Approach and Landing Tests

Under the name of Approach and Landing Tests (English for approach and landing tests ), short- ALT, a series of experiments is summarized, with the U.S. space agency NASA in 1977 tested the flight characteristics of the newly developed space shuttle. Test object was the non-space -flying space shuttle prototype Enterprise ( OV- 101). The experiments presented in the run-up to the first space mission of the Space Shuttle to prove that the space shuttle could be controlled and landed in the atmosphere. In addition, they showed that it was possible they use the shuttle Carrier Aircraft, a modified Boeing 747 to transport. Basis for the test flights was the Dryden Flight Research Center at Edwards Air Force Base, California.

• 4.4.1 maiden flight

Background

In the 1960s, NASA developed a concept for a reusable space shuttle. Unlike the previously launched missiles it should be for a space flight capable, without prejudice to return to Earth. Since they would be used for further enforcement action, the cost of space flight should be significantly reduced. From the program, the Space Shuttle emerged. It consists of the so-called Orbiter - the actual space shuttle - an external fuel tank and two side of the tank mounted solid rocket. The latter return to the start of parachutes, the external fuel tank burns up in the atmosphere. The orbiter occurs at the end of a space mission back into the atmosphere and can be landed like an airplane. In order to test, among other things this last phase advance, the prototype Enterprise was built. Components that were not necessary for the ALT experiments were initially saved for reasons of cost during construction and should be retrofitted later. This mainly includes the expensive main engines and the heat shield, so the prototype for use in space was unfit. On 31 January 1977 he was transferred from its construction site in Palmdale, California, about 60 kilometers overland to the Dryden Flight Research Center at Edwards Air Force Base. There he was to prove the theoretically calculated skills in the real world as part of the Approach and Landing Tests.

Objective

The series of experiments focused on the last few minutes of a Space Shuttle mission after the shuttle re-entered the Earth's atmosphere and lapsed into deeper layers of the atmosphere and its speed has been reduced to in the subsonic range. Subject matter of the investigations were in particular the capabilities of the space shuttle, then to drive a runway and land safely there. The specified main objectives of the ALT program, were

• To demonstrate the airworthiness of the orbiter at subsonic speed,
• The operation of certain systems for the first orbital flight investigate
• The ability of the shuttle to check to manually and automatically controlled landing approaches and landings,
• Also check that the ferry was to at maximum load with different centers of mass in the situation.

In order to provide the evidence requested as possible under conditions as they were to be expected at the end of a space mission, was scheduled to leave the Enterprise fly and land in the atmosphere. For this purpose, they should be transported by a large aircraft in the air, dissolve in flight and self- control a runway. When a jumbo jet transport aircraft to the so-called Shuttle Carrier Aircraft (SCA ) was rebuilt. This would later be used to transport landed shuttles from landing site back to the Kennedy Space Center.

Crews

For the Approach and Landing Tests two crews of astronauts have been compiled for the Space Shuttle. The first consisted of the commander Fred W. Haise, Jr. and the pilot Charles Gordon Fullerton. Commander of the second crew was Joe Henry Engle; the second pilot was Richard Harrison Truly.

The crew of the SCA was made up of the pilot Fitzhugh L. Fulton, Jr. and Thomas C. McMurtry and flight engineers from the Louis Guidry, Jr. and Victor W. Horton.

Expiration

Overview

This complex task was not attempted in one step; rather, the ALT program was divided into several phases: First, roll tests showed the aerodynamic properties of the compound from transport aircraft and space shuttle on the ground. After that, the team made ​​several test flights; this remained the Enterprise initially turned off and unmanned, later it was activated and had a crew on board. Recently, the connection between Shuttle and aircraft was in flight isolated, the Space Shuttle flew and landed separately from the aircraft.

Rolling tests (taxi tests)

In preparation for the later test flights took place on February 15, 1977 three rolling tests, so-called taxi tests instead. The term " taxiing " means the movement of an aircraft on the ground under its own power.

It was intended to transport the shuttle during the subsequent phases of the ALT program in a method is referred to as piggyback drag. In this case, the transported aircraft is mounted onto the top of the transport plane. Due to the enormous total weight of this compound - in particular provided there was to load the Enterprise for the later test flights - and their high center of gravity had NASA engineers expressed the fear that the landing gear of the Boeing 747 will the forces not withstanding, the on -off and landing it interacted. Therefore, technicians installed a variety of instruments on the nose wheel of the SCA to measure the loads on the axle. In addition, the engineers wanted to study aerodynamic characteristics of the vehicle combination, in particular to control the flow behavior to the control surfaces for periodic oscillations, which are referred to as a buffet.

