Buran programme
The Buran programme, also known as the "VKK Space Orbiter programme", was a Soviet and later Russian reusable spacecraft project that began in 1974 at the Central Aerohydrodynamic Institute in Moscow and was formally suspended in 1993. In addition to being the designation for the whole Soviet/Russian reusable spacecraft project, Buran was also the name given to Orbiter K1, which completed one uncrewed spaceflight in 1988 and was the only Soviet reusable spacecraft to be launched into space. The Buran-class orbiters used the expendable Energia rocket as a launch vehicle. They are generally treated as a Soviet equivalent of the United States' Space Shuttle, but in the Buran project, only the airplane-shaped orbiter itself was theoretically reusable.
The Buran programme was started by the Soviet Union as a response to the United States Space Shuttle program. The project was the largest and the most expensive in the history of Soviet space exploration. Development work included sending BOR-5 test vehicles on multiple sub-orbital test flights, and atmospheric flights of the OK-GLI aerodynamic prototype. Buran completed one uncrewed orbital spaceflight in 1988, after which it was recovered successfully. Although the Buran class was similar in appearance to NASA's Space Shuttle orbiter, and could similarly operate as a re-entry spaceplane, its internal and functional design was distinct. For example, the main engines during launch were on the Energia rocket and were not taken into orbit by the spacecraft. Smaller rocket engines on the craft's body provided propulsion in orbit and de-orbital burns, similar to the Space Shuttle's OMS pods.
Introduction
The Buran orbital vehicle programme was developed in response to the U.S. Space Shuttle programme, which in the 1980s raised considerable concerns among the Soviet military and especially Defense Minister Dmitry Ustinov. An authoritative chronicler of the Soviet and later Russian space programmes, the academic Boris Chertok, recounts how the programme came into being.According to Chertok, after the U.S. developed its Space Shuttle programme, the Soviet military became suspicious that it could be used for military purposes, due to its enormous payload, several times that of previous U.S. launch vehicles. The Soviet government asked the TsNIIMash for an expert opinion. Lieutenant General Yuri Mozzhorin recalled that by "approximately 1965," when the Soviet Union had the 'long arm', the Soviets did not expect war "and thought it would not happen." As institute director, Mozzhorin, recalled that for a long time the institute could not envisage a civilian payload large enough to require a vehicle of that capacity.
Officially, the Buran orbital vehicle was designed for the delivery to orbit and return to Earth of spacecraft, cosmonauts, and supplies. Both Chertok and Gleb Lozino-Lozinskiy suggest that from the beginning, the programme was military in nature; however, the exact military capabilities, or intended capabilities, of the Buran programme remain classified. Commenting on the discontinuation of the programme in his interview to New Scientist, Russian cosmonaut Oleg Kotov confirms their accounts:
Like its American counterpart, the Buran orbital vehicle, when in transit from its landing sites back to the launch complex, was transported on the back of a large jet aeroplane – the Antonov An-225 Mriya transport aircraft, which was designed in part for this task and remains the largest aircraft in the world to fly multiple times. Before the Mriya was ready, the Myasishchev VM-T Atlant, a variant on the Soviet Myasishchev M-4 Molot bomber, fulfilled the same role.
History of the Buran programme
Background
The Soviet reusable space-craft programme has its roots in the very beginning of the space age, the late 1950s. The idea of Soviet reusable space flight is very old, though it was neither continuous, nor consistently organized. Before Buran, no project of the programme reached production.The idea saw its first iteration in the Burya high-altitude jet aircraft, which reached the prototype stage. Several test flights are known, before it was cancelled by order of the Central Committee. The Burya had the goal of delivering a nuclear payload, presumably to the United States, and then returning to base. The cancellation was based on a final decision to develop ICBMs. The next iteration of the idea was Zvezda from the early 1960s, which also reached a prototype stage. Decades later, another project with the same name was used as a service module for the International Space Station. After Zvezda, there was a hiatus in reusable projects until Buran.
