Approach and Landing Tests

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Badge of the ALT program

Under the name of approach and landing tests ( English for approach and landing tests ), short ALT , a series of experiments is summarized with which the US space agency NASA in 1977 the flight characteristics of the newly developed space shuttle Space Shuttle tested. The test object was the space shuttle prototype Enterprise (OV-101) that was not capable of space flight . In the run-up to the first space mission of a space shuttle , the tests demonstrated that the space shuttle could be steered and landed in the atmosphere. They also showed that it was possible to transport them using the Shuttle Carrier Aircraft , a modified Boeing 747 . The Dryden Flight Research Center on Edwards Air Force Base, California, was the basis for the test flights .

background

On January 31, 1977, the Enterprise reached Edwards Air Force Base on a semi-trailer

In the 1960s, NASA developed a concept for a reusable space shuttle . Unlike the rockets launched so far, it should be able to return to Earth undamaged after a space flight. Since it would be available for further missions, the costs of a space flight should be significantly reduced. The space shuttle emerged from the program . It consists of the so-called orbiter - the actual space shuttle - an external fuel tank and two solid rockets attached to the side of the tank . The latter return to earth on parachutes after take-off, the external fuel tank burns up in the atmosphere. The orbiter re-enters the atmosphere at the end of a space mission and can be landed like an airplane. In order to test this last phase in advance, among other things, the prototype Enterprise was built. Components that were not required for the ALT tests were initially saved during construction for cost reasons and should only be retrofitted later. These include, above all, the expensive main engines and the heat shield , so that the prototype was unsuitable for use in space. On January 31, 1977, he was taken from his construction site in Palmdale, California, about 60 kilometers overland to the Dryden Flight Research Center on Edwards Air Force Base . There he should demonstrate the theoretically calculated skills in reality as part of the Approach and Landing Tests .

Goal setting

The series of experiments focused on the last minutes of a space shuttle mission after the shuttle re-entered the earth's atmosphere and slid down into deeper layers of the atmosphere and its speed decreased to the subsonic range . The subject of the investigations was in particular the ability of the space shuttle to navigate to a runway and land there safely. The stated main objectives of the ALT program were

  • the airworthiness of the orbiter with lower speed of sound to show
  • examine the functioning of certain systems for the first orbital flight,
  • check the shuttle's ability to perform manually and automatically controlled approaches and landings,
  • also to check that the ferry was able to do this with a maximum load with different centers of gravity .

In order to provide the required evidence under the conditions that could be expected at the end of a space mission, it was planned to let the Enterprise fly and land in the atmosphere. To do this, it should be transported into the air by a large aircraft, detach itself in flight and independently head for a runway. A jumbo jet was converted into a so-called Shuttle Carrier Aircraft (SCA) as a transport aircraft. This should later also be used to transport landed shuttles from the landing site back to the Kennedy Space Center .

Crews

The two shuttle crews for the ALT program (from left to right): Gordon Fullerton , Fred Haise , Joe Engle and Richard Truly in front of the Enterprise

For the approach and landing tests , two crews of astronauts were put together for the space shuttle . The first consisted of Commandant Fred W. Haise, Jr. and Pilot Charles Gordon Fullerton . The commander of the second crew was Joe Henry Engle ; the second pilot was Richard Harrison Truly .

The crew of the SCA consisted of the pilots Fitzhugh L. Fulton, Jr. and Thomas C. McMurtry and from the flight engineers Louis Guidry, Jr. and Victor W. Horton.

procedure

overview

This complex endeavor was not attempted in one step; Instead, the ALT program was divided into several phases: First, roll tests showed the aerodynamic properties of the connection between the transport aircraft and the space shuttle on the ground. Then the team undertook several test flights; The Enterprise was initially switched off and unmanned, later it was activated and had a crew on board. Finally, the connection between the shuttle and the aircraft was also disconnected in flight, the space shuttle flew and landed separately from the aircraft.

