MLM tanks



Integrating MLM with ISS


The Nauka multi-purpose module, MLM,
for the Russian segment of ISS

The MLM multi-purpose module (a.k.a. FGB-2 or 77KML No. 17901) originated as a backup copy to the first element of the International Space Station -- the Zarya control module, which was launched in November 1998.

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An isolated view of the MLM module in deployed position. Copyright © 2012 Anatoly Zak

The MLM Nauka module at a glance:

Liftoff mass
21.2* - 20.3** tons
20.257 tons
Mass in orbit (with add-on radiator, airlock and other hardware)
24.0 tons
24.2 tons
Pressurized volume
70 cubic meters
70 cubic meters
Available volume for cargo storage
8 cubic meters
Available volume for scientific payloads
8 cubic meters
6 cubic meters
Available power supply for scientific payloads
up to 2.5 kilowatts
up to 2.5 kilowatts
Launch vehicle
Planned launch date
2013 Dec. 11*
2017 Dec. 6
Planned docking date to the Russian segment of ISS
2013 Dec. 20*
2017 Dec. 15
Docking location
13.1 meters
Solar panels span
23.9 meters

*RKK Energia as of December 2012 (20.7 tons according to other sources)

**GKNPTs Khrunichev as of December 2012


A sibling of the first station piece

The first of two sibling spacecraft -- Zarya FGB control module -- was built during the 1990s by Moscow-based GKNPTs Khrunichev under a contract with the Boeing company. Although the agreement funded only a single vehicle, Khrunichev used available spare parts and its own funds to build a backup module, in case the original spacecraft was destroyed or rendered unusable in a launch accident.

By the time the original Zarya FGB-1 had docked successfully to the Zvezda service module in July 2000, its backup module was about 65 percent ready, according to GKNPTs Khrunichev. At that point, Russian space officials considered several potential new roles for the remaining spacecraft in the ISS program, including its use as a heavy supply ship for the Russian segment of the station.

In mid-2000, Boeing announced that it had partnered with Khrunichev to "commercialize" the FGB-2. The move put Khrunichev/Boeing team on a collision course with RKK Energia and Spacehab, who at the end of 1999 claimed the same docking port on the ISS (nadir or Earth-facing docking port on the Zarya module) for their commercial Enterprise module. In the end, none of the two projects had materialized.

A new role for FGB-2

Published: 2001 August 10

During 2001, in an effort to save money on the virtually stalled development of the Russian segment of the International Space Station, GKNPTs Khrunichev proposed to use the FGB-2 spacecraft as a base for the Universal Docking Module, USM. The USM would serve as a hub for up to three Russian research modules; however, work on the USM module all but stopped due to lack of funds.

The concept of using the FGB-2 as a Universal Docking Module had been considered in previous years, however the amount of work required for modifying the module for the task would have not justify the effort. For example, the transfer compartment on FGB-2 had to be repositioned and equipped with three additional docking ports to receive future science modules. However by 2001, Khrunichev officials argued that in light of the financial situation at the time, Russia had no chance of building any of its science modules during the station lifetime.

According to Khrunichev, it would be enough to add a single docking port to the FGB-2 in order for it to serve as the Universal Docking Module. In August 2001, Khrunichev and RKK Energia -- the main Russian contractor on the ISS -- reportedly agreed on the use of the FGB-2 as the Universal Docking Module.

According to that plan, the FGB-2 module would dock to the Earth-facing (nadir) port on the Zvezda service module, i.e. the same port where the UDM module was expected to reside. Such a configuration would leave the "nadir" port on the Zarya module for the RKK Energia's proposed Enterprise module.

In addition to the new docking port, the FGB-2's solar panels and a number of other systems would have to be modified, in order for the spacecraft to serve as a replacement for the UDM.

Khrunichev representatives said that the FGB-2 could be prepared for launch within two years after a decision on its mission had been made. From around 2001 and until 2004, the launch of the FGB-2 module to the ISS was scheduled for 2007.

Multipurpose Laboratory Module, MLM

Around 2004, it was proposed to convert the FGB-2 module into the Multi-Purpose Laboratory Module, MLM, or 77KML, according to its industrial designation. At the time, it was expected to dock the spacecraft to the nadir port of the Zarya FGB module. In order to have enough clearance during berthing with the Zarya, the front active docking port of the MLM was to be installed on a special extension adapter. According to the same plan, the MLM module would be followed to the ISS by a research module, which would be docked at the nadir port of the Zvezda Service Module. However this plan was eventually re-worked.