Programme development
The development of the Buran began in the early 1970s as a response to the U.S. Space Shuttle program. Soviet officials were concerned about a perceived military threat posed by the U.S. Space Shuttle. In their opinion, the Shuttle's 30-ton payload-to-orbit capacity and, more significantly, its 15-ton payload return capacity, were a clear indication that one of its main objectives would be to place massive experimental laser weapons into orbit that could destroy enemy missiles from a distance of several thousands of kilometers. Their reasoning was that such weapons could only be effectively tested in actual space conditions and that to cut their development time and save costs it would be necessary to regularly bring them back to Earth for modifications and fine-tuning. Soviet officials were also concerned that the U.S. Space Shuttle could make a sudden dive into the atmosphere to drop bombs on Moscow.Soviet engineers were initially reluctant to design a spacecraft that looked superficially identical to the Shuttle, but subsequent wind tunnel testing showed that NASA's design was already ideal. Even though the Molniya Scientific Production Association proposed its Spiral programme design, it was rejected as being altogether dissimilar from the American shuttle design. While NPO Molniya conducted development under the lead of Gleb Lozino-Lozinskiy, the Soviet Union's Military-Industrial Commission, or VPK, was tasked with collecting all data it could on the U.S. Space Shuttle. Under the auspices of the KGB, the VPK was able to amass documentation on the American shuttle's airframe designs, design analysis software, materials, flight computer systems and propulsion systems. The KGB targeted many university research project documents and databases, including Caltech, MIT, Princeton, Stanford and others. The thoroughness of the acquisition of data was made much easier as the U.S. shuttle development was unclassified.
The construction of the shuttles began in 1980, and by 1984 the first full-scale Buran was rolled out. The first suborbital test flight of a scale-model took place as early as July 1983. As the project progressed, five additional scale-model flights were performed. A test vehicle was constructed with four jet engines mounted at the rear; this vehicle is usually referred to as OK-GLI, or as the "Buran aerodynamic analogue". The jets were used to take off from a normal landing strip, and once it reached a designated point, the engines were cut and OK-GLI glided back to land. This provided invaluable information about the handling characteristics of the Buran design, and significantly differed from the carrier plane/air drop method used by the United States and the test craft. Twenty-four test flights of OK-GLI were performed by the Gromov Flight Research Institute test pilots and researchers after which the shuttle was "worn out". The developers considered using a couple of Mil Mi-26 helicopters to "bundle" lift the Buran, but test flights with a mock-up showed how risky and impractical that was. The VM-T ferried components and the Antonov An-225 Mriya was designed and used to ferry the shuttle.
The flight and ground-testing software also required research. In 1983 the Buran developers estimated that the software development would require several thousand programmers if done with their existing methodology, and they appealed to Keldysh Institute of Applied Mathematics for assistance. It was decided to develop a new high-level "problem-oriented" programming language. Researchers at Keldysh developed two languages: PROL2 and DIPOL, as well as the development and debugging environment SAPO PROLOGUE. There was also an operating system known as Prolog Manager. Work on these languages continued beyond the end of the Buran project, with PROL2 being extended into SIPROL, and eventually all three languages developed into DRAKON which is still in use in the Russian space industry. A declassified May 1990 CIA report citing open-source intelligence material states that the software for the Buran spacecraft was written in "the French-developed programming language known as Prolog", possibly due to confusion with the name PROLOGUE.
Flight crew preparation
Until the end of the Soviet Union in 1991, seven cosmonauts were allocated to the Buran programme and trained on the OK-GLI test vehicle. All had experience as test pilots. They were: Ivan Ivanovich Bachurin, Alexei Sergeyevich Borodai, Anatoli Semyonovich Levchenko, Aleksandr Vladimirovich Shchukin, Rimantas Antanas Stankevičius, Igor Petrovich Volk and Viktor Vasiliyevich Zabolotsky.A rule, set in place for cosmonauts because of the failed Soyuz 25 of 1977, insisted that all Soviet space missions contain at least one crew member who has been to space before. In 1982, it was decided that all Buran commanders and their back-ups would occupy the third seat on a Soyuz mission, prior to their Buran spaceflight. Several people had been selected to potentially be in the first Buran crew. By 1985, it was decided that at least one of the two crew members would be a test pilot trained at the Gromov Flight Research Institute, and potential crew lists were drawn up. Only two potential Buran crew members reached space: Igor Volk, who flew in Soyuz T-12 to the space station Salyut 7, and Anatoli Levchenko who visited Mir, launching with Soyuz TM-4 and landing with Soyuz TM-3. Both of these spaceflights lasted about a week.
