HORIZONTAL FLIGHT TESTS

Like NASA in 1977, Buran program managers considered it necessary to conduct an approach and landing test program to investigate the performance of the orbiter during the final atmospheric portion of the mission. Key objectives were to check the ability of the cosmonauts to fly Buran to a controlled landing and to demonstrate the possibility of conducting automatic landings. The Soviets referred to these tests as “Horizontal Flight Tests’’ (Gorizontalnye Lyotnye Ispytaniya or GLI).

Although the objectives of the program closely matched those of NASA’s Approach and Landing Tests (ALT) with Space Shuttle Enterprise, the Russians faced one huge obstacle. They lacked an airplane that was big enough to carry an orbiter piggyback for drop tests. NASA had used a Boeing-747 carrier plane to bring the Enterprise to the desired altitude, after which it was released so it could glide to a landing at Edwards Air Force Base in California. However, at the time the Russians didn’t have the Antonov An-225 Mriya available yet and were still relying on the VM-T Atlant. Atlant’s limited capability posed a serious problem for program managers. It was not able to lift a complete Buran orbiter and, in order to get off the ground, the orbiter had to be stripped of many of its systems, including the tail. It was clear that conducting an approach and landing test program the way NASA had done was virtually out of the question, although the possibility was considered, among other things by using the An-22 Antey aircraft.

Instead, it was decided that an orbiter would have to be built that could take off from a runway by itself. That was an immense challenge for designers since Buran, like the Space Shuttle Orbiter, was never designed to take off like a conventional airplane. Nevertheless, a modified vehicle was constructed that would meet the requirements. Officially named OK-GLI, it was described as an “analog” of Buran and would become commonly known as BTS-002 (or BTS-02), with BTS standing for “Big Transport Airplane’’ (Bolshoy Transportnyy Samolyot). It got the registration number CCCP-3501002.

The BTS-002 atmospheric test model (source: Timofey Prygichev).

Fuel tank in the payload bay of BTS-002 (source: www. buran. ru).

First of all, nacelles were added to the aft fuselage that would house afterburner – equipped Lyulka AL-31F turbojet engines like those that were standard on Sukhoy Su-27 jet fighters [20]. This was in addition to two Lyulka AL-31 engines without afterburners on either side of the tail section which at the time were scheduled to be installed on spaceworthy orbiters as well. But, while BTS-002 had those two engines, in the end plans to install them on the “real” orbiters were dropped (see Chapter 7). The presence of engines on the BTS also afforded longer flight times (more than 30 minutes) and consequently more time to test flying characteristics than was the case with Enterprise’s Approach and Landing Tests, which lasted no longer than 5.5 minutes.

Wind tunnel tests had to be conducted to see whether or not the addition of these engines would have any influence on the vehicle’s aerodynamics, which was deter­mined as minimal. Since BTS-002 would not be subjected to the high temperatures of re-entry, no thermal protection system was needed. Instead, foam plastic tiles were used to cover the craft. The fuel tank for the turbojet engines was placed in the otherwise empty payload bay. Maximum take-off weight was 92 tons.

Another modification needed on BTS-002 was a system to retract the landing gear shortly after take-off. Also, the nose gear strut was slightly lengthened to increase its ground angle to 4°, which was required to facilitate take-off. As a result, BTS-002’s nose was considerably higher from the ground than Buran’s.

Just like Enterprise, BTS-002 had an air data system mounted on a boom extending from the nose of the vehicle (on spaceworthy vehicles this was embedded in the heat shield for protection during re-entry). The cockpit contained work stations for a commander (RM-1), co-pilot (RM-2), and flight engineer (RM-3), although the latter was never used. The pilots wore standard flight overalls and helmets and were strapped in ejection seats designated K-36L. BTS-002 had four on-board com­puters.

The presence of the jet engines and the landing gear retraction system were the main external differences between BTS-002 and the “real” Buran. The airframe configuration was similar to that of the orbiters that were destined for space. Center of gravity and other flight dynamics criteria were deemed within acceptable limits.