Rolling tests (taxi tests)

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

It was intended that the shuttle would be carried during subsequent phases of the ALT program using a procedure known as piggyback towing . The transported aircraft is mounted on the top of the transport aircraft. Due to the enormous total weight of this connection - especially since the Enterprise was intended to be loaded for the later test flights - and its high center of gravity , NASA engineers had expressed concern that the landing gear of the Boeing 747 would not withstand the forces that occurred during takeoff and landing it acted. Technicians therefore installed various instruments on the SCA's nose wheel to measure the loads on the axle. In addition, the engineers wanted to examine the aerodynamic properties of the combination, in particular to check the flow behavior at the tail units for periodic vibrations, which are known as buffets .

The taxi tests were also intended to show how the piggyback was handled. The objectives included the investigation of the starting and braking dynamics, the procedure with which thrust is given in order to achieve a take-off speed, and the response behavior of the various rudders for flight control .

With the help of a special lifting crane, the Mate-Demate Device , the shuttle was mounted on the back of the SCA. At the stern, it already had an engine cowling to improve the aerodynamic properties of the combination, which it was to wear on most of the subsequent flights. On the main runway at Edwards Air Force Base, the SCA accelerated to 78 knots (approx. 144 km / h) on the first attempt  , to 122 knots (approx. 226 km / h) on the second and finally to 137 knots (approx. 254 km / h) H). The taxi tests did not reveal any major problems.

Coupled flights (captive flights)

First flight of the SCA and Enterprise combination

Three days after the taxi attempts, the SCA took off for the first time with the Enterprise on its back. This was the first of a total of eight flights in which the space shuttle remained coupled to the carrier aircraft until landing (captive flights) . In all of them, the space shuttle wore the aerodynamic engine cowling.

Captive inert flights

The first five paired flights were mainly used to collect flight data. Among other things, it was necessary to define the limits of the so-called flight envelope , within which a safe flight - despite loads on the tail units during flight maneuvers, possible flutter and the like - and whether a successful separation of the shuttle from the SCA would be possible. In addition, the load on the coupling between the two aircraft should be checked. Ultimately, the research should show that breaking off the separation would be possible. All necessary measurements could be made from the SCA. The space shuttle therefore remained deactivated and unmanned, which is why these flights are summarized as captive inert flights (German for example: coupled-inactive flights ).

On February 18, 1977, the Boeing 747 and space shuttle prototype took off from runway 04 at Edwards Air Force Base on its maiden flight and rose to an altitude of about 16,000 feet (4,877 m) above sea level. There it carried out various flight maneuvers at a speed of 250 knots (approx. 463 km / h) in order to check the response behavior, for example to flutter. Afterwards, the airspeed indicators were calibrated at different altitudes with the help of an escort aircraft and maneuvers were carried out to control stability and steerability. Most recently, the landing configuration with the landing gear and flaps extended was tested at a height of around 7,300 feet (approx. 2,225 m). After 2 hours and 5 minutes the team landed on the runway again.

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

The captive inert flights demonstrated that the SCA was able to carry the shuttle to the desired height and to fly all the maneuvers required for separation. They also showed that the team could land safely again in the event of the separation. This also proved that the SCA was up to its later main task of transporting space shuttles from the landing site back to the Kennedy Space Center after their space missions .

Captive-Active Flights

During the flights of the next test phase, the orbiter was activated and had a crew on board, but was not separated from the SCA (Captive-Active Flights) . However, preparations have been made to uncouple him from the SCA in an emergency. It was originally planned to carry out five captive-active flights , but after the completion of the captive-inert flights , the test phase was restructured: flight no.2 was canceled, the attempts intended for this flight were added to the test program of flight no.1. Before flight no. 1, an additional flight - designated number 1A - was carried out at low altitude. It was supposed to dispel concerns that a so-called hardover could occur on a tail unit , a sudden, unintentional, full impact of a rudder . The flights with numbers 4 and 5 should only be operated if problems arise on the other flights which make further investigation necessary. The captive-active flights should prepare the following free flights. One of the goals was to check the calculated specifications for a separation of the space shuttle and SCA, to test the control systems of the Enterprise and to carry out trial runs of various procedures on board the space shuttle.

