle Carrier Aircraft (SCA). Original plans called for two orbiters, known as “Constitution” (Orbiter Vehicle-101)—which would perform the atmospheric Approach and Landing Tests (ALTs), before being upgraded for space missions—and “Columbia” (Orbiter Vehicle-102).

However, a mass of more than 100,000 letters to then-President Gerard R. Ford from Star Trek fans led NASA to bow to public pressure and rename OV-101 as “Enterprise”. It is believed that the space agency did not approve of the new name, but preferred “Constitution”, as it honored the bicentenary of the United States’s declaration of independence from Great Britain in 1977. When Enterprise rolled out of Rockwell’s Air Force Plant 42 on 17 September 1976, she had already undergone several months of horizontal ground vibration tests to validate her structural integrity and capacity to handle the stresses of simulated “launch” and “landing” phases. Unlike Columbia, Enterprise was not fitted with the provisions for “real” Orbital Maneuvering System (OMS) pods in her aft fuselage; nor did she carry the same integrally-machined vertical stabilizer tail element.

In January 1977, she was towed 35 miles (58 km) overland from Palmdale to Edwards, in readiness for the ALT series of tests. Early the following month, inside the gigantic Mate-Demate Device (MDD) at Edwards, she was attached to the top of the Boeing 747 SCA. The jumbo had been acquired by NASA from American Airlines in June 1974, in part because it was the biggest available aircraft to handle its oversized passenger. In order to lift the weight of the shuttle, virtually all of its interior provisions—seats, galley, air-conditioning ducts, wiring and plumbing—required removal or modification. Wind-tunnel testing had led to the additional of endplate-style vertical stabilizers on the horizontal tail and the power output of the jumbo’s four engines was significantly enhanced. At the time, it was anticipated that the SCA would be employed for 265 ferry flights, carrying future shuttles between their landing and launch sites.

And like Enterprise itself, the 747 was provided with an emergency ejection capability for its four-man flight deck crew. On 2 December 1976, it completed its first 100-minute test flight out of Seattle, Wash., preparatory to the following spring and summer’s operations in conjunction with Enterprise at Edwards Air Force Base, Calif. In mid-February 1977, the pair undertook several taxi tests along the runway. Each test occurred in the early hours of the morning, thereby reducing heating loads on the jumbo’s tires and brakes. All told, the 399,000-pound (181,000 kg) 747 and the 150,000-pound (68,000 kg) Enterprise would tip the scales as one of the heaviest vehicles ever to achieve flight.

During those taxi tests, the speed of the 747-Enterprise combo along the Edwards runway was carefully increased from 88 mph (143 km/h) to 140 mph (225 km/h) and finally to 155 mph (250 km/h). Procedures to abort the takeoff, whilst traveling at high speed, were successfully simulated, and the jumbo was put through tests of full braking, thrust reversers and speed brakes.

This set the scene for Enterprise to take to the skies above California’s Mojave Desert for the first time. The 1977 testing season would kick off with a so-called “Captive-Inert” series of flights, in which the unmanned shuttle would be transported to altitude for the first time in its career. For two weeks from 18 February, the 747 crew—pilots Fitz Fulton and Tom McMurtry and flight engineers Vic Horton and Louis “Skip” Guidry—performed no fewer than five airborne missions to evaluate the combined structural integrity of the two vehicles. A sixth flight was planned, but the initial five were so successful that it was dropped.

From the perspective of Fulton and McMurtry, the presence of the heavyweight shuttle “above” them had little adverse effect on their ability to control the aircraft. This was at least partly due to the presence of a large aerodynamic tail-cone, fitted onto Enterprise’s aft fuselage, covering her trio of “dummy” Space Shuttle Main Engines (SSMEs). Interestingly, the shuttle’s delta-shaped wings generated more “lift” than anticipated and some journalists remarked that the combo represented the debut of the world’s largest biplane. The last pair of Captive-Inert flights saw the SCA pilots demonstrate that they could achieve a complete halt in less than 6,000 feet (1,800 meters).

Following the completion of this Captive-Inert trials in early March, efforts entered high gear for the “Captive-Active” series in June-July 1977, which would include pilots aboard Enterprise, for the first time in actual flight conditions. These would see the shuttle firmly affixed to the top of the Boeing, but would lay the foundations for up to eight “Free Flights” in August 1977, during which Enterprise would separate from the SCA and glide to an unpowered, “deadstick” landing at Edwards.

Aboard the shuttle for the first Captive-Active flight were Fred Haise, veteran of the ill-fated Apollo 13 lunar mission, and Gordon Fullerton. Haise had been working shuttle issues since April 1973, when he was assigned as technical assistant to Aaron Cohen, then-head of the Orbiter Project Office at NASA’s Johnson Space Center (JSC) in Houston, Texas. On 24 February 1976, Haise was named to lead the ALT program, joined by fellow astronauts Fullerton, Joe Engle and Dick Truly.

Their training commenced in late October 1976 and the four astronauts utilized NASA’s fleet of T-38A Talon jet trainers—modified with special speed brakes—as well as the Shuttle Training Aircraft (STA). The latter, built by Grumman Aerospace of Bethpage, N.Y., was a twin-engine Gulfstream II business jet, modified to closely mirror the shuttle’s flying characteristics from 35,000 feet (10,600 meters). Two of these jets were delivered to NASA in June and September 1976.

This flight profile was accomplished through the independent control of six degrees of freedom with the jet’s flight control surfaces, as well as auxiliary direct lift, side-force control surfaces and an in-flight reverse thrust. The full six-degree-of-freedom shuttle equations of motion were mechanized within the Gulfstream II’s airborne digital computer. “The STA responses to the simulation pilot commands are compared with those of the orbiter and the STA control surfaces are driven to eliminate response differences,” NASA noted in September 1976. “The STA is consequently forced to follow the orbiter model.” Additionally, the astronauts trained at JSC in the Orbiter Aeroflight Simulator and Shuttle Procedures Simulator. The latter came to be nicknamed the “Spare Parts Simulator”, because of a tendency to cannibalize it to keep the more critical simulators running.

Haise, Fullerton, Engle and Truly were deeply involved in the design and development of software and flight procedures for the ALT series. “If I’d never flown the Enterprise, doing the training was challenging and intriguing in its own right,” Fullerton later told a NASA oral historian. “People say “How do you train?”, thinking, “Well, you go to a school and somebody tells you how to do it”. It’s not like that at all. Somebody’s got to write the checklist, so you end up writing the checklist, working with each subsystems person and trying to come up with a pre-launch checklist for the Approach and Landing Tests. So you’re doing the work [and] the learning comes from doing jobs that needed to be done.

“We worried about doing this deadstick landing, so we had to train for that. I built a gadget to work on the T-38 that would allow you with any given weight to set the power with the speed brakes down to simulate what the data said the orbiter would fly it at, so that we could go fly the pattern we intended to fly in T-38s, making steep descents, flaring and touching down. The shuttle training airplane, a Gulfstream II, was built as an airborne trainer, and so the four of us assigned to ALT served as the shuttle pilots along with a Gulfstream pilot to do many dives at the ground to get the aircraft built and working right.”

And 40 years ago, this week, after hundreds of hours in T-38s, the STA and various shuttle training simulators, Haise, Fullerton, Engle and Truly readied themselves for what they expected to be as many as 11 test flights through the summer of 1977.

The second part of this article will appear tomorrow.

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