Approach and Landing Tests

Enterprise separates from the SCA on its first solo flight as part of ALT, August 12, 1977
Operator	NASA
Spacecraft properties
Spacecraft	Space Shuttle Enterprise
Spacecraft type	Space Shuttle
Crew
Members	C. Gordon Fullerton Fred Haise Joe Engle Richard Truly
Left to right:Fullerton,Haise,Engle andTruly

TheApproach and Landing Tests were a series of sixteentaxi and flight trials of theprototypeSpace ShuttleEnterprise that took place between February and October 1977 to test the vehicle's flight characteristics. Of the sixteen taxi-tests and flights, eleven sawEnterprise remain mated to theShuttle Carrier Aircraft (SCA), while the final five had the shuttle separate from the SCA, with the on-board crew flying and landing the spacecraft.

The Space Shuttle program originated in the late 1960s as an attempt to reduce the cost of spaceflight by introducing areusable spacecraft. The final agreed design would feature a reusablespaceplane, a disposableexternal tank and reusablesolid-fuel rocket boosters. The contract to build the spaceplane, which eventually came to be known as the "orbiter", was awarded toNorth American Rockwell (laterRockwell International), with the first complete orbiter rolled out in 1976. Originally planned to be namedConstitution (due to its completion being in the year of theUnited States Bicentennial), a letter-writing campaign byStar Trek fans persuadedPresidentGerald Ford to change the name of the prototype toEnterprise.^[1] It was unveiled to the public on September 17, 1976, with several members of theStar Trek cast in attendance.^[1]

Upon the orbiter's entry into service,NASA began an extensive program of tests usingEnterprise to ensure all of the systems it had put in place for the Shuttle program functioned as designed.^[2] These tests would encompass not only the flight tests planned to test the flight characteristics of the orbiter, but also ground-based testing of thelaunch pad systems and procedures. In January 1977,Enterprise was taken by road from the Rockwell plant atPalmdale, California to theDryden Flight Research Center atEdwards Air Force Base to begin theflight test phase of the program, which had been christened by NASA as theApproach and Landing Tests (ALT).

The program lasted from February until October 1977, with a pair of two-man crews assigned to the orbiter:

Haise had previously flown as theLunar Module pilot ofApollo 13, and was named as the commander of the original STS-2 mission.^{[note 1]} Fullerton later flew as the pilot ofSTS-3 and commandedSTS-51-F.

This crew later flew onSTS-2. Engle was originally a USAF pilot on theX-15, and had already gainedAstronaut wings by the time he joined NASA. He flew his second Shuttle mission onSTS-51-I.^{[note 2]} Truly flew his second Shuttle mission as commander ofSTS-8.

In addition to the two assigned Shuttle crews, who would alternate crewing the orbiter, a flight crew was attached to theBoeing 747Shuttle Carrier Aircraft (SCA) for the entire program. This consisted of a captain and first officer, plus a pair of flight engineers:

Enterprise mated to the Shuttle Carrier Aircraft for one of the ALT captive flights (top) and a ferry flight (bottom). Note the higher nose position during the captive flight

The ALT program was divided into three distinct phases.^[4] The first phase was designated as the "taxi-test" phase, which involved the SCA and orbiter in a mated formation conducting taxi tests at Edwards Air Force Base to verify thetaxiing characteristics of the aircraft while carrying the orbiter. These tests did not involve the orbiter in any way beyond it being mated to the aircraft, so consequently it remained powered down and uncrewed. A total of three taxi-tests were performed on February 15, 1977. Following this, the program moved into its next phase.

The captive flight phase of ALT saw the SCA/orbiter combination in flight as a test of the SCA's flying characteristics while mated to the orbiter, and as an initial test of the orbiter systems in flight. This was subdivided into two phases:

There were a total of five captive-inert flights designed to test the flight and handling characteristics of the aircraft while it was mated to the orbiter. As with the taxi tests, this did not involve the orbiter beyond it being mated to the SCA, so it remained unpowered and uncrewed.

The captive-active flights were intended to determine the optimum profile required forEnterprise to separate from the SCA during the orbiter's free-flights. These were also intended to refine and test the orbiter crew procedures and to ensure the operational readiness of the orbiter's systems. For these three flights, althoughEnterprise remained mated to the SCA, it was powered and crewed.

The final phase of flight testing involved free-flights. These sawEnterprise mated to the SCA and carried to a launch altitude, before being released to glide to a landing on the runways at Edwards AFB. The intention of these flights was to test the flight characteristics of the orbiter itself, on a typical approach and landing profile from orbit.^[5][6][7]

For the approach and landing tests, a nose strut longer than those employed in later ferry flights increased the shuttle'sangle of attack relative to the 747. Prior to the orbiter being released, the 747 engines were set to full power and the paired aircraft entered a shallow dive. Increased air speed combined with the shuttle's higher angle of attack generated enough differential lift so that the shuttle was effectively supporting the 747.Load cells on the three attachment points monitored the forces, informing the crew when the attachments were in sufficient tension. The mechanical connection between the two aircraft was then severed by the use ofexplosive bolts and the shuttle essentially dropped the 747.^[8] The shuttle crew reported feeling an upward lurch on separation. The two aircraft then turned in opposite directions to maximize separation. The shuttle executed some more turns to evaluate its handling and glided to a landing.^[9]

There were a total of five free-flights between August and October; the first three sawEnterprise remain fitted with itsaerodynamic tail cone, intended to reduce drag when mounted on the SCA during flight. The final two had the tail cone removed, with the orbiter in its full operational configuration, with dummymain engines andOMS pods.^[10]Enterprise used an air data probe mounted on its nose for these flights. These five flights were to be the only timeEnterprise flew alone.^[11][12]

After flying missions onColumbia (STS-2) andDiscovery (STS-51-I), Engle reported that the flight and handling characteristics of the operational orbiters were similar to those ofEnterprise, except that he had to fly a steeper profile with the prototype, as it was much lighter than the operational spacecraft.^[13]

Following the free-flight tests,Enterprise was prepared for ferry flight tests, which were intended to ensure that the SCA/orbiter configuration was viable for flights of the duration between landing and launch sites.^[14]

Following the end of the flight test program,Enterprise was taken for testing with the external tank andSRBs infull-up launch configuration, to test both the structural responses of the "stack" itself and the launch procedures prior to the entry into service and first launch of the first operational orbiter. These tests first sawEnterprise taken to theDynamic Structural Test Facility, located at theMarshall Space Flight Center inHuntsville, Alabama, where the complete stack was subjected to vertical ground vibration tests, assessing the structural responses to a number of scenarios. Then, the orbiter was flown to theKennedy Space Center inFlorida, to test the procedures of assembling the stack in theVehicle Assembly Building, transporting it from the VAB to the launch pad, and to fit check the facilities and procedures atLC-39 to be used in launching the Shuttle.

• Space ShuttleEnterprise 747 takeoff
• Space ShuttleEnterprise 747 separation
• Space ShuttleEnterprise landing

• 1977 in aviation
• 1977 in the United States
• Space Shuttle missions
• Edwards Air Force Base
• Fred Haise

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