The BTS-002 pilots trained extensively for the missions on a wide variety of “flying laboratories” and also in the PRSO-1 and PDST simulators at NPO Molniya. All in all, during training sessions, the crews spent about 3,200 hours in the flight simulators, which given the eventual success of the flights clearly paid off [21].

In 1983 BTS-002 was transported by barge from the Tushino Machine Building Factory to Zhukovskiy, where it underwent further testing in a newly built facility at the premises of EMZ [22]. The approach and landing tests took place at the neighbor­ing Flight Research Institute. Before the flights started, the infrastructure consisting of beacons, radars, and transponders was modified to make it similar in set-up to that of the Yubileynyy field at the Baykonur cosmodrome. In late 1984, all was set for the first tests. Whereas NASA had conducted a relatively short program consisting of only five flights between August and October 1977, the Ministry of the Aviation Industry took one small step at a time [23].

As was common practice when new airplanes were tested in the Soviet Union, the flights were preceded by a number of taxi tests and take-off runs with increasing speeds. During most or all of the flights the crew flew two approach trajectories. First, they would descend to an altitude of some 15 to 20 m and then take the vehicle back to an altitude of 4,000 m for a second approach. On each flight BTS-002 was escorted by one or two airplanes. In all, four different chase planes were used during the tests: the L-39, Tu-134, Su-17, and MiG-25-SOTN.

This is an overview of all the ground runs and landing tests:

Ground run Date: 29 December 1984

Crew: Volk-Stankyavichus Duration: 5 minutes (14: 30-14: 35) (Moscow time)

During this first short taxi test, a maximum speed of between 40 and 45 km/h was reached, after which BTS-002 was subjected to a series of full-scale equipment tests.

Ground run Date: 2 August 1985

Crew: Volk-Stankyavichus Duration: 14 minutes (18: 56-19: 10)

During this second ground run the crew conducted two take-off runs down the runway. During the first one they tested the nose gear steering system at speeds of 30-40 km/h and performed braking at a speed of 100 km/h. Then they turned BTS-002 around and took it to a maximum speed of 205 km/h before deploying the drag chutes.

Ground run Date: 5 October 1985

Crew: Volk-Stankyavichus Duration: 12 minutes (15: 31-15:43)

Maximum speed 270 km/h. One of the left main gear tires blew out due to skidding during braking.

Ground run Date: 15 October 1985

Crew: Volk-Stankyavichus Duration: 31 minutes (14: 44-15: 15)

With a speed of 300 km/h, Volk and Stankyavichus almost reached the minimum take-off speed and briefly lifted the nose gear into the air.

Ground run Date: 5 November 1985

Crew: Volk-Stankyavichus Duration: 12 minutes (13: 40-13: 52)

Maximum speed during this run was 170 km/h.

GLI-1 Date: 10 November 1985

Crew: Volk-Stankyavichus Duration: 12 minutes (14: 06-14: 18)

On 10 November 1985, after taking an 1,800 m run and reaching a speed of 320 km/h, BTS-002 took off from Zhukovskiy’s runway for its first flight, during which an altitude of 1,500 m and a

speed of 480 km/h were reached [24]. The flight, primarily intended to determine the craft’s stability and handling, was a complete success, and upon their return Volk and Stankyavichus were greeted by their colleagues and ground crews in the traditional Soviet test-pilot way: by being tossed in a blanket. After that it was back to business with a debriefing by a commission of the Ministry of the Aviation Industry, headed by LII chief A. D. Mironov. Such debriefings would take place after each of the subsequent flights.

GLI-2 Date: 3 January 1986

Crew: Volk-Stankyavichus Duration: 36 minutes (14: 19-14:55)

Second “general” test flight. A speed of 520 km/h was reached while the analog climbed to an altitude of 3,000 m. As had been done on the first flight, a conventional 3 degree glideslope was used and BTS-002 was manually brought back to the runway.

Ground run Date: 26 April 1986

Crew: Levchenko-Shchukin Duration: 14 minutes (15: 17-15: 31)

The second projected Buran crew conducted a ground run in preparation for its own flights on the analog. One of the right main gear tires blew out due to skidding during braking.