On July 31, 2006, the Federal space agency, Roskosmos issued a Decision No. AP-99 "On the clarification of the technical design and the work order of the multi-purpose module (MLM)."

On November 3, 2006, RKK Energia and the Russian space agency, Roskosmos, signed a contract calling for the development of the Multipurpose Laboratory Module, MLM. At the time, work on the module was expected to start in 2007, and its launch was targeted for 2009.

In the new configuration, the MLM module would accommodate service systems for the Russian Segment of the ISS and scientific payloads. The European-built ERA manipulator and the DMS-R multi-function computer would also be installed onboard. A special automated airlock for moving payloads from the interior of the station to the vacuum of space would be installed on the lower section of MLM.

To be delivered into space by the Proton rocket, the module would have an initial mass of 20,700 kilograms and provide 70 cubic meters of pressurized volume. Around eight cubic meters would be available for cargo storage and the same volume would be left for the installation of the scientific payloads. The module would sport a total of 12 workstations for various instruments and experiments. Special incubators and vibration-protected platforms for sensitive material-science research would be available.

Prior to the MLM launch, the Docking Compartment-1, which had occupied the nadir (Earth-facing) docking port of the Zvezda service module, was to be discarded along with a departing Progress cargo ship. It would then be directed to the Earth atmosphere to burn up. The MLM would then use its own engines to rendezvous with the station and dock to the freed nadir port on Zvezda.

Around a year or two after the MLM arrival at the station, a 4,000-kilogram ball-shaped Node Module would be docked to the outer end of the MLM, enabling the addition of as many as five spacecraft to the Russian segment of the ISS.

On November 9, 2007, the Collegium of the Federal space agency issued an order No. 22p "On the implementation of the Russian Segment program for the International space station in 2008-2015." The document called for a two-phase construction of the Russian Segment, where the first phase would be concluded with the addition and outfitting of the MLM module. The second phase would include the addition of the Node Module and the Science and Power Module, NEM.

MLM Development

By the beginning of 2008, the launch date of the MLM slipped from 2009 to 2011. Until May 2009, the MLM was promised to take off in December 2011. During the May 29 press-conference at the mission control in Korolev, Aleksei Krasnov, the head of manned space flight at Roskosmos said that launch was expected in the first quarter of 2012. However in the October 2009 NASA schedule, the mission was still marked for launch in December 2011.

In August 2011, the Director General of GKNPTs Khrunichev, Vladimir Nesterov, said that a prototype of the MLM module designed for electrical tests would be delivered to RKK Energia before the end of the month, despite technical issues associated with changes in the module's design documentation. (503) Around the same time, industry sources said that an integrated prototype of the MLM module had already been delivered to RKK Energia and was in process of being hooked up to the integrated prototype of the Russian segment.

By the fall of 2011, the launch of the module was postponed from December 2012 to June 2013, as the earliest. By 2012, the launch slipped further to 2014.

Work in 2012-2014

By the end of August 2012, GKNPTs Khrunichev completed the installation of the ERA robotic arm and onboard cable lines on the MLM module. The thermal control, hydraulics and pneumatic systems had been tested and solar panels had been installed, the company announced on September 3.

On September 21, GKNPTs Khrunichev completed assembly of the payload section for the MLM mission, including the module itself, its protective fairing and an adapter ring designed to serve as an interface between the spacecraft and the Proton launch vehicle. The operation would test all mechanical interfaces, check electrical systems and pneumatic pushers, the company announced. This work would be followed by the weighing of the module and vacuum tests.

A fully assembled flight version of the module would then be shipped to RKK Energia for further electrical tests, GKNPTs Khrunichev said. As of the beginning of September, the transfer of the spacecraft to RKK Energia was promised to take place in October, or two months behind a previous schedule, however it had to be delayed even further.

A critical transfer from the Moscow's district of Fili to Korolev started on the night from December 6 to December 7, 2012. From December 7 to December 14, a joint team of specialists from GKNPTs Khrunichev and RKK Energia unloaded the module from a railway car and installed it at the processing site in the main hall of the RKK Energia's Checkout and Testing Building, KIS, the company announced. According to RKK Energia, the upcoming work included autonomous and integrated tests of the module, including joint trials with ground equivalents of other Russian ISS modules as well as Progress and Soyuz transport ships. The MLM module was christened Nauka a Russian word for "science."

According to a schedule approved by RKK Energia leadership on October 24, 2012, the launch of the MLM Nauka module was scheduled for Dec. 11, 2013, enabling a docking of the spacecraft to the Zvezda Service Module on the Russian segment of the station nine days later. However according to industry sources at the time, MLM was not likely to lift off before 2014.