Levchenko died of a brain tumour the year after his orbital flight, Bachurin left the cosmonaut corps because of medical reasons, Shchukin was assigned to the back-up crew of Soyuz TM-4 and later died in a plane crash, Stankevičius was also killed in a plane crash, while Borodai and Zabolotsky remained unassigned to a Soyuz flight until the Buran programme ended.
Spaceflight of I. P. Volk
was planned to be the commander of the first crewed Buran flight. There were two purposes of the Soyuz T-12 mission, one of which was to give Volk spaceflight experience. The other purpose, seen as the more important factor, was to beat the United States and have the first spacewalk by a woman. At the time of the Soyuz T-12 mission the Buran programme was still a state secret. The appearance of Volk as a crew member caused some, including the British Interplanetary Society magazine Spaceflight, to ask why a test pilot was occupying a Soyuz seat usually reserved for researchers or foreign cosmonauts.Spaceflight of A. S. Levchenko
was planned to be the back-up commander of the first crewed Buran flight, and in March 1987 he began extensive training for his Soyuz spaceflight. In December 1987, he occupied the third seat aboard Soyuz TM-4 to Mir, and returned to Earth about a week later on Soyuz TM-3. His mission is sometimes called Mir LII-1, after the Gromov Flight Research Institute shorthand. When Levchenko died the following year, it left the back-up crew of the first Buran mission again without spaceflight experience. A Soyuz spaceflight for another potential back-up commander was sought by the Gromov Flight Research Institute, but never occurred.Ground facilities
Maintenance, launches and landings of the Buran-class orbiters were to take place at the Baikonur Cosmodrome in the Kazakh S.S.R. Several facilities at Baikonur were adapted or newly built for these purposes:- Site 110 — Used for the launch of the Buran-class orbiters. Like the assembly and processing hall at Site 112, the launch complex was originally constructed for the Soviet lunar landing programme and later converted for the Energia-Buran programme.
- Site 112 – Used for orbiter maintenance and to mate the orbiters to their Energia launchers. The main hangar at the site, called MIK RN or MIK 112, was originally built for the assembly of the N1 moon rocket. After cancellation of the N-1 programme in 1974, the facilities at Site 112 were converted for the Energia-Buran programme. It was here that Orbiter K1 was stored after the end of the Buran programme and was destroyed when the hangar roof collapsed in 2002.
- Site 251 – Used as Buran orbiter landing facility, also known as Yubileyniy Airfield. It features one runway, called 06/24, which is long and wide, paved with "Grade 600" high quality reinforced concrete. At the edge of the runway was a special mating-demating device, designed to lift an orbiter off its Antonov An-225 Mriya carrier aircraft and load it on a transporter, which would carry the orbiter to the processing building at Site 254. A purpose-built orbiter landing control facility, housed in a large multi-storey office building, was located near the runway. Yubileyniy Airfield was also used to receive heavy transport planes carrying elements of the Energia-Buran system. After the end of the Buran programme, Site 251 was abandoned but later reopened as a commercial cargo airport. Besides serving Baikonur, Kazakh authorities also use it for passenger and charter flights from Russia.
- Site 254 – Built to service the Buran-class orbiters between flights. Constructed in the 1980s as a special four-bay building, it also featured a large processing area flanked by several floors of test rooms. After cancellation of the Buran programme it was adapted for pre-launch operations of the Soyuz and Progress spacecraft.