GLI-3 Date: 27 May 1986

Crew: Volk-Stankyavichus Duration: 23 minutes (13: 34-13: 57)

Third “general” test flight. Altitude 4,000 m, speed 540 km/h.

GLI-4 Date: 11 June 1986

Crew: Volk-Stankyavichus Duration: 22 minutes (07: 42-08: 04)

During the fourth and final “general” test flight an altitude of 4,000 m and speed of 530 km/h were reached. It was also the first flight during which the standard landing mode with a steep glideslope of about 20 degrees was worked out. All three channels needed to fly the orbiter towards landing in an automatic mode were tested sequentially. Leveling out began at approximately 500m, so the final angle of approach was only two to three degrees.

GLI-5 Date: 20 June 1986

Crew: Levchenko-Shchukin Duration: 25 minutes (07: 40-08: 05)

On the fifth flight, the crew took things one step further by simultaneously switching on all three channels needed for an automatic landing.

GLI-6 Date: 28 June 1986

Crew: Levchenko-Shchukin Duration: 23 minutes (09: 30-09: 53)

All three channels were used to make BTS-002 glide automatically to an altitude of 100 m. At that altitude, Levchenko took over the controls for final approach and landing.

GLI-7 Date: 10 December 1986

Crew: Volk-Stankyavichus Duration: 24 minutes (13: 07-13: 31)

The automatic landing system controlled BTS-002 until the final second before touchdown. At that point, Volk switched the system off and performed a manual landing.

GLI-8 Date: 23 December 1986

Crew: Volk-Stankyavichus Duration: 17 minutes (12:43-13: 00)

GLI-8 saw the first landing considered to have been automatic, although the system was switched off once the main gear had touched down. Roll-out was controlled by the pilots.

GLI-9 Date: 29 December 1986

Crew: Levchenko-Shchukin Duration: 17 minutes (12:57-13: 14)

BTS-002’s complete approach and landing took place in automatic mode from an altitude of 4,000 m until coming to a complete stop. The only thing that was still done manually was lowering the nose gear to the runway.

GLI-10 Date: 16 February 1987

Crew: Volk-Stankyavichus Duration: 28 minutes (13: 30-13: 58)

First fully automatic landing, in which the pilots didn’t undertake any action from the initiation of the approach from 4,000 m until coming to a full stop on the runway.

GLI-12 Date: 25 June 1987

Crew: Stankyavichus-Volk Duration: 19 minutes (14: 34-14: 53)

Approach and landing took place in automatic mode.

GLI-13 Date: 5 October 1987

Crew: Shchukin-Volk Duration: 21 minutes (13: 50-14: 11)

Approach and landing took place in automatic mode.

Air Force test pilots Ivan Bachurin and Aleksey Boroday were scheduled to take BTS-002 to the skies for GLI-14. But, after starting up the turbojet engines, warning lights indicated that a problem had been detected. After consultation with the test director, they decided to taxi to the runway and start a take-off run. If the engines indeed weren’t functioning the way they should after they had been throttled up, the flight would be aborted. When it turned out that the warning lights were still on, the test director scrubbed the flight and ordered Bachurin and Boroday to return to the platform. This was the only scrub in the program after the vehicle’s engines had been started up.

After the problem had been solved, the flight got a new designation and the crew got another opportunity.

GLI-14B Date: 15 October 1987

Crew: Bachurin-Boroday Duration: 19 minutes (08: 12-08: 31)

Approach and landing took place in automatic mode.

After the unmanned spaceflight of Buran, Ivan Bachurin wrote the following report on GLI-14B as part of a paper on the GLI program:

“We were informed about the upcoming flight a week in advance. We prepared for the tasks we were to perform by flying the mission profile on the simulator. After that, we made the plotting charts, divided the various tasks between the two crew members, etc.