2013: MLM module faces lengthy delays


During 2013, the launch of the MLM module was re-scheduled to April and then to June 2014. In the meantime, tests of the MLM at RKK Energia revealed a leaking fueling valve in the propulsion system of the spacecraft. The damage was serious enough to require a complex procedure of cutting away the valve and welding in a new one. Before committing to the repairs, engineers had to practice it on a full-scale prototype of the MLM module known in Russian as Kompleksny Stend, KS.

2014: From bad to worse

On Jan. 10, 2014, the head of RKK Energia Vitaly Lopota told the official ITAR-TASS news agency that the MLM module had been returned to GKNPTs Khrunichev on Dec. 31, 2013. Lopota promised that the repair schedule for the spacecraft would be issued by the end of the month. However only in April, Lopota was able to estimate that fixing all the damage to the crippled module would take no less than nine months, while its exact processing schedule would not be set until the end of the month. By that time, the launch of the MLM in 2015 was practically ruled out. To save at least some time, plans were made to ship the MLM from GKNPTs Khrunichev directly to the launch site, letting RKK Energia to conduct all final tests of the spacecraft in Baikonur, instead of its testing facility in Korolev, near Moscow.

On April 26, a poster on the web forum of the Novosti Kosmonavtiki magazine reported that the new development schedule had been approved, targeting February 2017 for the launch of the module. The tanks of the spacecraft were found to be unaffected by the contamination, however almost all propellant lines running on the exterior of the module would have to be replaced. Moreover, the module's engines had already exceeded their warranty and had to be replaced as well. The manufacturing of the new propulsion systems would take up to eight months, the poster said.

With its central position in the architecture of the Russian segment, the MLM's troubles also stall the launch of all subsequent Russian components of the station, including the Node Module, UM, (already under construction) and the NEM laboratory and power supply module, whose full-scale development started in 2012.

Given such a prolonged delay, combined with worsening political relations between Russia and its partners in the ISS project, the questions were raised whether the MLM module and the successive components of the Russian segment could be grounded until the assembly of the new all-Russian station in the post-ISS era. Under such a scenario, the troubled spacecraft could play a role of an early hub for the future orbital outpost. These speculations were reinforced by a statement of the Russian Vice-Prime Minister Dmitry Rogozin in 2014 that Russia would pull out from the ISS project in 2020.

2015: Some certainty

In November 2014, officials cited the launch of the MLM module to the ISS in the first quarter of 2017, however the station's flight manifest surfaced in April 2015 indicated the launch in the middle of 2017. Fortunately, by that time, the Russian space program reacquired some focus after several months of uncertainty.

As late as 2015, Roskosmos continued evaluating various schemes to separate the MLM along with the UM and NEM-1 modules from the ISS at the end of its operation to form the new outpost in the low Earth orbit.

On Dec. 30, 2015, Roskosmos awarded contract No. 351-8517/15/361 to RKK Energia for the development of a modified version of the MLM module designated MLM-U. It covered work until June 30, 2018, which would apparently include the launch of the spacecraft.

2016: Work on MLM module stalls again


An undated photo released in June 2016 shows the MLM module or its prototype at RKK Energia's Checkout and Test Station, KIS, in Korolev.

In 2016, Russian officials began identifying the MLM module as MLM-U, where "U" stood for "usovershenstvovanny" or "upgraded." These "upgrades" were never publicly detailed. The new name could refer to changes related to adapting the module for operation as a part of the future Russian space station.

According to the official schedule approved on April 14, 2016, the launch of the MLM module was set for Dec. 31, 2017, or around six months behind the previously quoted launch date.

On June 20, RKK Energia issued a press-release saying that the company completed the manufacturing and testing of some unidentified equipment for the interior of the module. At the same time, the head of RKK Energia was quoted as saying that the development of documentation and the installation of large pieces of hardware on the exterior of the spacecraft had entered the final stage.

However, as of middle of September, all the work on the assembly of the MLM module had stalled again. According to industry sources, most of replacement components for the MLM's faulty propulsion system had already been manufactured, except for the pipelines, which would have to be bent based on their particular situation on the module. Still, military quality control officers, who now certify all space industry manufacturing operations, refused to give the green light for the final assembly of the propulsion system for the MLM.