Missions
Atmospheric test flights
An aerodynamic testbed, OK-GLI, was constructed in 1984 to test the in-flight properties of the Buran design. Unlike the American prototype, OK-GLI had four AL-31 turbofan engines fitted, meaning it was able to fly under its own power.Flight date | Mission | Shuttle | Crew | Duration | Landing Site | Notes | Sources |
10 November 1985 | OK-GLI | 2 | 00d 00h 12m | Baikonur | |||
3 January 1986 | OK-GLI | 2 | 00d 00h 36m | Baikonur | |||
27 May 1986 | OK-GLI | 2 | 00d 00h 23m | Baikonur | |||
11 June 1986 | OK-GLI | 2 | 00d 00h 22m | Baikonur | |||
20 June 1986 | OK-GLI | 2 | 00d 00h 25m | Baikonur | |||
28 June 1986 | OK-GLI | 2 | 00d 00h 23m | Baikonur | |||
10 December 1986 | OK-GLI | 2 | 00d 00h 24m | Baikonur | First automatic landing | ||
23 December 1986 | OK-GLI | 2 | 00d 00h 17m | Baikonur | |||
29 December 1986 | OK-GLI | 2 | 00d 00h 17m | Baikonur | |||
16 February 1987 | OK-GLI | 2 | 00d 00h 28m | Baikonur | |||
21 May 1987 | OK-GLI | 2 | 00d 00h 20m | Baikonur | |||
25 June 1987 | OK-GLI | 2 | 00d 00h 19m | Baikonur | |||
5 October 1987 | OK-GLI | 2 | 00d 00h 21m | Baikonur | |||
15 October 1987 | OK-GLI | 2 | 00d 00h 19m | Baikonur | |||
16 January 1988 | OK-GLI | 2 | Baikonur | ||||
24 January 1987 | OK-GLI | 2 | Baikonur | ||||
23 February 1988 | OK-GLI | 2 | 00d 00h 22m | Baikonur | |||
4 March 1988 | OK-GLI | 2 | 00d 00h 32m | Baikonur | |||
12 March 1988 | OK-GLI | 2 | Baikonur | ||||
23 March 1988 | OK-GLI | 2 | Baikonur | ||||
28 March 1988 | OK-GLI | 2 | Baikonur | ||||
2 April 1988 | OK-GLI | 2 | 00d 00h 20m | Baikonur | |||
8 April 1988 | OK-GLI | 2 | Baikonur | ||||
15 April 1988 | OK-GLI | 2 | 00d 00h 19m | Baikonur |
Orbital flight of Orbiter 1K in 1988
The only orbital launch of the Orbiter K1 Buran was at 3:00 UTC on 15 November 1988 from pad 110/37 in Baikonur. The uncrewed craft was lifted into orbit by the specially designed Energia booster rocket. The life support system was not installed and no software was installed on the CRT displays. The shuttle orbited the Earth twice in 206 minutes of flight. On its return, it performed an automated landing on the shuttle runway at Baikonur Cosmodrome.Planned flights
The planned flights for the shuttles in 1989, before the downsizing of the project and eventual cancellation, were:- 1991 — Orbiter 2K Ptichka uncrewed first flight, duration 1–2 days.
- 1992 — Orbiter 2K Ptichka uncrewed second flight, duration 7–8 days. Orbital maneuvers and space station approach test.
- 1993 — Orbiter 1K Buran uncrewed second flight, duration 15–20 days.
- 1994 — Orbiter 3K Baikal first crewed space test flight, duration of 24 hours. Craft equipped with life-support system and with two ejection seats. Crew would consist of two cosmonauts with Igor Volk as commander, and Aleksandr Ivanchenko as flight engineer.
- 1994-1995 - Second, third, fourth and fifth crewed orbital test flights.
- December 1991 — Orbiter 2K uncrewed second flight, with a duration of 7–8 days. Orbital maneuvers and space station approach test:
- * automatic docking with Mir's Kristall module
- * crew transfer from Mir to the shuttle, with testing of some of its systems in the course of twenty-four hours, including the remote manipulator
- * undocking and autonomous flight in orbit
- * docking of the crewed Soyuz-TM 101 with the shuttle
- * crew transfer from the Soyuz to the shuttle and onboard work in the course of twenty-four hours
- * automatic undocking and landing
Cancellation of the programme 1993
The programme was designed to boost national pride, carry out research, and meet technological objectives similar to those of the U.S. Space Shuttle programme, including resupply of the Mir space station, which was launched in 1986 and remained in service until 2001. When Mir was finally visited by a space shuttle, the visitor was a U.S. Shuttle, not Buran.
The Buran SO, a docking module that was to be used for rendezvous with the Mir space station, was refitted for use with the U.S. Space Shuttles during the Shuttle–Mir missions.
Baikonur hangar collapse
On 12 May 2002, a hangar roof at the Baikonur Cosmodrome in Kazakhstan collapsed because of a structural failure due to poor maintenance. The collapse killed 8 workers and destroyed one of the Buran craft, which flew the test flight in 1988, as well as a mock-up of an Energia booster rocket. It was not clear to outsiders at the time which Buran programme craft was destroyed, and the BBC reported that it was just "a model" of the orbiter. It occurred at the MIK RN/MIK 112 building at Site 112 of the Baikonur Cosmodrome, 14 years after the first and only Buran flight. Work on the roof had begun for a maintenance project, whose equipment is thought to have contributed to the collapse. Also, before the day of collapse, there had been several days of heavy rain.List of vehicles
Five orbiters were planned to be built,,"Craft, flying article", and hull numbering starts with 1 or 2, two originally ordered in 1970s and three additionally ordered in 1983.For research and testing purposes, several test articles produced, designated 1M-8M, hull numbering starts with 0.
