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BURAN Orbital

Spaceship Airframe

Creation

BURAN Orbiter Horizontal Flight Tests

General Mikoyan S.A.
Principle scheme of descent and landing approach, problems of the Guidance and Navigation Systems development are discussed. Main differences of the BURAN Analogue-Plane for the horizontal flight tests and the standard Orbital Spaceship (Orbiter) as well as ground-based equipment of airdrome are considered. The paper describes process of the crew training and the results of flight tests. It presents the recommendations for use of the Analogue-Planes and Flying Laboratories in further projects.


Principal Scheme of BURAN Orbiter Descent, Landing Approach, and Landing

The terminal phase of Orbiter’s flight is its atmosphere descent and landing on a runway. At its first flight BURAN had angle of attack of α = 39° when in upper atmosphere, then after reaching M = 12 the angle was smoothly reduced to α = 22° at M = 5, and to α = 10° at M = 2. Later the Orbiter proceeded to a simple gliding flight and finished the flight by the landing on an aerodrome.

All the descent stage down to the end of the landing is automatically controlled in the normal mode. However, when in the atmosphere the crew can switch to handle-operated or director control mode.

The on-board control system incorporating four mutually reserved (reduplicated) computers uses the data from inertial navigation system to guide the Orbiter along the trajectory needed to reach the desired area near the airfield at the height of 20 km with the velocity and heading preset. The trajectory motion in longitudinal direction is controlled by changing roll (the velocity vector-related) angle modulus with a fixed α(M) program. This guidance is to provide matching between the available flight range and required range to the airfield calculated by the navigation system.

Lateral trajectory movement is controlled via periodical reversals to change the sign of roll angle in order to maintain the heading gap (angle between velocity vector and the azimuth to the airfield) within the preset tapering limits.

After passing the stage of plasma formation the Orbiter enters the operation area of the VYMPEL system’s ground range-finder radio beacons at the height of 40…45 km. From the range data, measured by any three beacons (of the six available) the exact location of the Orbiter is calculated. The data of inertial navigation system are corrected and the corresponding data are supplied to the Orbiter’s on-board automatic flight control system as well as to the Information Displaying System (IDS) for manned flights. The Orbiter is guided by on-board systems to the area near the aerodrome referred to as Heading Adjustment Cylinder (HAC), i.e. to the turn on base leg before landing approach (from one or another end of the runway depending on the wind).

Here it enters the operation area of microwave radio beam landing system, which transmits ciphered vertical and horizontal signals for the on-board computer to calculate the trajectory of Orbiter’s safe landing on the preset runway section. In case of substantial wind change at the aerodrome a special signal of reflected landing direction may be sent to the Orbiter. This signal is transmitted before entry into the atmosphere.

Besides range finder beacons and microwave landing beacons the VYMPEL radio system incorporates long range (up to 400 km) radar, air traffic controller radar with a range of 200 km, and landing 3D-tracking radar to check the landing glide slope movement. BURAN is also equipped with a responder, which increases the ground radar’s range and transmits the altitude data from the on-board system.

The information from all the means of checking is collectively processed and displayed in a real time mode on multi directional observation- and other displays of the Mission Control Center near Moscow and the control tower at Baikonur.


BURAN Orbiter Analogue

To estimate BURAN’s performance and aerodynamics, confirm its similarity to mathematical models and stand tests’ results as well as its automatic landing probability with the preset precision the Analogue (atmospheric flight version of the Orbiter) was created (002 vehicle).

Since there was no carrier-plane available to launch the Analogue at the desired altitude (like it was in American Space Shuttle tests), the designers had to make it able to take off and gain the necessary altitude independently. So they made some improvements to the standard version.

First of all they had to install nacelles housing afterburner-equipped turbojets similar to those of Su-27 (Sukhoy) fighter in addition to the two non-afterburner turbojets enclosed in the Orbiter’s initial design to adjust the gliding trajectory (later they were removed from orbit-launched versions). This led to changes of the initial outer shape, but wind tunnel tests showed no substantial influence of the nacelles with engines running to the aerodynamics.

Besides, the motor flight capability increased the Analogue’s endurance (up to 30 minutes instead of 3...5 minutes) thus enabling to obtain far more information.

The payload bay housed fuel tank. Landing Gear (LG) retraction system was added (BURAN can only lower LG). Nose LG strut was lengthened to increase ground angle to 4° for better takeoff circumstances.

The Analogue’s airframe configuration was similar to that of the Orbiter. Mass, coordinates of the mass center and inertia moments were within tolerances for the Orbiter. Foamed plastic tiles were used instead of the TPS quartz ones.

