Category Energiya-Buran

Full-scale test firings

By the middle of 1980 preparations had been completed for the long-awaited inaugural test firing of a complete RD-170. Mounted on Energomash’s test-firing stand nr. 2, the engine was ignited on 25 August 1980, but shut down just 4.4 seconds later. It was only the first in a long string of setbacks for the RD-170/171. The next 15 test firings were also less than satisfactory, leading to a decision to perform the 17th test firing at a lower thrust of 600 tons. This resulted in a first successful, full-duration 150-second test firing of the RD-170 on 9 June 1981.

Subsequent test firings at the same thrust rate also produced satisfactory results, giving Energomash engineers enough confidence to move on to ground tests of the nearly identical RD-171 integrated with a Zenit first stage. These tests were carried out at the IS-102 test stand of NIIkhimmash, originally used in the 1950s for testing the first stage of the R-7 missile and later the scene of test firings of the Proton first stage and the second, third, and fourth stages of the N-1. The engine earmarked for the test (serial nr. 18) had already undergone a successful test firing at Energomash’s facilities in September 1981. Later analysis did show that a turbopump rotorblade had been damaged by particles that had somehow entered the turbopump assembly, but this was considered benign enough to press on with the test firing of the Zenit first stage on 26 June 1982. To the amazement of onlookers, the test ended in disaster near the end of its scheduled 6-second duration, when the turbopump assembly burnt through and caused a massive explosion that completely destroyed the stage and the entire test stand.

The disaster raised serious questions about the fundamental design of the RD-170/171, the more so because the test had been performed at only 600 tons of thrust rather than the nominal 740 tons. It led to the creation of an interdepartmental commission to look into the status of the RD-170 development program and consider

Energomash engine test-firing stand (source: NPO Energomash).

possible alternatives for powering the Zenit first stage and Energiya’s strap-on boosters. Headed by Valentin Likhushin, the head of Nil TP, the commission included such luminaries of the Soviet rocket industry as Arkhip Lyulka, Nikolay Kuznetsov, and also Valentin Glushko himself.

One idea, proposed by I. A. Klepikov at Energomash, was to equip each combus­tion chamber with its own, smaller turbopump assembly, transforming the RD-170 into four engines with 185 tons thrust each (hence their designation MD-185, with the “M” standing for “modular’’, because the idea was to use the engine on a variety of rockets). Actually, an order to study such an engine had already come from the Minister of General Machine Building Sergey Afanasyev as early as 11 October 1980. Wary of witnessing a repeat of the N-1 fiasco, Afanasyev had ordered to set up a complete department within Energomash to design such an engine in order to safe­guard against any major development problems with the RD-170/171. It was felt that the 2UKS experimental engine, successfully tested in 1977-1978, could serve as a prototype for the MD-185.

Another option was to use the NK-33 engines developed by the Kuznetsov design bureau (under the Ministry of the Aviation Industry) for a modified version of the N-1 rocket. Although the N-1 had been canceled before the NK-33 engines ever had a chance to fly, forty of these reusable engines had undergone an extensive series of test firings up to 1977, proving their reliability. By making small modifications to the turbopumps, Kuznetsov’s engineers had managed to uprate the NK-33’s thrust from about 170 tons to just over 200 tons, meaning that four would be sufficient to replace the RD-170. Energiya’s chief designer Boris Gubanov flew to Kuznetsov’s plant in Kuybyshev, where he was shown more than 90 such engines lying in storage.

The most radical alternative studied was to replace the Blok-A strap-ons with solid-fuel boosters. That task was assigned to NPO Iskra in Perm (chief designer Lev N. Lavrov), an organization specialized in solid-fuel motors that had already built several small solid-fuel systems for Energiya-Buran. NPO Iskra devised a plan for a 44.92 m high booster consisting of seven segments. Weighing 520 tons (460 tons of which was propellant), the booster would produce an average thrust of 1,050 tons (specific impulse 263 s) and operate for 138 seconds before separating from the core stage.

In the end, none of the three proposals was accepted. Although the MD-185 was probably the least radical alternative, research showed that it would not solve the turbopump burn-through problems as the temperature of the generator gas would be virtually the same as in the RD-170/171. A major problem with both the MD-185 and NK-33 was that they increased the total number of engines on Energiya from eight to twenty, leaving more room for failure.