By 1991 two operational vehicles were delivered to Baikonur, three others were under construction at Tushino.
Most of the geo-location below shows the shuttle bodies on the ground; in some cases Google Earth's History facility is required to see the shuttle within the dates specified.
Related test vehicles and models
Image | Name | Construction Date | Usage | Current status |
BOR-4 | 1982–1984 | Sub-scale model of the Spiral space plane | 1:2 scale model of Spiral space plane. 5 launches. NPO Molniya, Moscow. | |
BOR-5 | 1983–1988 | Suborbital test of 1/8 scale model of Buran | 5 launches, none were reflown but at least 4 were recovered. NPO Molniya, Moscow. | |
Wind tunnel models | Scales from 1:3 to 1:550 | 85 models built; see unnamed test article in table above. | ||
Gas dynamics models | Scales from 1:15 to 1:2700 |
Revival possibilities
Over time, several scientists looked into trying to revive the Buran programme, especially after the Space Shuttle Columbia disaster.The 2003 grounding of the U.S. Space Shuttles caused many to wonder whether the Russian Energia launcher or Buran shuttle could be brought back into service. By then, however, all of the equipment for both had fallen into disrepair or been repurposed after falling into disuse with the collapse of the Soviet Union.
In 2010 the director of Moscow's Central Machine Building Institute said the Buran project would be reviewed in the hope of restarting a similar crewed spacecraft design, with rocket test launches as soon as 2015. Russia also continues work on the PPTS but has abandoned the Kliper program, due to differences in vision with its European partners.
Due to the 2011 retirement of the American Space Shuttle and the need for STS-type craft in the meantime to complete the International Space Station, some American and Russian scientists had been mulling over plans to possibly revive the already-existing Buran shuttles in the Buran programme rather than spend money on an entirely new craft and wait for it to be fully developed but the plans did not come to fruition.
On the 25th anniversary of the Buran flight in November 2013, Oleg Ostapenko, the new head of Roscosmos, the Russian Federal Space Agency, proposed that a new heavy lift launch vehicle be built for the Russian space program. The rocket would be intended to place a payload of in a baseline low Earth orbit and is projected to be based on the Angara launch vehicle technology.
Technical description
Buran orbiter (OK - Orbitalny Korabl (rus: Орбитальный Корабль, Orbital Vehicle) ([GRAU] index 11F35)
Crew cabin
The cockpit is an all-metal welded pressurised compartment houses the crew’s workplaces, control and life support systems. It has three decks. The upper deck, Command Module, is the workspace for the crew and serves to accommodate commander, pilot, engineer and mission specialist's seats, as well as dashboard and RMS operator's workplace. The middeck is intended to place life support and auxiliary equipment Up to 6 crewmembers could be seated there during launch and reentry as well. The lower deck houses the power systems.. Retrieved 13 April 2020.
Docking system
Docking compartment, SM mounted into rear part of payload bay. It is a spherical compartment with a diameter of 2.67 m, in the upper part passes into a cylindrical tunnel with an androgynous peripheral docking unit installed on it.Unlike US Space Shuttle, docking compartment for Buran features extendable tunnel to increase clearance between orbiter and the station. Another hatch, facing to payload bay, was to support extravehicular activity from the orbiter.
Remote manipulator
SBM, similar to Space Shuttle's RMS was developed at the Central Research and Development Institute for Robotics and Technical Cybernetics to support operations with payload. It could be operated both in manual and automatic modes. Buran-class orbiter could carry, depending on the mission, one or two manipulator arms.Laboratory modules
To expand Buran's capabilities, pressurised modules, similar to ESA's Spacelab was designed based on 37K design. These modules had to be both compartments to conduct experiments and logistics volume, cold be either mounted in payload bay and connected to the crew cabin via tunnel or to be temporarily docked to Mir's Kristall's side docking port.On Buran's maiden flight, the Accessory Unit 37KB №37070 was installed into orbiter's payload bay. It carried recording equipment and accumulators providing power to onboard systems as the regular fuel cells based power system was not ready at the time.
