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BURAN Orbital

Spaceship Airframe


Problems and Methodology of Automatic Landing Complex Creation

Dr. Balashov M.P.
Key problems, specific features and performances of the terminal phase of the Orbiter’s flight – its automatic controlled landing on a runway. The grounds for the necessity of developing new systems to realize automatic landing proved. Technological cycle of the process improvement is represented.

  • The solution to the problem of the Orbiter’s automatic landing was complicated by absence of crew and atmospheric airbreathing engines, as well as with the Orbiter’ comparatively poor lift-to-drag ratio. The automatic landing of the Orbiter envisaged the necessity of solving a number of principally new problems. These should be regarded as the main of them: choosing a rational set of on-board and ground-based info- and measuring systems for navigation and landing, which would feature optimal precision characteristics;
  • choosing an optimally secure scheme of cooperation between flight control and navigation systems on one hand, and Orbiter’s on-board systems on the other;
  • realization of the R&D results of systems of automatic landing complex without flying standard versions of the Orbiter;
  • organizing the cooperation of many enterprises in different industries. NPO MOLNIYA was assigned the main enterprise to provide the automatic landing. The main conditions to define specific demands for the solutions to the problems listed were: comparatively small error area for the touchdown point;
  • Absence of remote mechanical links to operate the Orbiter’s control units and systems;
  • provision of on-board systems’ secure operation both in the atmosphere and in the orbital flight;
  • correction of the on-board autonomic navigation system’s data through ground-based sources of information. provision of radio traffic through the Orbiter’s heatproof cover.

These problems and the conditions of their solving defined the landing as leading a de-orbited Orbiter, featuring a unique aerodynamic design, thermal, aerodynamic and strength limits, to the runway along the optimal trajectory without any interference of the crew in the provided there are no abnormal situations.

The Orbiter’s systems should be provided with the radio-technical info to allow the most precise corresponding to the trajectory till the moment of stopping on the runway.

Main Principles of an Automatic Non-Powered Landing

The ‘piling-up’ of errors in the navigation and piloting parameters calculated by the on-board autonomic systems causes the need in their correction via external information sources at the stage of descent from 40 km. The errors of the latter don’t depend on the flight duration. This goal is achieved using the radio-technical navigation field of ranges, radio-altimeters, and microwave heading-slope landing system.

The analysis of the structures and functions of available autonomic and radio-technical means of navigation and landing to provide automatic landing revealed the necessity to create a new type of on-board and ground equipment. Its results allowed to recommend and later cerate:

  • digital computer-based on-board automatic flight control and navigation system;
  • unique ground-based radio navigation and landing system incorporating six re-translators of range and a microwave landing system free of traditional equal-signal zones;
  • rational scheme of on-board and ground systems cooperation.

It has been considered an optimal in energy consumption and constraint conditions trajectory of the Orbiter in the mode of automatically controlled steep descent. It has included landing maneuver, landing approach from the range of 14.5 km and the altitude of 4 km, flare-out from 2.4 km and 20 m, and running till full stop. The trajectory choice was based on the following statements:

  • generating the control signals of maintaining the preset parameters of altitude, indicated airspeed, and lateral deflection which correspond to the chosen reference trajectory;
  • performing the landing approach in vertical plane in a three-slope way: the steep one of 20°, the transitive one of 10°, and the gradient one of 2°;
  • flare-out is made at a preset pitch angle along an exponential trajectory, smoothly connected with the terminal section of a gradient glide slope, and crossing the runway 1000 m from its end;
  • the control of running in the longitudinal channel is carried out against the gap between the current and estimated angular pitch rate, in lateral channel it’s made by sustaining a zero lateral deflection form the axis of the runway.

The stages of technical suggestions, preliminary and technical project creation were accompanied by a large volume of research studies and mathematical modeling. Their results found their wording in the technical specifications by NPO MOLNIYA for the units of the control system and the framework design. The altitude-and-speed parameter measuring system incorporated unique Pitot tubes extended after passing the plasma formation zone. Antenna-transmission line units provided radio traffic through the Orbiter’s heat protection cover. The information flow cable network was designed so that it was securely protected from external electromagnetic fields. The framework was checked for probable electric potential unacceptable when using a double-wire circuit. An optimal checking system obtained the info of the Orbiter systems’ condition up to a changeable unit and provided successful preliminary and flight preparation. The rational location geometry of the six ground range re-translators was built. Three of them were chosen to provide the most precise information.

Experimental Working Out of the Automatic Landing System

The technological circuit of building complicated systems, to which we may add the complex of automatic systems, to a great extent defines the features of the test procedure, which incorporates both studies and finalizing. One of the ground and flight tests tasks’ is to check each system and the entire complex for meeting the specifications and requirements in order to work out a conclusion on the probability to control the landing of a standard Orbiter automatically.

Ground studies and tests were carried out via mathematics and semi-actual modeling on the Full Scale Stand of Equipment (FSSE), flight tests were carried out on the TU-154 flying laboratory (LL-154) and BURAN Analogue (OK-ML-2-GLI), built by NPO MOLNIYA.

Conventionally the whole volume of work was divided into estimating the serviceability of both the equipment and the mathematical support. The latter defines the main part of the tests’ final stage, as the readiness of the algorithm support and the software means their error-free operation.

A session of statistic modeling including 6000 simulations was carried out to confirm the possibility of a safe landing. It used a mathematical model of an automatic landing, which comprised the mathematical models of information systems, calculating process, movement of the Orbiter, outer effects.