The first flight (No. 1A) demonstrated the functionality of the flight control systems at low altitude and at low speed. At about 180 knots (about 335 km / h) the operation of the rudder and the airbrakes caused no problems. The second flight (No. 1) also gave satisfactory results. The team reacted stably to control inputs from both the Enterprise and the SCA. At around 230 knots (approx. 425 km / h) the airbrakes of the space shuttle were fully extended, which only resulted in a small buffet. To similar tests at around 270 knots (around 500 km / h), the team also reacted within the specified tolerances. The systems for separating the orbiter and carrier aircraft worked as predicted. The third flight (No. 3) essentially served to review the specifications and procedures for decoupling. The analysis of the measured data agreed with the results of the second flight. In addition, the captive-active flights showed that the hardware and software of the space shuttle worked.

Free flights (Free Flights)

Separation for free flight without engine cowling at the tail on October 12, 1977

In the end, five flights were carried out in which the Enterprise was separated from the SCA in order to demonstrate the ability of the space shuttle to approach a designated land point after a mission and land there safely. For these free flights (Free Flights) which was Enterprise loaded so that their total weight increased to around 68 tonnes. The ballast was distributed in different ways, starting with a load that offered the most favorable center of gravity to more critical ones . On the first three free flights, the orbiter still wore the aerodynamic engine cowling on the tail, but not on the last two flights. The aim was to simulate the conditions for an approach at the end of a space mission as realistically as possible. Due to the lack of the fairing, the aerodynamics was severely disturbed by turbulence in the area of ​​the main engines, which led to significantly shorter flight times. On the first four flights, after separating from the SCA, the shuttle pilots performed various turning maneuvers to test the maneuverability of their aircraft and then steered the Enterprise to a runway on the bed of Rogers Dry Lake , a dry lake . on which Edwards Air Force Base has created various runways as landing sites, especially for test flights. Only the last flight ended with a landing on a concrete runway.

Maiden flight

On the morning of August 12, 1977, around 65,000 spectators had gathered near Edwards Air Force Base, as well as almost 900 press representatives and around 2,000 invited guests. Astronauts Fred Haise and Gordon Fullerton were on board the Enterprise , while the SCA was to be flown by pilots Fitz Fulton and Tom McMurtry, accompanied by flight engineers Vic Horton and Skip Guidry. At around 8:00 a.m. local time, the engines of the 747 accelerated the piggyback on runway 22 until it took off. Accompanied by five T-38 fighters , it flew loops over the salt flats of Rogers Dry Lake to gain altitude. The decoupling was scheduled for 8:30 a.m., but high air temperatures delayed the ascent to the planned altitude. Shortly after 8:45 am, Fulton descended at about 30,250 feet and Haise radioed: “ The Enterprise is set; thanks for the lift. "(German:" The Enterprise is ready. Thanks for carrying it up. ") Then Haise pressed the button for the separation, which detonated seven explosive charges at the connection between the SCA and the space shuttle and released the Enterprise from its carrier aircraft. For the first time a space shuttle was in free flight. Fulton turned the SCA to the left, Haise the Enterprise to the right. Haise then carried out various flight maneuvers to test the shuttle's reactions to control inputs. Finally, he made two left turns of around 90 ° each and aligned the space shuttle with runway 17. The Enterprise touched down at a speed of around 185 knots (just under 345 km / h) and came to a halt after almost 2  miles (about 3.7 km). The Enterprise's maiden flight had taken 5 minutes and 21 seconds.