A backup (reserved for emergency) Analogue’s control system for control surfaces was developed and installed together with its own sensors. It was supposed to be used in case of main digital control system failure (no need of its activation ever occurred at flights). Other minor changes were made.

To provide the creation of the 002 vehicle (BTS-002) special test beds were built at Experimental Machine-Building Plant (EMZ) after Myasishyev V.M. to test and develop the propulsion unit, fuel system, engine fire protection, ejection system and other devices as well as frequency test bed.

The airfield of Flight Research Institute became a test copy of that at Baikonur. Landing radar and VYMPEL microwave landing complex incorporating glide slope and azimuth beacons, and relay station of landing radio range finder were installed. The airfield’s standard air traffic control radar was used. Three navigation radio range finder beacons were placed nearby. To check and record the trajectory standard local measure facilities e.g. KAMA tracking radar and OPAL high-precision optical 3D pinpoint system were used.

The telemetry system of the Analogue also differed. There were installed two telemetry systems: one – to transmit the data of the control system and computer (about 2300 parameters), the other – to transmit the info from the sensors located in different systems and structure members of the Analogue (about 2200 parameters). Besides, about 450 parameters were recorded onboard. Engineers Teplov A.I. and Golyanitsky O.A. from NPO MOLNIYA played an important part in the development of this system.

A checking-and-measurement station (CMS) was built by the EMZ Plant after Myasishyev V.M. with a calculation center headed by Semyonov V.V. The station was to receive and process the in-flight telemetry info and to issue the permission to fly judging from the data of pre-flight check stand based on the parking site of the 002 vehicle. The center was also engaged in post-flight info processing.

Flight Experiment Control Post (FECP) was set up at the airfield. It was imitating the landing section of the Mission Control Center. It received the info from telemetry and external trajectory measurers. The info was processed by a powerful computer complex and sent real time to 12 electronic displays.

The specialists were watching them in readiness to inform the flight leader of any abnormal changes in trajectory, aerodynamic parameters, speed and altitude, systems operation. The flight leader and the navigator communicating with the pilots were to give them instructions or recommendations if necessary. They were watching the flight via navigation screen and a TV monitor displaying the picture of the aircraft through high-zoom optics or from an escort plane cam. This monitor was also used to watch the landing.

The following people played main part in building the Baikonur copy airfield equipment, securing its operation during tests: Mr. Manucharov A.A., Falkov A.I., Fillipov A.D., Vasin V.P. from the Flight Research Institute (LII). General Mikoyan S.A. (NPO MOLNIYA) was the flight leader. The LII navigators Igreykin G.G. and Korsak V.B. worked on the ground to help the pilots build the route to the experiment’s start point.

When on actual descent in the atmosphere the Orbiter glides with engines stopped. At the altitude of 20 km its nominal true airspeed should be 1870 km/h (indicated airspeed 500 km/h, M = 1.75), at about 14 km altitude the speed becomes subsonic, and by 10 km altitude the Mach number drops to about 0.8.

BURAN’s landing speed is about 310 km/h. To achieve this speed at the point of landing a gliding speed of 450...470 km/h before landing is enough. However, since the effect of headwind must be compensated, the gliding speed has to be increased by means of a steeper trajectory. Initially it was estimated as 540 km/h, but later, in adjusted calculations, reduced to 520 km/h, thus slightly reducing the slope angle and vertical speed.

The effect of head- or tail- wind might be compensated through shifting the Key Point (KP) of pre-land gliding start further or nearer from the runway. This would mean lower glide speed on a more gradient slope.

But for BURAN the KP was constant. It was entered in the flight program beforehand depending on the Orbiter’s estimated landing mass. The slope angle may vary about 17…22° and diving rate – within 50...60 m/sec (instead of 3…4°and 4…6 m/sec of ordinary engine-powered airplanes).

At the altitude of 500 m the so-called ‘first flare-out’ begins. Trajectory speed and diving rate start to drop. At about 100 m the Orbiter follows a gradient slope familiar to pilots.

At about 15 m it flares out finally and lands with a diving rate below 1 m/sec as a rule and a speed of 300...320 km/h.

When flying an ordinary airplane a pilot adjusts its slope by changing the thrust: increasing in undershoot and decreasing in overshoot. We can say that he changes its thrust -to-weight ratio. For the BURAN flight the same result may be achieved by varying its aerodynamic drag. To increase drag the rudder halves (that are used as an air break) are spread against their mid position. This changes the glide’s slope angle and flight range. Fully closed halves compensate the effect of a headwind of up to 20 m/sec according to the specifications.