One can also safely assume that Glushko had second thoughts about using the NK-33 engines. After all his efforts to erase the N-1 from history, it is hard to imagine he would have accepted using engines that had originally been built for this rocket. What’s more, in 1977 Glushko had secured a decision from the Council of Ministers to ban all work on powerful liquid-fuel rocket engines not only at Kuznetsov’s design bureau, but at any organization under the Ministry of the Aviation Industry. Understandably, Kuznetsov was not about to come to Glushko’s rescue just like that.

RD-171 in test stand (source: NPO Energomash).

One of the conditions he laid down for participating in the Energiya program was that his team be officially rehabilitated after the abrupt and humiliating cancellation of its efforts several years earlier.

It was even easier to find arguments against NPO Iskra’s solid rocket motors. Aside from the safety and ecological concerns inherent in solid-fuel rockets, the Soviet Union had no experience in building solid rocket boosters of this size. More­over, they would not have been reusable and it would have been difficult to operate them in the temperature extremes of Baykonur. It would have taken an estimated 8 years to get them ready for flight.

In fact, any of the three alternative proposals would probably have delayed the first flight of Energiya by many years and would only have added to the already soaring costs of the program. In September 1982 the interdepartmental commission decided to continue test firings of improved versions of the RD-170/171 and at the same time continue research work on the MD-185. The official investigation into the June 1982 accident had concluded that it was probably the direct result of the engine being tested in a vertical position (as opposed to the near-horizontal position for the

Energomash tests). However, Energomash engineers disagreed and believed it had been caused either by aluminum particles entering the turbopump assembly from the propellant tanks or by high vibrations of the turbopump assembly.

Among the measures taken to prevent a repeat of the accident were the instal­lation of filters to prevent particles from entering the turbopump assembly and the strengthening of certain components of the turbopump. Those efforts paid off with the first successful full-duration 142-second test firing of the RD-170 at nominal thrust (740 tons) on 31 May 1983, which by many was considered a make-or-break test for the engine. In the following months, the engine performed better and better, clearing the path for another test of the RD-171 as part of a Zenit first stage. Bearing in mind the disastrous outcome of the first such test, a commission was set up to decide if it could proceed. In October 1984 the commission gave a negative recom­mendation (even KB Yuzhnoye chief Vladimir Utkin), but that was overruled by the new Minister of General Machine Building Oleg Baklanov, who had replaced Afanasyev in the spring of 1983 and proved to be a more avid supporter of the RD-170 than his predecessor. In the end, the Zenit first stage operated flawlessly in a test firing at the refurbished IS-102 test stand of NIIkhimmash on 1 December 1984, repeating that performance at the end of the same month.

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].

The ІаипсЬ

Fueling of Energiya was completed three hours before launch and that of the LOX tanks of Buran’s ODU propulsion system at T — 2h45m. A critical point came at T — 10 minutes, when the countdown switched to automatic control. Controllers breathed a sigh of relief when the balky azimuthal alignment plate responsible for the 29 October scrub retracted as planned at T — 51 seconds. With sound suppression water gushing onto the pad, the four RD-0120 engines of the Energiya 1L rocket roared to life at T — 9.9 seconds and smoothly built up thrust, clearing the way for ignition of the four strap-on boosters at T — 3.7 seconds. With all engines at full thrust and no problems detected, Energiya-Buran slowly lifted off the pad exactly as planned at 6: 00.00 Moscow time. It was a highly emotional moment for the thousands of people who had dedicated many years of their lives to this program ever since its approval in February 1976, although the atmosphere in the nearby control bunker was said to be business-like as all eyes were focused on the perform­ance of the rocket and orbiter.

Buran clears the tower (source: www. buran. ru).

As it cleared the tower, the stack performed a 28.7° roll maneuver to place it in the proper position for ascent. For onlookers the launch proved to be rather anticli­mactic. Just seconds after clearing the launch tower, Energiya-Buran disappeared into the low cloud deck. “What a pity for the photographers,” Pravda wrote the following day. “Standing out there freezing in the steppes all night and then every­thing is over in the blink of an eye” [51].

The only persons to maintain visual contact with the vehicle after that were the crews of an An-26 weather reconnaissance plane and the MiG-25 SOTN chase plane. The task of the chase plane during launch was not only to shoot video of the stack, but also to accompany Buran to the runway in the event of a return-to-launch-site abort. Behind the controls of the chase plane, which had taken off ten minutes before launch, was LII pilot Magomed Tolboyev, accompanied by cameraman Sergey Zhadovskiy. “It’s on its way! It’s going!” Tolboyev enthusiastically radioed to the ground as the stack broke through the clouds. Somewhat later he called out: “Engine operating mode changing.’’ He was referring to a reduction in thrust of both the core stage’s RD-0120 engines (between T + 30s and T + 1m11s) and the strap-on boosters’ RD-170 engines (between T + 39s and T + 1m15s) as the rocket and orbiter passed through the phase of maximum aerodynamic pressure.