  • The Enterprise flies free shortly after separating from the SCA

  • The space shuttle on its second free flight, still with the engine cowling

  • The Enterprise decouples from the SCA in flight

  • Approach and landing without tail fairing

Flight data (overview)

The following table gives an overview of some key data for the individual tests. Those with “max. Altitude ” column gives the highest point of the flight relative to sea level.

designation date Max. height Total flight time
 Duration of
free flight 		Shuttle crew Rear fairing landing
Captive-Inert Flight 1 Feb. 18, 1977 16,000  ft (4,900  m ) 2 h 05 min - without With by SCA
Captive-Inert Flight 2 Feb 22, 1977 22,000 ft (6,700 m) 3 h 13 min - without With by SCA
Captive-Inert Flight 3 Feb 25, 1977 26,000 ft (7,900 m) 2 h 28 min - without With by SCA
Captive-Inert Flight 4 Feb 28, 1977 28,000 ft (8,500 m) 2 h 11 min - without With by SCA
Captive-Inert Flight 5 02nd Mar 1977 30,100 ft (9,200 m) 1 h 39 min - without With by SCA
Captive-Active Flight 1A June 18, 1977 15,630 ft (4,760 m) 0 h 56 min - Haise , Fullerton With by SCA
Captive-Active Flight 1 June 28, 1977 24,190 ft (7,370 m) 1 h 02 min - Engle , Truly With by SCA
Captive-Active Flight 3 July 26, 1977 30,250 ft (9,220 m) 1 h 00 min - Haise, Fullerton With by SCA
Free Flight 1 Aug 12, 1977 30,250 ft (9,220 m) 0 h 54 min 5 min 21 s Haise, Fullerton With parched lake bed
Free Flight 2 13 Sep 1977 30,600 ft (9,330 m) 0 h 55 min 5 min 28 s Engle, Truly With parched lake bed
Free Flight 3 23 Sep 1977 29,500 ft (8,990 m) 0 h 51 min 5 min 34 s Haise, Fullerton With parched lake bed
Free Flight 4 Oct 12, 1977 25,200 ft (7,680 m) 1 h 08 min 2 min 34 s Engle, Truly without parched lake bed
Free Flight 5 Oct 26, 1977 22,600 ft (6,890 m) 0 h 55 min 2 min 01 s Haise, Fullerton without concrete runway

Results

The last flight under the ALT program revealed a problem with the space shuttle's flight control system. This made it vulnerable to Pilot Induced Oscillation , a dangerous interaction between control inputs and the behavior of the shuttle. Thanks to further research with other NASA missiles, particularly the Vought F-8 with digital fly-by-wire , the problem was fixed before the first orbital flight. No other significant deficiencies were found.

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

“It handled better, in a piloting sense, 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 that attitude. It was just a better handling vehicle than we'd seen in the simulations. "

“From a pilot's point of view, it was easier to handle than we had experienced in any simulation. [...] It reacted more crisply to control inputs or changes in the attitude about any axis and was able to hold new attitudes better. It was simply easier to control than anything we knew from the simulations. "

- Fred Haise

Subsequent events

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

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

See also

literature

  • Approach and Landing Test Evaluation Team: Space Shuttle Orbiter Approach and Landing Test - Captive Active Flight Test Summary . Ed .: NASA . 1977 ( nasa.gov [PDF; 6.8 MB ; accessed on May 2, 2010] NASA interim report on Captive Active Flights ).
  • Approach and Landing Test Evaluation Team: Space Shuttle Orbiter Approach and Landing Test - Final Evaluation Report . Ed .: NASA . 1978 ( nasa.gov [PDF; 13.4 MB ; accessed on May 2, 2010] Final report from NASA on the ALT program).