Second 37KB №37071 was built in 1987. It was planned to build third 37KB №37072, but this was never happened because of program cancellation.
Propulsion
Orbital maneuvering is provided by Joint Propulsion System, ODUSpecifications
The mass of the Buran vehicle is quoted as 62 tons, with a maximum payload of 30 tons, for a total lift-off weight of 105 tons;Mass breakdown
- Mass of Total Structure / Landing Systems:
- Mass of Functional Systems and Propulsion:
- Maximum Payload:
- Maximum liftoff weight:
- Length:
- Wingspan:
- Height on Gear:
- Payload bay length:
- Payload bay diameter:
- Wing glove sweep: 78 degrees
- Wing sweep: 45 degrees
- Total orbital maneuvering engine thrust:
- Orbital Maneuvering Engine Specific Impulse:
- Total Maneuvering Impulse: 5 kgf-sec
- Total Reaction Control System Thrust:
- Average RCS Specific Impulse:
- Normal Maximum Propellant Load:
Buran and the US Space Shuttle
Comparison to NASA's Space Shuttle
Because Buran's debut followed that of, and because there were striking visual similarities between the two shuttle systems—a state of affairs which recalled the similarity between the Tupolev Tu-144 and Concorde supersonic airliners—many speculated that Cold War espionage played a role in the development of the Soviet shuttle. Despite remarkable external similarities, many key differences existed, which suggests that, had espionage been a factor in Buran's development, it would likely have been in the form of external photography or early airframe designs. One CIA commenter states that Buran was based on a rejected NASA design. See the section above.Key differences between Buran and NASA's Space Shuttle
- Buran had no main engines; take off and ascent trajectory were accomplished with the Energia rocket whose four main engines were expendable. The three Space Shuttle main engines were part of the orbiter, and were reused for multiple flights.
- The core Energia rocket was equipped with its own guidance, navigation, and control system – unlike Space Shuttle whose entire control system was in the orbiter.
- Unlike Space Shuttle's boosters, each of Energia's four boosters had their own guidance, navigation, and control system, which allowed them to be used as launch vehicles on their own to deliver smaller payloads than those requiring the complete Energia-Buran system.
- Energia could be configured with four, two or no boosters for payloads other than Buran, and in full configuration was able to put up to 100 metric tons into orbit. The Space Shuttle orbiter was integral to its launch system and was the system's only payload.
- Energia's four boosters used liquid propellant. The Space Shuttle's two boosters used solid propellant.
- The liquid fueled booster rockets were not constructed in segments vulnerable to leakage through O-rings, which caused the destruction of.
- The Energia rocket was not covered in foam, the shedding of which from the large fuel tank led to the destruction of.
- Energia's four boosters were designed to be recovered after each flight, though they were not recovered during Energia's two operational flights. The Space Shuttle's boosters were recovered and reused.
- Buran's equivalent of the Space Shuttle Orbital Maneuvering System used GOX/LOX/Kerosene propellant, with lower toxicity and higher performance than the Shuttle's pressure-fed monomethylhydrazine/dinitrogen tetroxide OMS engines.
- Buran was designed to be capable of both piloted and fully autonomous flight, including landing. The Space Shuttle was later retrofitted with automated landing capability, first flown 18 years after the Buran on STS-121, but the system was intended to be used only in contingencies.
- The nose landing gear was located much farther back on the fuselage rather than just under the mid-deck as with the NASA Space Shuttle.
- Buran could lift 30 metric tons into orbit in its standard configuration, comparable to the early Space Shuttle's original 27.8 metric tons
- Buran included a drag chute, the Space Shuttle originally did not, but was later retrofitted to include one.
- The lift-to-drag ratio of Buran is cited as 6.5, compared to a subsonic L/D of 4.5 for the Space Shuttle.
- Buran and Energia were moved to the launch pad horizontally on a rail transporter, and then erected and fueled at the launch site. The Space Shuttle was transported vertically on the crawler-transporter with loaded solid boosters.
- The Buran was intended to carry a crew of up to ten, the Shuttle carried up to eight in regular operation and would have carried more only in a contingency.