At T + 2m23.95s the four strap-ons shut down their RD-170 engines and at T + 2m25.85s separated in pairs from the core stage. The separation was clearly visible from the MiG-25, with Tolboyev reporting:

“The strap-ons have separated! They’re on their way back to the ground…

Great. We can see them falling together, in parallel.’’

Not long after separation from the rocket each pair of boosters split in two, with all four now headed back to Earth individually. The boosters were not equipped with parachute systems for this mission and crashed into the steppes some 420 km from the launch pad about 7 minutes after separation.

Not long after booster separation the MiG-25 lost sight of the stack as it moved further downrange and eventually disappeared behind the horizon. All eyes were now focused on the telemetry being received from Soviet tracking stations and relayed to TsUP near Moscow. About 3 minutes into the launch, Buran reached the point where it could no longer return to the Baykonur cosmodrome for an emergency landing. As the stack sped further towards orbit, a camera installed behind one of Buran’s cockpit windows began sending back images of the Earth. At T + 6m53s the core stage’s RD-0120 engines began slowly throttling down and eventually shut down at T + 7m47.8s. Energiya’s job done, members of the rocket team quietly shook hands beneath the table, celebrating the second successful flight of the launch vehicle in as many attempts. Now it was up to the orbiter team to finish the job. Buran was now in a theoretical —11.2 x 154.2 km orbit and, if nothing were done, would re-enter shortly afterwards.

Separation of the orbiter from the core stage took place at T + 8m02.8s at an altitude of roughly 150 km. The core stage was scheduled to re-enter the atmosphere, with fragments coming down in the Pacific some 19,500 km from the launch point. After firing its thrusters to move to a safe distance from the core stage, Buran now positioned itself for a critical burn of one of its two DOM orbital maneuvering engines to impart the 66.7 m/s of additional velocity needed to reach orbit. The burn, monitored by the easternmost Soviet ground stations as Buran headed for the Soviet – Chinese border, got underway at T + 11m28s and lasted 67 seconds.

About thirty-five minutes later, at T + 46m07s, as Buran came within range of the tracking ships Dobrovolskiy and Nedelin in the South Pacific, one of the DOM engines burned for another 40 seconds (delta-V of 41.7m/s) to place the orbiter into its final 247 x 255 km orbit. Inclination was 51.6°, the same as that of the Mir space station, but the two were in different orbital planes. Since this was a conservative two – orbit test flight, there was no need for Buran to further increase its orbital altitude.

Although Soviet media did not carry the launch live, both Radio Moscow World Service and the Soviet domestic Mayak radio station reported the launch at the very beginning of their 3: 00 gmt newscasts. The World Service even optimistically said Buran had been placed into orbit, although orbital insertion was still at least ten minutes away. At 4: 10 gmt Mayak broadcast a recorded live report of the launch from its reporters both at Baykonur and in Mission Control in Kaliningrad. Moscow television showed the first footage of the launch 1.5 hours after blast-off. The TASS news agency issued the following official statement on the launch:

“On 15 November 1988 at 6.00 Moscow Time the Soviet Union launched the

universal rocket space transportation system Energiya with the reusable ship

Buran. At 6.47 the orbital ship went into the planned orbit. The test program envisages a two-orbit flight of the orbital ship around the Earth and a landing in automatic mode at the Baykonur cosmodrome at 9.25 Moscow time.”

Orbiter IK (Buran)

After returning from its mission on 15 November 1988, the 1K orbiter was sent back to the MIK OK orbiter-processing facility for post-flight inspections. Those were interrupted in early May 1989 for test flights with the An-225 Mriya carrier aircraft, staged from the Yubileynyy runway. This was in preparation for the long flight to the Paris Air Show the following month (see Chapter 4). In late June 1989 Mriya returned Buran back to Baykonur. The pair made one last demonstration flight over

Buran at the MIK OK in 1997 (B. Vis).

Baykonur on 12 April 1991 as part of an air parade to mark the 30th anniversary of the flight of Yuriy Gagarin. Later that year Soviet space officials discussed the possibility of bringing Mriya and Buran to the International Aerospace Convention in Huntsville, Alabama in July 1992, but those plans were never realized [45].