Individual evidence

  1. ^ Enterprise (OV-101). NASA, accessed March 27, 2010 .
  2. ↑ NASA (Ed.): Space Shuttle Orbiter Approach and Landing Test - Final Evaluation Report . 1978, Section 1: Introduction, p. 1-1 .
  3. ↑ Two crews for the shuttle approach and landing tests (ALT). (No longer available online.) NASA , archived from the original on May 21, 2015 ; accessed on May 1, 2010 (English).
  4. ^ A b Clifford J. Lethbridge: Space Shuttle Approach and Landing Tests Fact Sheet. (No longer available online.) 1998, archived from the original on September 17, 2009 ; accessed on March 27, 2010 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / spaceline.org
  5. ^ Peter W. Merlin: Free Enterprise: Contributions of the Approach and Landing Test (ALT) Program to the Development of the Space Shuttle Orbiter . Ed .: NASA . 2006, p. 3 ( nasa.gov (PDF; 1.2 MB) [accessed on May 10, 2010]).
  6. ↑ a b c d NASA (Ed.): Space Shuttle Orbiter Approach and Landing Test - Final Evaluation Report . 1978, Section 2: Captive-Inerit Test Phase, p. 2-1 .
  7. ↑ NASA (Ed.): Space Shuttle Orbiter Approach and Landing Test - Final Evaluation Report . 1978, Appendix C: Captive-Inerit and Captive-Active Flight Descriptions, p. C-2 ff .
  8. ↑ NASA (Ed.): Space Shuttle Orbiter Approach and Landing Test - Final Evaluation Report . 1978, Section 3: Captive-Active Test Phase, p. 3-1 f .
  9. ↑ a b NASA (Ed.): Space Shuttle Orbiter Approach and Landing Test - Final Evaluation Report . 1978, Section 4: Free Flight Test Phase, p. 4-1 ff .
  10. ^ Anniversary of the first Enterprise free flight. August 12, 2002, accessed May 7, 2010 .
  11. ^ Shuttle Enterprise Free Flight. (No longer available online.) NASA, archived from the original on March 7, 2013 ; accessed on March 27, 2010 (English).
  12. ^ Karl Urban: Enterprise (OV-101). February 2, 2002, accessed March 27, 2010 .
  13. ↑ Ben Evans: Space shuttle Challenger: ten journeys into the unknown . Springer, 2007, ISBN 978-0-387-46355-1 , pp. 7 ( limited preview in Google Book Search [accessed December 21, 2010]).

Remarks

  1. ↑ This article, like most of the sources on which it is based, uses the units of measurement feet and knots commonly used in aviation for flight altitudes and speeds . Additional information in meters (m) or kilometers per hour (km / h) has been calculated and rounded and is for illustrative purposes only. The altitudes are measured relative to sea level , the airspeeds are measured relative to the surrounding air. The runways used are about 2220 feet above sea level.
  2. ↑ a b The altitudes reached during the ALT program are numbered differently in different sources. The values ​​mentioned in this article are taken from NASA's final report on the ALT program and its interim report on the captive active flights (see section Literature ). Most of the altitudes mentioned there were determined from the ground using radar . Exceptions are the flight altitudes of the captive inert flights and the heights at which the Enterprise disconnected from the SCA; both were measured barometrically from the SCA . Other sources - also other NASA documents - sometimes mention significantly different altitudes, compare for example:
    • DE Denison, KC Elchert, DJ Homan: Orbiter / Shuttle Carrier Aircraft Separation: Wind Tunnel, Simulation, and Flight Test Overview and Results . Ed .: NASA . 1980, p. 10-14, 18 f . ( nasa.gov [PDF; 5.1 MB ]).
    • Peter W. Merlin: Free Enterprise: Contributions of the Approach and Landing Test (ALT) Program to the Development of the Space Shuttle Orbiter . Ed .: NASA . 2006, p. 5 ff . ( nasa.gov [PDF; 1,2 MB ; accessed on May 10, 2010]).
    • Clifford J. Lethbridge: Space Shuttle Approach and Landing Tests Fact Sheet. (No longer available online.) 1998, archived from the original on September 17, 2009 ; accessed on March 27, 2010 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / spaceline.org