Statically and dynamically the characteristics of the automatic landing simulation should be similar to the Orbiter movement parameters. This similarity was confirmed with the following results:

  • 100...200 simulations on the FSSE with the effect of random disturbances;
  • 10...15 simulations on the FSSE with the imitation of determined high-intensity disturbances;
  • 60 automatic landings of the flying laboratory with the estimation of control performance;
  • not less than 7..10 automatic landings of the Analogue of Orbiter.

The volume of tests defined the sequence of verifying the mathematical model of the automatic landing:

  • estimating the dynamical and probabilistic characteristics of the information means and their errors from the data of flying laboratory and analogue plane test;
  • verification of the flight control- and navigation system mathematical model by the data of the FSSE tests, flying laboratory and analogue test flights;
  • verification of the automatic landing mode mathematical model by the data of the FSSE tests and analogue tests;
  • estimation of the analogue plane’s dynamic similarity.

Mathematical and semi-actual modeling by the enterprises, participating in the creation of the automatic landing complex, was practically made with the common mathematical imitation support. The programs, methods, and plans of tests were mutually agreed on. The unity of the tests’ organization was provided by universal computer systems.

The final stage of ground finalizing of the systems of the automatic landing complex was carried out mostly on the FSSE.

The developed mathematical models, realized on the ES and SM computer series, were of a module structure. Its separate program modules very realistically simulate particular physical systems and units of info- measuring systems (radio-altimeters, inclinometers, altimeters, accelerometers, angular speed sensors, altitude-speed parameters system etc.). The structure is combined in circuit by the models of flight dynamics and navigation.

The results of semi-actual simulation corresponded to those of mathematical simulation and later were confirmed by a minimal number of the Flying Laboratory and the Analogue flights.

At development the cockpit layout of the Flying Laboratory the designers followed the demand of its geometrical similarity to that of the Analogue and, consequently, the standard version.

The similarity of the Flying Laboratory’ dynamic characteristics to those of the Orbiter was achieved by additional installation of the Experimental Control System (ECS), side engines reversal, and the corresponding flight configuration of the plane. The ECS provides the parametric similarity of movements around the center of inertia by means of information feedback on angles, angular speeds, and accelerations. The ECS signals come to servo-actuators, which causes additional moments thus changing the plane’s dynamic characteristics.

The cycle of run through and final confirmation of the performance of the systems and the landing complex ended with the stage of horizontal flight tests of BURAN Analogue similar in flight performance to the standard version. The Analogue’s frame configuration corresponded to the standard version, mass, position of center of inertia, moments were within the tolerances for Orbiter.

Statistic estimations of the precision data of separate systems and the entire automatic landing complex, profound run through of the algorithms and software at the stages of mathematical, semi-actual, and physical flying laboratory simulations allowed to minimize the number of very expensive flights of the Analogue.

The results of the analogue tests have fully confirmed that the info-measuring systems and information support algorithms meet the desired requirements. They had a good corresponding to the results of mathematical simulation, as well as to the tests on the semi-actual stands and the flying laboratory. The dispersion of touchdown points along the runway (+ 379 ... - 252 m) happened to be considerably less than tolerated according to the specification (+ 1100 ... – 700 m). Such high characteristics might be reached only by creating a perfect on-board control system and unique landing information complex of the airfield.

The on-board flight control and navigation system is based on a digital computer. It incorporates inertial navigation system, angular speed sensors, firmly fixed accelerometers and the systems engaged in the landing problem: altitude-speed parameters measuring system, high- and low altitude radio-altimeters, radio system for navigation and landing. The ground complex for landing includes radio range-finder system of six range re-translators and a microwave radio beam system. A principally new approach to the test pilots training – introduction of Piloting Dynamic Stand for Training (PDST) fostered the success of the physical simulation stage on the flying laboratory and the analogue.

The study and development of the automatic landing complex systems without flying the standard Orbiter required the to develop principally new methods.

Methodically the verification of the mathematical models may be divided into two stages:

  • verification of the models by the results of mathematical, semi-actual , and physical modeling carried out on versatile computers, FSSE , Flying Laboratory, and experimental Orbiter;
  • comparison of the simulation results with those of the actual tests. Such an approach made it necessary to work out a considerable amount of techniques the main of them being: statistic simulation on the accuracy criterion;
  • choosing the criteria for checking the realism of the mathematical model using the similarity criteria;
  • defining the minimal amount of flight tests needed to obtain the trustworthy info.

Safe landing in poor weather conditions after an orbital flight tin the automatic control mode was made possible after analyzing and generalizing the data of actual studies and a great volume of stand- and flight tests, which verified the basic principles of the automatic landing system.

For more than ten years many hundreds of specialists from different institutes and enterprises were concentrated on solving this problem. These specialists were from NPO MOLNIYA, TsAGI, LII, NII of Avionics, TsNII of Machinery Building, NPO ENERGIA, NPO of Automatics and Instruments Development, Moscow Institute of Electro-mechanics and Automatics, Moscow MARS Design Bureau, VNIIRA, Moscow VOSKHOD Instruments Design Bureau, NIIP.

The Prospects of Further Usage of the Gained Experience

Further development of the technical and design ideas is enclosed in the MAKS Aerospace System project and envisages:

  • using a decentralized computer system to shorten the development of mathematical support and construction of computer-incorporated subsystems due to the non-parallel work;
  • introducing a satellite range-finder navigation adjusting system instead of a ground based one;
  • using no-platform inertial systems;
  • replacing the extendable Pitot tubes with body-based ones;
  • provision of Orbiter-to-ground-to-OP radio traffic at the stage of plasma formation.

Many scientific and technological achievements, including the cycle of building the automatic landing complex as a big system, may certainly be used not only for building aircraft, but also for other means of transport requiring high security and accuracy of following the desired path, maneuvering, and mooring.