The stumbling block holding the assembly of the MLM has apparently a political nature rather than any real engineering justification. According to industry sources, the management at the military certification authority apparently ran into worsening relations with the leadership of the space industry. Ironically, it was a severe oversight on the part of the military certification officials that previously cleared the module for launch with a damaged propulsion system, industry sources charged. This time, political pressure from the top would probably be needed to move things forward, sources told

The flight version of the spacecraft currently remains at Khrunichev factory in the District of Fili in Moscow with only a partially assembled propulsion system. The official schedule still calls for the launch of the spacecraft at the end of 2017, however, in order to meet this deadline, all key systems have to be assembled and the module needs to leave Fili for Baikonur Cosmodrome in April 2017. A processing team in Baikonur will need next eight months to test and fuel the 19-ton spacecraft and prepare it for integration with its Proton rocket. According to officials close to the project, the December 2017 launch deadline could still be met, however, more likely, the MLM mission will have to be postponed for a few months into the beginning of 2018.

When discussing with European space officials the launch of the European Robotic Arm, ERA, on the MLM module, their Russian colleagues indicated that the mission had been tentatively planned for March 2018.

In a rare good news for the Russian segment of the ISS, the work on the MLM module had finally restarted by the end of 2016. This time, the MLM team had a goal of launching the spacecraft in December 2017, even though, it could require to cut the time originally allocated for the spacecraft testing.

2017: Work restarts on the MLM module

As of January 2017, the launch of the MLM module was scheduled for December 6 of the same year, followed by the docking at the ISS on Dec. 15, 2017. According to the ISS flight manifest at the time, the Progress MS-06 cargo ship was scheduled to undock from the Russian segment along with the Pirs Docking Compartment, SO1, which has occupied that location since 2001, in order to free the nadir (Earth-facing) docking port on the Zvezda Service Module, SM, for the new arrival. The Pirs module would then be deorbited and burn up in the Earth's atmosphere over the Pacific Ocean along with Progress MS-06.

Following the integration of the MLM module, on Jan. 23, 2018, the Soyuz MS-06 transport spacecraft was to undock from the zenith (sky-facing) port of the MIM2 Poisk module, make a quick fly around of the ISS and re-dock at the nadir port of the MLM, becoming the first spacecraft parking at the new module.


Sections of the payload fairing (left) for the MLM Nauka module were seen inside the spacecraft processing building at Site 254 in Baikonur during the launch campaign for the Soyuz MS-12 mission at the beginning of March 2019.


Next chapter: Tank system of the MLM module


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Key contractors in the MLM module development:

RKK Energia, Korolev
Prime contractor
GKNPTs Khrunichev, Moscow Main body manufacturing and assembly; propulsion, thermal control, fire detection and suppression systems; Proton launch vehicle

Article, photography and illustrations by Anatoly Zak; Last update: March 29, 2020

Page Editor: Alain Chabot; Edits: October 21, 2008; September 30, 2016

All rights reserved



The FGB-2 module, minus its solar panels, sits in the assembly shop at Khrunichev enterprise in Moscow in August 2001. Protective red boxes cover attitude control engines. Copyright © 2001 Anatoly Zak

The FGB-2's docking adapter in its original configuration. Additional docking ports would have to be installed on the section to adapt the module for the new role of the Universal Docking Module, UDM. By 2008, developers decided to add a special Node module to that section to enable further expansion of the Russian segment. Copyright © 2001 Anatoly Zak

The interior of the FGB-2 module viewed from the docking adapter section toward the front docking port. Copyright © 2001 Anatoly Zak


The MLM module is carried by carried by a crane at GKNPTs Khrunichev in Moscow circa 2012. Click to enlarge. Credit: GKNPTs Khrunichev


A photo released on Sept. 3, 2012 shows MLM (FGB-2) module finally getting its solar panels. Credit: GKNPTs Khrunichev



Photos released on Sept. 24, 2012, show fit checks of the FGB-2 module and its launch vehicle fairing. Credit: GKNPTs Khrunichev



The MLM Nauka module arrives at RKK Energia's Checkout and Testing Station, KIS, in Korolev on Dec. 14, 2012. Credit: RKK Energia


The MLM Nauka module during testing at RKK Energia test facility, KIS, in June 2013. Click to enlarge. Credit: RKK Energia


The development prototype, KS, of the Nauka module at RKK Energia's test facility, KIS, in Korolev in June 2013. Click to enlarge. Credit: RKK Energia


Workers at RKK Energia's experimental plant work with the European robotic arm on the development prototype, KS, of the Nauka module. Click to enlarge. Credit: RKK Energia


As of 2014, plans were made to install an Earth-watching radar on the MLM module. Credit: RKK Energia


A depiction of the MLM module circa 2014 with its folded radiator. Credit: RKK Energia