On the eve of the flight, we attended a session of the commission that determined the readiness of the aircraft, the ground facilities and infrastructure, and the crew. The reports were all fairly straightforward and only a few ques­tions were asked. The ground facilities and the aircraft were ready, and the crew was fully prepared to perform their duties. The chairman of the commission then asked: ‘Is there a need for the commander to rehearse the flight on the Tu – 154LL?’ ‘Yes, there is.’ ‘Is the plane ready?’ ‘Yes, it is.’ ‘Then you will perform that flight after the meeting.’

We performed the rehearsal flight on the flying laboratory without any problems, completed the training in the cockpit of the analog and performed a start-up of the engines for training purposes.

We spent the night at the airfield since the flight was scheduled to take place early in the morning. We didn’t talk about the upcoming flight: we had had good discussions about that subject for a week.

In the morning, we looked out the window to check the conditions. They had forecast that the wind would pick up in strength. We washed and shaved, had breakfast and underwent a medical check-up. After that, we sat and waited for the order to go. In my mind, I went through the whole upcoming flight again. Then, after a few minutes, came the signal: ‘Everything is ready. The bus is on its way to pick you up.’ ‘OK, we’re on schedule.’ We then took our gear and left for the bus, and I felt that usual pleasant feeling of being ready to perform the flight.

On our way over to the operations building, we passed ‘Number Two’ as we called the analog amongst ourselves. Inside the building, everybody was busy with his tasks. We walked into one of the dressing rooms, and weren’t disturbed by anybody for the next 15 minutes. Then the order came: ‘The crew is to take its positions.’

We went to the steps leading up to the vehicle, where a single cameraman was recording all our activities. In the small room at the end of the steps experts helped us don our personal parachute harnesses, after which we crawled through the side hatch into the cockpit and took our seats.

By then two planes, one to escort us and the other to shoot video, reported that they were ready. We could begin.

While constantly consulting the mechanic and the Flight Experiment Control Post (FECP) we prepared and started the engines, and turned on all the ship’s systems. The engineers at the FECP supervised the commands we gave to the on­board systems and could step in at any time to assist us. In the meantime [the two] planes took off.

We disconnected the external power sources and started to taxi out to the runway. The aircraft handled well, braking was very effective. I tried to remem­ber what our altitude from the ground would be, which was unusually high.

On the runway we warmed up the engines. By then, the [two] planes took their positions in the air so that at take-off they would be flying beside us. Then, at the command of the escort plane’s pilot, we put our engines in the take-off mode, did a final check of the parameters for the engines and other systems, and began taking off. The run along the runway was steady and easily controllable. Exactly at the right speed and almost immediately after I deflected the stick, the nose wheel lifted from the ground. Then we were airborne. I reduced the deflec­tion of the stick and the plane maintained its planned climb angle.

The co-pilot in the right seat, Aleksey Boroday, reported: ‘I’m pulling up the landing gear. The temperatures of engines two and three are gradually reaching their pre-set limits.’ The commander says: ‘Do not exceed.’ The co-pilot replies: ‘The temperature is now constant.’ It is good that the pilot has the capability to

take part in the control of the ship, and is constantly ready to assist the com­mander. ‘Wheels up.’

I found that as far as stability and controllability were concerned the real ship differed little from the simulator. The aircraft ‘was tightly in our hands’.

‘You’re right on schedule,’ we were told by the pilot of the escort plane. I looked around and saw the fighter not far from us, together with a Tu-134 that was shooting video. I warned the pilot of the escort plane that I was about to carry out the standard maneuvers used in these test flights for defining flying characteristics. Also, I checked the air brake.

The altitude was the predetermined one and I turned to get to our entry point. The FECP navigation officer gave us our exact position. We reached the entry point. I switched the engines to idle and activated the automatic control unit. Very eagerly, perhaps too eagerly, ‘Number Two’ executed the desired maneuver to begin the planned descent trajectory. We kept an eye on the steep descent trajectory, the performance of the on-board systems, and the air brake. The speed was what had been calculated and the plane quickly descended to the ground. Then, the plane began to level off and ‘Number Two’ smoothly decreased its speed. The landing gear was lowered and my hand was near the plane’s control stick. The fact that we were flying in automatic mode didn’t mean that we were sitting idle. The Tu-154LL would have been ‘scattered all over the ground’ had it not been for the intervention of Aleksandr Shchukin when during one of the automatic flights the plane dived right to the ground!