When on Horizontal Flight Test the pre-land glide started from the KP 12.5 km from the runway, at the altitude of 4 km. The Analogue followed the preset trajectory. The signals from microwave landing system were transmitted to the on-board automatic control system and pilot’s instruments. Besides, the system maintained the speed by moving rudder halves, extended LG, launched the drag parachute at running, and applied wheel brakes. The landing run direction was adjusted against the heading radio beacon at the runway end.

When taking off, climbing, approaching the KP, and on the initial point of gliding, the Analogue was piloted manually, as these stages were not automated, being absent from BURAN’s real flight procedure.

In early flights the trajectory parts before the KP were used to test the Analogue’s stability, handling, aerodynamics, and performance. In all flights the Analogue was followed by a two-seat fighter, engaged in video filming and external checking. The last flights were performed with transmitting the image to the tower (the same thing was done when on real BUAN’s descending).

Each flight of the Analogue followed a session of the Ministry of Aircraft Industry’s (MAP) Board on techniques, headed by Mr. Mironov A.D., Chief of Flight Research Institute (LII).

The Board issued the conclusion about the possibility and the conditions of flight, after revising the flight mission, its stand simulation and lab flight summary, the Analogue’s readiness to fly, as well as that of the pilots and all the ground services.

The program of flight tests started similarly to ordinary planes with taxiing and simple runs at gradually increasing speed (the first taxiing took place on December 29, 1984). On the last run the Analogue was accelerated almost to its takeoff speed elevating the nose. Finally the Analogue performed its first flight on November 10, 1985. At the first landing the Analogue used the turbojets thrust, so it glided with a slope of about 3° like an ordinary airplane. Pilots Igor Volk and Rinantas Stankyavichus (from LII) were at the controls. They flew four test missions and confirmed the aircraft’s stability and good handling. Later they flew in a queue with pilots Anatoly Levchenko / Alexandre Schukin (from LII), and Ivan Bachurin / Alexey Borodai (from Air Force).

The Analogue’s conventional landing mode with a steep glide was worked out from the fourth flight. First the gliding was in the handle-operated control mode, then, channel by channel, the automatic mode was switched on. During the sixth flight the Analogue was gliding with all three channels automatic to the altitude of 100 meters. In seventh flight the automatic mode was switched off just before touchdown. In eighth – the main wheels touched the ground when in automatic. This may be regarded as the first automatic landing, though the running after was pilot-controlled (it’s the simplest stage for a pilot). In the ninth flight the landing approach from the altitude of 4 km (KP) and the landing till full stop on the runway were fully automatic except for manual depressing of the nose LG strut after landing. And at last in the tenth flight (February 16, 1987), starting from switching on the automatics at 4 km and to the full stop on the runway the pilots didn’t do any control actions. This flight is officially known as the first flight of BURAN’s Analogue with automatic landing approach (see the drawing).

After 14 flights (7 of them with automatic landing) the test pilots gained enough info to issue the test conclusion, however the seniors decided, that they make ten more flights to collect statistic data. In these flights the aircraft was intentionally lead to the KP with some deflections from nominal altitude, speed, and flight direction data which were within the pre-calculated limits at the KP. In all the cases the control system solved successfully its task and soon guided the aircraft to the preset trajectory.

With the purpose of gaining the statistics data in all the flights an approach with landing imitation was made followed by a go-round-again from an altitude of 15...20 m, and the second approach ended with landing. So, from the seventh flight there were 36 automatic landing approaches, 15 of which – with fully automatic landing and running and two – with partially manual running. In all the cases the longitudinal and lateral deflections in the touchdown point were considerably lower than limited in the specifications, and the running was practically following the runway’s axis line. The test flights ended in April 1988.

The Analogue is a very sophisticated complex of systems, based on four on-board computers programmed to control the systems and check their operation. This requires very laborious and important preparation and pre-flight check-up. For instance the final check-up under a special program with real time checking takes nearly four hours.

All the work on the Analogue’s systems employment, check-up, and flight preparation was carried out under the supervision of engineers Yayloyan N.P., Damentsev A.I., Bezhanov O.S. (EMZ), Trunov U.V., and Kirilyuk G.A. (NPO AP). The documentation on complex ground check-ups was worked out under the supervision of engineers Petrosyan N.A. and Korovin K.G. (NPO MOLNIYA).

The test flights were organized by engineers Krupnyansky E.F. (EMZ), Pospelov M.K. and Titov A.I. (NPO MOLNIYA), Complex Test Group was headed by engineer Dolgikh O.S. (EMZ).