As it turned out, the demonstration flight in April 1991 had been the last time that 1K ever took to the skies. In early 1990 Western reports claimed vehicle 1K had been retired from flight status. As it had been built without a life support system, full avionics systems, and a fuel cell electrical system, it was considered too costly and difficult to modify the vehicle for a future useful unmanned or manned flight [46]. Another reason given for the grounding of vehicle 1K was that design changes had been introduced in the newer airframes under construction at the Tushino Machine Building Factory that would be too expensive to incorporate into the older vehicle. Moreover, the Soviet policy apparently was that each airframe had a lifetime of 10 years, no matter how many flights it made. With construction of 1K having started in 1983, the ship was nearing the end of its warranty [47]. However, given the astro­nomical cost of building an orbiter, it is hard to imagine that the Russians would have strictly adhered to this policy. In fact, vehicle 1K still figured prominently in the Mir – 2 assembly plans outlined in late 1991. The reported retirement of the first flight vehicle may have had more to do with the increasingly bleak prospects for the program than anything else.

For years, Buran languished in the thermal protection system bay of the MIK OK, only to be shown to occasional visitors. In 1994 the idea arose to save it from oblivion by mating it with an Energiya rocket for permanent display at the MIK RN Energiya assembly building. Since it was considered that the stack should resemble the real thing as much as possible, the intention was to attach Buran to flightworthy Energiya hardware mothballed at the MIK RN—namely, the core stage of vehicle 2L and the strap-on boosters originally earmarked for vehicle 3L. However, in the mid – 1990s a decision was made to remove the RD-170 engines from the strap-on boosters for vehicles 3L to 6L and ship them back to Energomash to be modified for use on Zenit-3SL rockets being built under the Sea Launch program. Finally, Buran was moved to high bay 4 of the MIK RN in July 1998 and assembled the following month with a non-flight rated Energiya consisting of the core stage of vehicle 5S1 and the strap-ons of vehicle 4M-KS [48].

As if its fate wasn’t sad enough, Russia’s only flown shuttle was reduced to scrap when the roof covering the three high bays of the MIK RN collapsed on 12 May 2002. The accident claimed the lives of seven men conducting repairs on the leaky roof. It was blamed on a combination of factors that had made the roof 1.5 times heavier than specified. First, the roof insulation material used during the construction of the MIK back in the 1960s was heavier than it should have been. Second, the roof had absorbed several days’ worth of heavy rains, and, third, more than 10 tons of new roofing material had accumulated on the building in preparation for the repairs. The collapse destroyed not only orbiter 1K, but also the other Energiya hardware remain-

Remains of Buran after the roof collapse (source: www. buran. ru).

ing in the MIK: three core stages and two Blok-Ya launch pad adapters in high bay 3, eight strap-on boosters in high bay 4, and another eight strap-ons in high bay 5 [49].

Orbiter 2K (“Buran-2”)

The second spaceworthy orbiter 2K (sometimes called “Buran-2”, airframe nr. 1.02) arrived at Baykonur atop a VM-T carrier aircraft on 23 March 1988. Because of the relatively limited lifting capability of the VM-T, vehicle 2K arrived at the cosmo­drome underweight and in a relatively “raw” state, with a lot of work still remaining to be done before its first flight. The Mir/Soyuz docking mission planned for 2K was

2K orbiter (front) and OK-MT mock-up in storage inside the MZK (source: Sergey Kazak/ Novosti kosmonavtiki).

much more challenging than the conservative two-orbit test flight of vehicle IK. Because of that the ship needed to be outfitted with systems that had not been on the original orbiter, such as a partially operational life support system, fuel cells, a fully operational payload bay door actuation system, a docking mechanism, and a remote manipulator arm. The vehicle was also equipped with a single ejection seat and several non-ejection seats.

On 16 May 1991 vehicle 2K, attached to the 4M core stage and strap-ons, was rolled out to Energiya-Buran pad 37 for two weeks of tests. The roll-out was witnessed by the crew of Soyuz TM-12 (Artsebarskiy, Krikalyov, Sharman), who were making final preparations for their mission. One obvious external sign that the ship wasn’t quite ready for flight yet was that many of its heat-resistant tiles were still missing. Among the work done at the pad were load tests of the fuel cells and orbiter evacuation exercises. On 30 May the stack trundled back to the MIK RN to be prepared for three days of tests at the Dynamic Test Stand (7 June-10 June 1991). After that it once again returned to the MIK RN, where vehicle 2K was detached from the core stage and returned to the MIK OK [50].