The altitude decreased to 200 meters, then 100, then 50. At that point, the plane was on glideslope. ‘Thirty meters… twenty meters’, read the co-pilot. ‘Let’s go up again’. I turned off the automatic control unit and increased the engine thrust. The co-pilot closed the air brake and turned off the landing mode.

The second pass was carried out in the same sequence: in automatic mode up to full stop on the runway. ‘Altitude ten… five… three, two, one meter… contact!’, reported the pilot of the escort plane. ‘Drag chute deployed’, the co­pilot confirmed.

Roll-out was steady and we had no more than a two-meter deviation from the runway’s centerline. The fighter that had served as the escort plane finished its activities with a beautiful zoom climb.

Lowering the nose wheel was smooth and the braking on the wheels was effective. Jettisoning of the parachute occurred at the right speed. ‘Number Two’ rolled to a stop. We taxied in for parking and after turning off the engines we left our seats and disembarked via the steps to the platform. Technicians and en­gineers came to the plane, and I looked with gratitude to those who had spent many hours the previous night preparing ‘Number Two’ for flight.

Finally, we gave our report and the flight was analysed. At the end of that debriefing the test director announced the date for the next flight’’ [25].

Subsequent flights simulated situations where a returning orbiter would not be at the ideal point when the final approach maneuvers were initiated. For this, the crew

would bring BTS-002 to different altitudes, or fly at speeds or in directions that differed from the calculated flight paths. In all cases, the control system corrected the deviations and brought the vehicle safely back to the runway.

GLI-19 Date: 12 March 1988

Crew: Boroday-Bachurin Duration: 21 minutes

Approach and landing took place in automatic mode.

GLI-20 Date: 23 March 1988

Crew: Boroday-Bachurin Duration: 21 minutes

Approach and landing took place in automatic mode.

GLI-21 Date: 28 March 1988

Crew: Boroday-Bachurin Duration: 22 minutes

Approach and landing took place in automatic mode.

GLI-22 Date: 2 April 1988

Crew: Stankyavichus-Shchukin Duration: 20 minutes

Approach and landing took place in automatic mode.

GLI-23 Date: 8 April 1988

Crew: Shchukin-Stankyavichus Duration: 21 minutes

Approach and landing took place in automatic mode.

GLI-24 Date: 15 April 1988

Crew: Volk-Stankyavichus Duration: 19 minutes

Final flight in the GLI program. Approach and landing took place in automatic mode.

With this, the first phase of the approach and landing tests was completed, but plans were drawn up for follow-on test flights. In March 1988 the Council of Chief Designers ordered the possibility of including NPO Energiya engineers in future BTS-002 crews to be studied, but it appears this option was not seriously considered. A later plan called for 13 more flights with pilots from both LII and GKNII. After the deaths of Levchenko and Shchukin in August 1988, LII proposed two crews consisting of Volk-Tolboyev and Stankyavichus-Zabolotskiy. Those two teams would fly the bulk of the missions, while the GKNII pilots would get just three or four flights [26].

In late 1989 Volk declared that he was still expecting to participate in the new series of BTS flights [27]. A first ground run to kick off the new phase was conducted by Rimantas Stankyavichus and Viktor Zabolotskiy, who had already been training for a possible Soyuz “warm-up flight”. During the test BTS-002 blew both tires of its right main landing gear.

Ground run Date: 28 December 1989

Crew: Stankyavichus-Zabolotskiy Duration: Unknown

Many years later Igor Volk would explain that this had been “an attempt [by Lozino-Lozinskiy] to renew the program. But, unfortunately, after the program had been stopped for a year and a half, it appeared they needed to correct many things and they stopped again” [28]. One source claims there were two more take-off runs on 23 November and 6 December 1990 just to keep BTS-002 in working order [29]. However, BTS-002 would never fly again. Still, all 24 flights had taken place without encountering any significant problems and played an important role in paving the way for Buran’s first orbital missions [30].