The rolling tests should also show how the use of the piggyback trailer combination was. The targets included the study of acceleration and braking dynamics, the procedure is given to the push to achieve a take-off speed, and the response of the different rudder for flight control.

Using a special lifting crane, the Mate - demate device, the shuttle was mounted on the back of the SCA. At the rear, there was already wearing a cowl to improve the aerodynamic characteristics of the vehicle combination, which should also wear it with most subsequent flights. On the main runway at Edwards Air Force Base, SCA accelerated at the first attempt to 78 knots ( about 144 km / h), the second at 122 knots (about 226 km / h ), and finally at 137 knots (about 254 km / h). [Note 1] The taxi test revealed no significant problems.

Coupled flights ( Captive Flights)

Three days after the rolling experiments, the SCA raised for the first time with the Enterprise onto his back. This was the first of eight flights, in which the space shuttle remained coupled to landing on the aircraft carrier ( Captive Flights). With all the space shuttle carried the aerodynamic fairing.

Captive -Inert Flights

The first five coupled flights were mainly used to collect flight data. One challenge was to mark out the boundaries of the so-called flight envelope within which a safe flight - would be possible and a successful separation of the shuttle from the SCA - despite the impact of the control surfaces during flight maneuvers possible flutter and the like. In addition, the load on the coupling between the two aircraft to be tested. Finally, the studies should show that discontinuation of separation would be possible. All necessary measurements could be made by the SCA from. Therefore, the space shuttle was disabled and unmanned, which is why these flights as a captive - inert Flights ( German as: coupled - inactive flights) are summarized.

On February 18, 1977, the team of Boeing 747 lifted and space shuttle prototype of runway 04 at Edwards Air Force Base for its maiden flight from and climbed to an altitude of about 16,000 feet (about 4,877 m) above sea level. [ Note 2], where it led at a speed of 250 knots (about 463 km / h ) various flight maneuvers to verify the response, for example, to flutter. After that, the airspeed indicator calibrated and executed maneuvers to control the stability and steerability in different altitudes using an accompanying aircraft. Finally, the landing configuration was tested with landing gear and flaps in approximately 7,300 feet (about 2,225 m) altitude. After 2 hours and 5 minutes, the team sat back down on the runway.

During the next four flights SCA graduated with the shuttle on its back similar tests at higher speeds and in ever greater heights. The last brought the team on 2 March 1977 and to about 30,100 feet (about 9,174 m) above sea level.

The captive - inert Flights demonstrated that the SCA was able to carry the shuttle up to the desired height and fly all the maneuvers required for separation. They also showed that the team in the event of a termination of separation again could land safely. This was also demonstrated that the SCA his later main task was grown, space shuttles to transport them to their space missions from the landing site back to the Kennedy Space Center.

Captive -Active Flights

During the flights the next test phase, the orbiter was activated and had a crew on board, which was not separated from the SCA ( Captive -Active Flights). However, preparations were made ​​to decouple it in an emergency situation, from the SCA. It was originally planned to conduct five captive -active flights, but after the completion of the captive - inert Flights, the test phase was restructured: Flight No. 2 has been deleted, the funds earmarked for these flight tests were added to the test program from Flight No. 1. Before Flight # 1 an additional flight was - by the numeral 1A - carried out low altitude. Through him doubts should be resolved at a tail could a so-called Hard Over occur a sudden, involuntary, full impact of a rudder. The flights numbered 4 and 5 should only be performed if problems would occur in the other flights that further investigation could appear necessary. The Captive -Active Flights should prepare the following free flights. The goals counted to verify the calculated requirements for a separation of space shuttle and SCA to test the control systems of the enterprise and carry out test runs of different procedures aboard the Space Shuttle.

The first flight (No. 1A) showed the functionality of the flight control systems at low altitude and at low speed. At about 180 knots ( 335 km / h) causing the actuation of the steering and the brake flaps without problems. The second flight (No. 1) also gave satisfactory results. The team responded to control inputs from both the Enterprise and the SCA stable. With around 230 knots (about 425 km / h ) the air brakes of the space shuttle were fully extended, which led only to a small buffet. In similar tests at about 270 knots (500 km / h), the team also responded within the specified tolerances. The systems for the separation of Orbiter and carrier aircraft functioned as predicted. The third flight (No. 3) essentially served to review the requirements and procedures for decoupling. The analysis of the measured data was consistent with the results of the second flight. In addition, showed the Captive -Active Flights that the hardware and software of the Space Shuttle worked.