Speaking at the International Astronautical Federation Congress in Montreal in October 1991, Yuriy Semyonov told reporters that the Energiya rocket for the Buran – 2 mission had been placed on the launch pad in preparation for a 10-15 second static test firing of its main engines, and there is some evidence that Energiya 3L did undergo such a test that year [51].

By the time the Energiya-Buran program was canceled, the 2K orbiter was said to be 95-97 percent ready. The vehicle was later moved from the MIK OK to the defunct Assembly and Fueling Facility (MZK), where it still resides today.

11K55

The 11K55 was a lighter version of Zenit conceived jointly by KB Yuzhnoye and the Omsk-based PO Polyot in 1976. In its original design it had a modified Zenit first stage with a smaller propellant load and a two-chamber version of the RD-170. The newly developed second stage would be powered by a cluster of three LOX/kerosene 11D58M engines of NPO Energiya’s Blok-DM upper stage. With a launch mass of 210 tons, the rocket had a payload capacity of roughly 5 tons. The 11K55 was seen as an environmentally clean replacement for the Kosmos-3M and Tsiklon launch vehicles, rockets with storable propellants built at Polyot and Yuzhnoye, respectively. Launches were to take place from Plesetsk and Kapustin Yar. Other engines con­sidered for use on the 11K55 in the late 1980s/early 1990s were a cluster of three or four RD-120K engines on the first stage and two different re-ignitable LOX/kerosene engines for the second stage, the RD-133 and RD-134, both with a vacuum thrust of 35 tons. The 11K55 is known to have been the subject of a government decree in 1986 [69].

11K37

In 1976 KB Yuzhnoye also began looking at heavier versions of Zenit. One idea was to build a 5.4m diameter first stage with two RD-171 engines, but this was deemed unrealistic because it required new manufacturing techniques and untested transpor­tation methods by road, water, or air. Instead, planners concentrated on rockets with

two, three, or four Zenit first stages clustered together, capable of putting between about 30 and 60 tons into low orbit. The common designator for these boosters was 11K37.

The most thoroughly studied version was the one with three Zenit first stages. Mounted above that would have been a second stage with a 214-ton thrust single­chamber version of the RD-170 engine known as RD-141 as well as an RD-8 vernier engine. A later idea was to equip the stage with three 90-ton thrust RD-142 engines and several verniers. The RD-142 was apparently an improved version of the RD-120 engine used in the second stage of the 11K77. With the latter second stage, the 11K37 would have been capable of putting 40 tons into low orbit, 35 tons into polar orbit, and about 5 tons into geostationary orbit. Upper stages studied by Yuzhnoye for the 11K37 were an interorbital space tug originally developed for deployment from Buran as well as the Vikhr cryogenic upper stage.

As mentioned earlier, the 11K37 was proposed by KB Yuzhnoye in a com­petition started in 1984 to develop boosters in the 30-60 ton range, with the other candidates being Groza and an upgraded Proton rocket. A major disadvantage of the 11K37 was that it required the construction of a new launch facility. Therefore, the Ministry of General Machine Building recommended in the late 1980s to make the rocket compatible with Energiya’s UKSS launch pad at Baykonur. When a new competition was launched in the early 1990s to develop rockets in the 20-40 ton payload range, the 11K37 was still in the running, but eventually lost out to Energiya – M in 1991 [70].

The manned spacecraft tender

Throughout 2000-2005 RKK Energiya funded Kliper exclusively with its own means. Prospects for government funding emerged in October 2005 when an advanced manned transportation system was approved for development under Russia’s Federal Space Program for 2006-2015. Under new government rules, the Russian Space Agency launched a tender between three companies in November 2005 to build the ship. Requirements were for the spacecraft to be at least 80 percent reusable and fly at least 20 missions, carry up to six people, and have a cargo capacity of at least 500 kg up and down. The maiden flight should take place in 2013. Vying for the contract—apart from RKK Energiya—were NPO Molniya with an adapted version of its air-launched MAKS system and the Khrunichev Center with Angara-launched capsule-type vehicles derived from its TKS spacecraft.

Kliper spacecraft (source: www. buran. ru).

In its tender proposal RKK Energiya portrayed Kliper as one step in a multi – phased architecture for Russia’s piloted space program until 2030. In this vision Kliper would be preceded by a cardinally modernized Soyuz incorporating many elements of Kliper and succeeded by piloted Moon and Mars ships using a combination of Soyuz and Kliper technology. By now only the winged version of Kliper was eyed, because that would offer more comfortable re-entry and landing conditions for the many paying passengers (including tourists) that were expected to fly on the vehicle to return at least some of the development cost. The VA’s crew module was now cylindrically shaped with different seating arrangements.