Designer’s support, supervision for the aircraft’s preparation to tests were made by Mr. Blokhin Yu.D. and Safronov O.M. (NPO MOLNIYA). Great help was by the test participants from the Air Force Flight Test Institute, headed by Mr. Bezhevets A.S., Chernobrivtsev V.M., and Lukashov A.I., and those from the Ministry of Aircraft Industry’s Flight Research Institute, headed by Mr. Lunyakov V.S., Volkov V.K., and Solov’yov V.A.

In a sole case, when pilots I. Bachurin and A. Borodai (from Air Force) were to make their first flight, they understood after the turbojets start-up (by the warning lights) that there were some problems with the control system. The flight leader permitted them to tax on the runway to make a decision about flight after cranking the engines. When the crew reported that the warning was still on, the flight leader ordered them to head for parking. This was the only case of a cancel after the engines’ start-up.


Researches on Flying Laboratories and Piloting Stands

Even before the start of the Horizontal Flight Tests (HFT) the pilots of the special BURAN test group trained an non-powered (no-thrust) landing for several years. They performed a great deal of flights with a no-thrust landing imitation from the stratosphere flying MIG-25 ‘Fox-bats’, and the military pilots also flying TU-22M ‘Backfires’. They made hundreds of ‘flights’ on the Piloting Dynamic Stand for Training (PDST) in NPO MOLNIYA. This allowed to train under the program of HFT, including the stages of takeoff, climbing, approaching the KP, descending and running to the full stop, with the displayed outer space, terrain, runway, and its where about corresponding to those of real airfield at Zhukovsky.

‘Flying’ the stand, the pilots were also trained to coup with ‘faults’ occurring under a worked out list. The training flights from the KP at 4 km to the full stop were also carried out in the automatic mode. As a result of this work it was corrected The Orbiter’s Flight Employment Manual, prepared by the group under supervision of engineers Senchenko A.T. and Tymko H.V. (NPO MOLNIYA).

Main training flights were performed on the TU-154 Flying Laboratories (LL-154), equipped with an experimental digital computer-incorporated electric control system for control surfaces and spoilers. Co-pilot’s seat was also modified to resemble the Analogue’s pilot seat as close as possible (the pilot’s seat was occupied by the pilot of the same group to check and secure the flight by switching on the conventional control system if necessary). The spoilers and side turbojets thrust reversal were used to provide the dynamic similarity to the Orbiter, and identical thrust-to-weight ratio, whereas the variation of the middle turbojet thrust imitated the action of BURAN’s airbrake.

Prior to the pilots’ training, these airplanes were tested for the equipment serviceability, undergone flight modes, trajectories, and algorithms workout. The following specialists took an important part in development and operation securing of the flying laboratories: Mr. Berestov L.M., Chernikov L.N., Lopato Yu.V., Lyashkov B.V. (from LII), Nekrasov O.N., Getsin M.S., Tetyanets V.V. (NPO MOLNIYA), Bonk R.I. (MOKB MARS).

Profound preparation of the pilots was another feature of the flights. Each mission was first trained on the complex Full Scale Stand of Equipment (FSSE), then with the flight crew on the Piloting Dynamic Stand for Training (PDST), and before the BURAN flight, as a rule the same day, aboard the TU-154 Flying Laboratory. Preparation to the training on PDST was held by engineers Moroz A.D., Frolov V.I., Borisov Yu. A., Zherebchikov Yu.I., and others (NPO MOLNIYA).

Vital help in organizing and conducting the flight tests was by Mr. Kazakov V.A., Minister of Aircraft Industry, Dr. Vasilchenko K.K., Chief of the Flight Research Institute and Chiefs of many other Research Institutes and Design Bureaus.


Conclusion

The tests of the BURAN Analogue are unique – many things were made for the first time, prior to all – the flight of a airplane, equipped with an electric control system using computer-generated signals, with an non-powered (no-thrust) landing. The tests confirmed the correctness of the control and navigation systems’ design, their operation, and reliability. The tests secured the successful accomplishment of the BURAN’s first space flight and made a great contribution to the science and practice of the world’s aviation.

It’s obvious, that further creation of aerospace systems with the Orbiter, landing as airplane, will make it necessary to use both the Flying Laboratory and the Analogue to develop the equipment and landing systems, as well as to train the pilots. So, preliminary designing works for the MAKS Aerospace System provided the development of the SU-27 ‘Flanker’-based Flying Laboratory, as well as the Orbiter’s Analogue.