The nine-month-long ALT program was conducted from February through November 1977 at the Dryden Flight Research Facility and demonstrated that the orbiter could fly in the atmosphere and land like an airplane, except without power-gliding flight.
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Two NASA astronaut crews-Fred Haise and Gordon Fullerton and Joe Engle and Dick Truly-took turns flying the 150,000-pound spacecraft to free-flight landings.
The ALT program involved ground tests and flight tests. The ground tests included taxi tests of the 747 shuttle carrier aircraft with the Enterprise mated atop the SCA to determine structural loads and responses and assess the mated capability in ground handling and control characteristics up to flight takeoff speed. The taxi tests also validated 747 steering and braking with the orbiter attached. A ground test of orbiter systems followed the unmanned captive tests. All orbiter systems were activated as they would be in atmospheric flight. This was the final preparation for the manned captive flight phase.
Five captive flights of the Enterprise mounted atop the SCA with the Enterprise unmanned and Enterprise's systems inert were conducted to assess the structural integrity and performance handling qualities of the mated craft.
Three manned captive flights that followed the five captive flights included an astronaut crew aboard the orbiter operating its flight control systems while the orbiter remained perched atop the SCA. These flights were designed to exercise and evaluate all systems in the flight environment in preparation for the orbiter release (free) flights. They included flutter tests of the mated craft at low and high speed, a separation trajectory test and a dress rehearsal for the first orbiter free flight.
In the five free flights the astronaut crew separated the spacecraft from the SCA and maneuvered to a landing at Edwards Air Force Base. In the first four such flights the landing was on a dry lake bed; in the fifth, the landing was on Edwards' main concrete runway under conditions simulating a return from space. The last two free flights were made without the tail cone, which is the spacecraft's configuration during an actual landing from Earth orbit. These flights verified the orbiter's pilot-guided approach and landing capability; demonstrated the orbiter's subsonic terminal area energy management autoland approach capability; and verified the orbiter's subsonic airworthiness, integrated system operation and selected subsystems in preparation for the first manned orbital flight. The flights demonstrated the orbiter's ability to approach and land safely with a minimum gross weight and using several center-of-gravity configurations.
For all of the captive flights and the first three free flights, the orbiter was outfitted with a tail cone covering its aft section to reduce aerodynamic drag and turbulence. The final two free flights were without the tail cone, and the three simulated space shuttle main engines and two orbital maneuvering system engines were exposed aerodynamically.
The final phase of the ALT program prepared the spacecraft for four ferry flights. Fluid systems were drained and purged, the tail cone was reinstalled, and elevon locks were installed. The forward attachment strut was replaced to lower the orbiter's cant from 6 to 3 degrees. This reduces drag to the mated vehicles during the ferry flights.
After the ferry flight tests, OV-101 was returned to the NASA hangar at the Dryden Flight Research Facility and modified for vertical ground vibration tests at the Marshall Space Flight Center, Huntsville, Ala.
On March 13, 1978, the Enterprise was ferried atop the SCA to NASA's Marshall Space Flight Center, where it was mated with the external tank and solid rocket boosters and subjected to a series of vertical ground vibration tests. These tested the mated configuration's critical structural dynamic response modes, which were assessed against analytical math models used to design the various element interfaces.
These were completed in March 1979. On April 10, 1979, the Enterprise was ferried to the Kennedy Space Center. mated with the external tank and solid rocket boosters and transported via the mobile launcher platform to Launch Complex 39-A. At Launch Complex 39-A, the Enterprise served as a practice and launch complex fit-check verification tool representing the flight vehicles.
It was ferried back to NASA's Dryden Flight Research Facility on Aug. 16, 1979, and then returned overland to Rockwell's Palmdale final assembly facility on Oct. 30, 1979. Certain components were refurbished for use on flight vehicles being assembled at Palmdale. The Enterprise was then returned overland to the Dryden Flight Research Facility on Sept. 6, 1981.
From May 16th to June 12, 1983, Enterprise was ferried on a 28 day European goodwill tour. During that time it remained bolted to the top of the Boeing 747 Shuttle Carrier Aircraft. United States highlights on the the tour included stops at Peterson Air Force Base, Colorado Springs; McConnel Air Force Base, Wichita Kansas and Wright-Patterson Air Force Base, Dayton, Ohio. It then flew to Goose Bay, Labrador/Newfoundland Canada and on to Keflavik Naval Air Station in Iceland where it stayed overnight. The 747 and Enterprise then flew to Fairford Royal Air Force Base in England; Bonn-Cologne, West Germany and then Paris France (Paris Air Show - May 24-June 5, 1983). On the return flight it flew thru Italy and then a stop in Ottawa Canada. It returned to Dryden Flight Research Facility on June 12th.
In the April-October 1984 time period, Enterprise was ferried to Vandenberg Air Force Base in California and to Mobile, Ala. From there it was taken by barge to New Orleans, La., for the United States 1984 World's Fair.
In November 1984 it was ferried to Vandenberg Air Force Base and used as a practice and fit-check verification tool. On May 24, 1985, Enterprise was ferried from Vandenberg Air Force Base to NASA's Dryden Flight Research Facility.
On Sept. 20, 1985, Enterprise was ferried from Dryden Flight Research Facility to the Kennedy Space Center in Florida. On Nov. 18, 1985, Enterprise was ferried from the Kennedy Space Center to Dulles Airport, Washington, D.C., and became the property of the Smithsonian Institution. The Enterprise was built as a test vehicle and is not equipped for space flight.
Following in the Enterprise's, the orbiter Columbia was created and it became the first Space Shuttle to fly into Earth orbit in 1981. Four sister ships joined the fleet over the next 10 years: Challenger, arriving in 1982 but destroyed four years later; Discovery, 1983; Atlantis, 1985; and Endeavour, built as a replacement for Challenger, 1991.
In the day-to-day world of Shuttle operations and processing, Space Shuttle orbiters go by a more prosaic designation. Enterprise is commonly refered to as OV-101, for Orbiter Vehicle-101.
Enterprise spent 8 years on display at the Smithsonian National Air and Space Museum's Steven F. Udvar-Hazy Center in northern Virginia. On April 27, 2012 it was transported by barge to the Intrepid Sea, Air & Space museum in New York City where it went on display on July 19, 2012.