Under the new plans Kliper was to be developed in two versions, one primarily intended for long solo missions and the other for flights to ISS. The first would be a partially reusable vehicle consisting of the VA and ABO plus the launch escape adapter. The other would be a fully reusable spacecraft made up of just the VA and the launch escape adapter with its solid-fuel engines, which after a nominal launch would stay attached to the VA to perform the deorbit burn. The ABO would be made redundant by a reusable space tug called Parom (“Ferry”) that would pick up Kliper after launch, tow it to ISS, and later return it back to a lower orbit for retrofire. Parom is a 12.5-ton space tug permanently stationed in orbit that can tow both Kliper vehicles and unmanned cargo containers to ISS. Differing in mass (14 tons vs. 12.5 tons), the two versions of Kliper would be launched by different versions of the upgraded Soyuz launch vehicle known as Soyuz-3 (for the solo version) and Soyuz-2-3 (for the ISS version). Payload capacity up and down would be 500 kg for both [17].

SPACEPLANE STUDIES AT THE ZHUKOVSKIY ACADEMY

Winged spacecraft were not only studied at spacecraft and aviation design bureaus, they were also the subject of academic studies by the original Air Force cosmonauts during the 1960s. In September 1961 most of the cosmonauts of the original “Gagarin group’’ began studying at the prestigious Zhukovskiy Academy in Moscow to improve their engineering skills in preparation for future space missions. In 1964 they were joined by the five women who had been selected for cosmonaut training in 1962. The culmination of the studies would be a thesis in a chosen field of specializa­tion that the candidates would defend before their tutors in written and oral sessions at the end of their course.

Rather than pick a completely different subject for each candidate, it was decided that all would work on one general theme. In 1965 Sergey Korolyov recommended that the cosmonauts should study a practical design for a winged reusable spacecraft, a suggestion that was accepted by the cosmonauts’ supervisor Professor Sergey Belotserkovskiy. Fifteen cosmonauts were involved in the thesis work: Yuriy Gagarin, Gherman Titov, Andrian Nikolayev, Pavel Popovich, Valeriy Bykovskiy, Aleksey Leonov, Boris Volynov, Yevgeniy Khrunov, Georgiy Shonin, Viktor Gorbatko, Dmitriy Zaikin, Valentina Tereshkova, Irina Solovyova, Tatyana Kuznetsova, and Zhanna Yorkina. Each of them was given the liberty of choosing from a series of topics suggested by their tutors. Gagarin, for instance, decided to focus on aerodynamics during approach and landing, Nikolayev on aerodynamics at hypersonic and supersonic speeds as well as on thermal protection, Titov on emergency escape systems, Popovich on engine design, Khrunov on orientation systems, Bykovskiy on fuel supply, etc.

By mid-1966 the cosmonauts had picked a lifting body shape somewhat reminiscent of the M2F1 “flying bathtub’’ that NASA had been testing at Edwards Air Force Base since 1963. The vehicle would have small wings that would only be

image33

Lifting body studied at the Zhukovskiy Academy (source: www. buran. ru).

image34

Gagarin practicing landings in a simulator.

image35

Gagarin and fellow cosmonauts examining an unidentified spaceplane model.

unfolded for the final approach and landing. In order to improve stability at super­sonic speeds, the cosmonauts decided to add small lattice wings to the nose section similar to the ones used in the emergency escape system of the Soyuz launch vehicle.

Part of the work was to test wooden scale models of the spaceplane in wind tunnels and also to practice landings on a crude simulator using primitive analog computers. The tutors followed the cosmonauts’ work with due scrutiny and their critical remarks were not always easily accepted by national heroes like Gagarin. In the autumn of 1967 Gagarin’s thesis failed to pass a critical review because the vehicle had poor gliding characteristics during the final phase of the flight. Gagarin’s solution to the problem, namely to land the spaceplane by parachute, was deemed unaccept­able. It took Gagarin several more weeks of theoretical and simulator work to refine the design such that the ship could make an unpowered runway landing.

Most of the cosmonauts defended their thesis projects in January 1968. Gagarin’s turn came on 17 February 1968, only weeks before he died in a plane crash. All of them graduated from the Academy with the diploma of “Pilot-Engineer – Cosmonaut”. Only Gorbatko’s thesis got the result “good” rather than “excellent”.