Free flights ( Free Flights )

Finally, five flights were carried out in which the Enterprise was separated from the SCA to demonstrate the ability of the Space Shuttle to fly a fixed -point land after a mission to land safely there. For these free flights ( Free Flights ), the Enterprise was loaded, so that their total weight rose to around 68 tons. The ballast was distributed in different ways, starting with a loading, which offered a favorable focus to more critical way. In the first three free flights, the orbiter was not wearing nor the aerodynamic fairing at the rear, with the last two flights. Thus the conditions for an approach at the end of a space mission should be adjusted as realistic as possible. The absence of the fairing aerodynamics was greatly disturbed by turbulence around the main engines, which led to significantly shorter flight times. In the first four flights, the shuttle pilots led after separation from the SCA different turning maneuvers to provide the tractability of their aircraft to the test, and then controlled the Enterprise to a runway on the bed of Rogers Dry Lake, a dry lake bed, on the Edwards Air Force Base has a variety of slopes created as landing sites in particular for test flights. It was not until the last flight ended with a landing on a concrete runway.

Maiden flight

On the morning of August 12, 1977, approximately 65,000 spectators had gathered near Edwards Air Force Base, to almost 900 members of the press and about 2,000 invited guests. Aboard the Enterprise, the astronauts Fred Haise and Gordon Fullerton were, while the SCA should be flown by pilots Fitz Fulton and Tom McMurtry, accompanied by the flight engineer Vic Horton and Skip Guidry. Around 8:00 local time clock accelerated the engines of the 747 piggyback trailer on the runway 22 until it took off. Accompanied by five T-38 fighters flew it loops over the salt flats of Rogers Dry Lake, to gain height. The decoupling was scheduled for 8:30 clock, but due to high air temperatures, the rise was delayed until the planned height. Shortly after 8:45 clock Fulton went to about 30,250 feet (about 9,220 m ) altitude in the descent flight and Haise radioed: "The Enterprise is set; thanks for the lift. " ( German: " The Enterprise is ready Thanks for the high wear ". . ) Then pressed Haise the button for the separation, the lit seven explosive charges at the connection between SCA and Space Shuttle and the Enterprise broke from its carrier aircraft. For the first time a space shuttle was in free flight. Fulton steered the SCA to the left, Haise the Enterprise to the right. Then led Haise from various flight maneuvers to test the reactions of the shuttles to control inputs. Most recently, he flew two left-hand corners of each around 90 ° and set the space shuttle from the runway 17. With a speed of about 185 knots (nearly 345 km / h ) sat on the Enterprise, and came to almost 2 miles ( about 3.7 miles) to a halt. The maiden flight of the Enterprise had lasted 5 minutes and 21 seconds.

The Space Shuttle during the second free flight, even with the engine cowling

The Enterprise coupled off in flight from the SCA

Approach and landing with no tail trim

Flight data (Overview)

The following table provides some basic data of each test at a glance again. The "max. Height " column headed is the highest point of flight relative to sea level. [Note 2]

Results

The last flight as part of the ALT program pointed to a problem with the flight control system of the Space Shuttle. This made it susceptible to Pilot Induced Oscillation, a dangerous interaction between control inputs and the behavior of the shuttle. Thanks to further research with other missiles NASA, in particular the Vought F-8 Digital Fly -by-wire, the problem was fixed before the first orbital flight. In addition, no significant deficiencies were found.

The flight behavior of the enterprise exceeded expectations even. ALT - pilot Fred Haise praised the space shuttle later:

"It handled better, in a sense piloting, than we had seen in any simulation. [ ... ] It was crisper in terms of control inputs and Selecting a new attitude in any axis and being able to hold attitude did. It was just a better handling vehicle than we'd seen in the simulations. "

" From the perspective of a pilot it was easier to handle than we had experienced this in any simulation. [ ... ] She responded crisp to control inputs or changes in attitude about any axis and could hold new attitudes better. She was just better to control than what we knew from the simulations. "

Subsequent events

Following the ALT program, the prototype underwent Enterprise a number of other tests, for example, verified its resistance to vibration. The plan to retrofit it later to a space- capable orbiters, was ultimately rejected for cost reasons, the Enterprise came to the museum.

On April 12, 1981, the Space Shuttle Columbia lifted off for the first space flight of a reusable spacecraft. This mission is considered a milestone in the history of space flight and a success that would have been unthinkable without the Approach and Landing Tests.