As it turned out later, this was not because his thesis was worse than the others’, but simply because it was felt not all of them should have the same result. Gorbatko, as one of the unflown cosmonauts at the time, had the misfortune of being picked as the “victim” [30].

The cosmonauts’ spaceplane studies were considered top secret, as was all diploma work at the Zhukovskiy Academy for that matter. Professor Belotserkov – skiy was not even allowed to take snapshots of his pupils, but used a hidden camera nevertheless to record their activities [31]. After having been safely hidden in a safe for almost twenty years, many of them were eventually published in 1986 in a book called “Gagarin’s Thesis’’ [32]. However, even that provided little solid information on the diploma work and did not contain a single proper picture of the spaceplane. This had to wait until another publication by Belotserkovskiy in 1992, where the spaceplane was nicknamed “Buran-68’’ [33]. There is also a famous picture released in the 1970s showing Gagarin and several other cosmonauts examining a model of a delta-wing spaceplane, but that is not “Buran-68”. Belotserkovskiy claims it is Dyna-Soar, but it clearly is not that either. Some have questioned the authenticity of the picture, but the model in question has recently been seen at the Zhukovskiy Academy.

Research on the diploma project coincided with early work on the Spiral system, but as yet there is no evidence of any interaction between Mikoyan’s team in Dubna and the Air Force cosmonauts, although Titov began training for the Spiral program in 1966-1967 and must have been aware of the project’s details. Although the finished thesis projects were sent to Lozino-Lozinkiy’s team, there are no indications that they in any way influenced the design of Spiral or future spaceplanes [34].

The OS-120 Shuttle copy

This was a virtual carbon copy of the US Space Shuttle, namely a delta-wing orbiter with three LOX/LH2 main engines in the back and strapped to the side of an external

image47

The OS-120 orbiter (source: www. buran. ru).

fuel tank. Sadovskiy’s team even went as far as studying the use of large solid-fuel rockets. Sadovskiy was no newcomer to solids, having earlier headed the develop­ment of two large solid-fuel nuclear missiles (the RT-1 and RT-2), the only such rockets ever built at the Korolyov bureau. This may even have been the very reason he was placed in charge of shuttle development at NPO Energiya.

However, the idea to use solids was abandoned because of the absence of the necessary industrial basis for the development of large solid-fuel rockets and the equipment to transport the loaded boosters to the launch site. Also, it would have been difficult to operate the boosters in the temperature extremes of Baykonur. Still, the idea to use solids was briefly reconsidered in the early 1980s as the RD-170 suffered serious development problems (see Chapter 6).

Instead, it was decided to use four 40.75 m high LOX/kerosene strap-ons, each powered by a single RD-123 engine. The orbiter itself would be fitted with three RD-0120 LOX/LH2 engines with a vacuum thrust of 250 tons. The orbital maneuver­ing system engines and reaction control system thrusters were arranged almost identically as on the US Orbiter (in two aft pods and a forward module) and would also use hypergolic propellants, the only difference being that the fuel on the Soviet vehicle would be dimethyl hydrazine rather than monomethyl hydrazine. The most striking novelty on the Soviet vehicle was the presence of two jettisonable 350-ton thrust solid-fuel escape motors on the aft fuselage that would have allowed it to instantly separate from the external tank in case of a launch accident.

The OS-120 orbiter owed its name to its 120-ton mass, which was the launch mass with a full 30-ton payload and minus the 35-ton emergency escape system, jettisoned

in the course of the launch. The overall launch mass of the stack would have been about 2,380 tons, almost 400 tons more than that of the Space Shuttle. In order to match the payload capacity of the Space Shuttle, the combined thrust of the engines was about 75 tons higher. This was also needed to compensate for the relatively high latitude of Baykonur (45°), where rockets benefit less from the Earth’s eastward rotation than they do from Cape Canaveral (28°). Had the OS-120 been launched from Cape Canaveral, it would have exceeded the Shuttle’s payload capacity by more than 5 tons for launches into 28° inclination orbits.

Being virtually identical to the Space Shuttle, the OS-120 inherited many of its drawbacks. While the LOX/kerosene engines of the strap-on boosters could be tested in flight on the 11K77 medium-lift rocket, the cryogenic engines were going to have to be tested with the priceless orbiter in place from the very first flight. With the spectacular N-1 failures still fresh in their memories, this was not an attractive idea to the Soviet planners. Therefore, they considered testing the engines in flight by mounting them on an unmanned payload canister replacing the orbiter (similar to the American Shuttle-C configuration), but this was a costly plan. The location of the main engines also shifted the vehicle’s center of gravity to the aft, imposing significant restrictions on the payloads it could carry and their distribution over the payload bay. It would also place higher acoustic loads on the orbiter, making it necessary to strengthen its structure, and also worsened the vehicle’s aerodynamic characteristics.

The OS-120 design also posed problems specific to the Soviet situation. If the engines were going to be on the orbiter, they would have to be made reusable, making their development even more challenging than it already was for an industry with very limited experience in cryogenic engine technology. Perhaps even more signifi­cantly, the orbiter would be so heavy that it could not be transported by any of the aircraft available at the time. The only aircraft capable of doing so, the Antonov design bureau’s An-124 “Ruslan”, was only on the drawing boards and years away from its first flight. Such an aircraft would also be needed for atmospheric drop tests, similar to the ones performed by NASA with Enterprise and a modified Boeing 747 [55].

LANDING GEAR AND DRAG CHUTES

Buran’s landing gear was arranged conventionally, consisting of a nose landing gear and left and right main gear. All three gear wells were covered by one door each (as opposed to the two doors on the Orbiter’s nose gear). Each gear was actuated by a single hydraulic cylinder. If the hydraulic systems failed, there was a back-up pro­cedure to deploy the gears pyrotechnically. The wheels, two on each gear, were about twice as light as similarly loaded wheels on aircraft thanks to the use of tubeless tires made from natural rubber and beryllium brake disks. Because of the heat that accumulates in the brakes during roll-out, the main landing gear wheels were cooled with nitrogen gas right after the completion of the landing roll-out. During long missions the landing gear was maintained at the proper temperature by electric heaters and also by circulating hydraulic fluid through it.

BTS-002 atmospheric test model with drag chutes deployed (source: www. buran. ru).

Buran as well as the BTS-002 atmospheric test vehicle were equipped with drag chutes to relieve the stress on the brakes and reduce the landing roll-out distance by 500 m. Stored in a container under the vertical stabilizer, the drag chutes were automatically activated by a pyrotechnic system as soon as the main landing gear touched the runway. The three chutes (each having an area of 25 m2) were extracted by three small pilot chutes and then jettisoned once the speed had been reduced to 50 km/h. Heaters and thermal protection ensured that the temperatures inside the parachute compartment did not drop below — 50°C in orbit and did not exceed + 100°C during re-entry [11]. NASA originally also planned to have drag chutes for the Orbiter flight tests, but deleted them in 1974 because it was reasoned that the lakebed runways at Edwards Air Force Base were more than long enough. However, they were eventually introduced on Endeavour in 1992 and later installed on the other Orbiters as well.

Layout

Because of the absence of main engines, the layout of the aft part of Buran’s on-orbit propulsion system differed from that of the Shuttle Orbiter. The Shuttle’s OMS and aft RCS engines are concentrated in separate “OMS pods’’ on either side of the vertical stabilizer and are each divided into two compartments, one for the OMS and one for the aft RCS. Buran had a single pod (“Base Unit’’ or BB) for both DOM engines under the vertical stabilizer, with two Reaction Control System units (“Con­trol Engine Unit’’ or BDU) attached to either side of the aft fuselage. The left BDU (BDU-L) and right BDU (BDU-P) each had twelve primary thrusters and four verniers.

The pod housed one big LOX and one big sintin tank, two auxiliary sintin tanks (exclusively used for the Reaction Control System), and gaseous oxygen tanks (solely used for the primary thrusters). if needed, sintin could be transferred from the main tank to the auxiliary ones with a turbopump driven by gaseous oxygen. The helium tanks were immersed in the main LOX tank in order to save space and cool the gas.

The forward reaction control system unit (BDU-N), situated in the nose of the vehicle, had 14 primary thrusters. Unlike the Shuttle Orbiter’s forward RCS, it carried no verniers. Also installed in the BDU-N were one gaseous oxygen tank and one auxiliary sintin tank. The BDU-N was connected to the aft engine pod via several interconnect lines that allowed gaseous oxygen, sintin, and helium gas to be trans­ferred from aft to front. After the orbital phase of the mission was completed, any remaining sintin from the front auxiliary tank was transferred back to the aft main tank to satisfy center-of-gravity requirements for landing. Although the Shuttle

Orbiter has always had the capability of cross-feeding propellant between the two OMS pods, it cannot transfer propellant between the OMS pods and the forward RCS. Such an interconnect system was proposed as one of many Shuttle upgrades, but the idea was eventually shelved.