Air leak in the PrK chamber




The Zvezda Service Module, SM

When in 1993 Russia was invited to join what would become the International Space Station, it brought along an array of hardware, drastically reshaping previously envisioned look of the outpost. The most significant Russian contribution in the space station design was the service module, intended to provide life-support and living quarters for a three-member long-duration crew. The 20-ton spaccecraft would also maintain the outpost's orbit with its propulsion system; supply and distribute electrical power from its solar panels, as well as send, receive and process flight control information with its internal computers.

Previous chapter: Zarya FGB Control Module


Zvezda module at a glance:

Spacecraft designation(s) Zvezda Service Module, SM, 17KSM No. 12801
Mission Permanent component of the ISS
Docking destination ISS, Russian Segment, Zarya FGB, front port
Spacecraft mass 20.3 tons
Maximum body diamater 4.2 meters
Length 13.1 meters
Solar panels span 30 meters
Crew up to 6 people

The service module had a wingspan of 30 meters from tip to tip of its solar arrays, and it was 13.1 meters from end to end. The Service Module contained three pressurized compartments: a small, spherical Transfer Compartment, PKhO, at the forward end; the long, cylindrical main Work Compartment; and the small, cylindrical Transfer Chamber at the aft end. An unpressurized Aggregate Compartment was wrapped around the exterior of the Transfer Chamber at the aft end of the module.

The Assembly Compartment held external equipment such as propellant tanks, thrusters and communications antennas. The Integrated Propulsion System, ODU, (INSIDER CONTENT) of the service module consisted of two orbit-correction engines, KD, designated S5.79 with a thrust of 300 kilograms each and 32 small thrusters, DMT, designated 11D428A-10 and 11D428-14. They were developed at NIIMash and had a thrust of 12.5 kilograms each and designed to control the course, yaw and bank movements of the module. All these engines were fed from four tanks, with two tanks for oxidizer and two for fuel. Nitrogen gas was used for the pressurization of the tanks.

The Onboard Calculation System, BVS (from the Russian Bortovaya Vychislitelnaya Sistema), which provides overall flight control for the Zvezda Service Module, SM, and other modules docked to it. (INSIDER CONTENT)

The Service Module included four docking ports, one in the aft Transfer Chamber and three in the spherical forward Transfer Compartment -- one facing forward, one facing up and one facing down. The aft docking port had a probe and cone docking mechanism to allow docking with the Progress cargo ship and the Soyuz crew spacecraft. It also was outfitted with the automated rendezvous and docking system. (INSIDER CONTENT)

All three ports on the forward compartment had hybrid docking mechanisms to allow docking with the FGB module to the forward-facing port; with the Russian Science and Power Platform, NEP, using the "zenith" or up-facing port; and with the Russian Universal Docking Module, USM, (INSIDER CONTENT) originally using the "nadir" or down-facing port. The FGB module was launched in 1998 and docked with the Zvezda as planned in July 2000, but the two other components had never flown, even though, according to early plans, the NEP was expected to launch in January 2001, followed by the USM in April.


Aft section of the Zvezda Service Module as seen from an approaching transport vehicle.

Living accommodations on the Service Module included personal sleeping quarters for the crew; a toilet and hygiene facilities; a galley with a refrigerator-freezer; and a table for securing meals while eating. The module had a total of 14 windows, including three 9-inch diameter windows in the forward Transfer Compartment for viewing docking activities; one large 16-inch diameter window in the Working Compartment; an individual window in each crew compartment; and additional windows positioned for Earth observations. Exercise equipment included a NASA-provided treadmill and a stationary bicycle. The crew’s wastewater and condensation water was to be recycled for use in oxygen-generating devices on the module, but it was not planned to be used as drinking water.

Spacewalks using Russian Orlan-M spacesuits could be performed from the Service Module by using the Transfer Compartment, PKhO, as an airlock. The module could also will provide data, voice and television communications with Mission Control Centers in Moscow and in Houston.

The Service Module was launched on a Russian Proton booster from the Baikonur Cosmodrome, Kazakhstan. At launch, many systems were in standby. Once in orbit, pre-programmed commands onboard fully activated its systems, the solar arrays and the communications antennas were deployed. The Service Module then entered a passive flight mode for a rendezvous with the already-orbiting Zarya control module, FGB, and the Unity module, also known as Node 1. As the passive "target" vehicle, the Service Module maintained station-keeping in orbit while the Zarya/Unity stack performed the rendezvous and docking via ground control and the Russian automated rendezvous and docking system. (106)

Life-support system, SZhO (INSIDER CONTENT)

The Zvezda Service Module is equipped with a multifaceted life-support system providing air and water for the Russian crew with a high level of recycling capability.

Onboard Radio System, BRK (INSIDER CONTENT)

The radio complex aboard the Zvezda consists of several sub-systems providing data and voice communications between the station and ground control.

Control system, SUBA (INSIDER CONTENT)

The Zvezda carries around 2,700 units of avionics and related instruments with a total mass of 2.5 tons. They are interconnected by nearly 3,000 cables with a total mass of 2,990 kilograms. The management of all that hardware is conducted via the Onboard Equipment Control System, SUBA (from the Russian Sistema Upravleniya Bortovym Kompleksom).

Power-Supply System, SEP (INSIDER CONTENT)

The Power Supply System, (known by Russian abbreviation as SEP for Sistema Elektro-Pitaniya) provides direct current to all onboard systems of the Zvezda Service Module. The SEP is also designed to supply power and re-charge batteries aboard the Soyuz and Progress transport ships, as well as to feed power to other modules of the Russian ISS Segment, for the exception of the Zarya FGB. Finally, the SEP system aboard Zvezda is configured to receive extra power from the station's American Segment, which was expected to have excess capacity in its completed form, thanks to its large solar panels.

Thermal Control System, SOTR (INSIDER CONTENT)

The Thermal Control Sustem, (known by Russian abbreviation, SOTR, for Sistema Obespecheniya Teplovogo Rezhima) keeps acceptable temperatures for all components of the Zvezda Service Module, SM, including habitable volume, as well as those systems operating in the vacuum of space beyond the pressurized compartments.


Exterior view of the Zvezda Service Module.



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This page is maintained by Anatoly Zak;

Last update: September 16, 2022


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Cutaway view of the Zvezda Service Module. Credit: TsUP TsNIIMash


The Electron oxygen-generating unit is a part of Zvezda's life-support system (Insider Content). Credit: NASA


Flight control computers onboard the service module of the ISS. Credit: NASA


Artist rendering of Expose-R experiment, which was removed by spacewalking cosmonauts on Jan. 21, 2011. Credit: NASA

ATV approach

The ATV-2 cargo ship approaches the service module on the International Space Station in February 2011. Credit: Roskosmos



A TORU post inside the Service Module. Credit: Roskosmos


A wide-angle view inside the transfer compartment of the Service Module during Expedition 31 on May 12, 2012. Credit: NASA


Location of docking reflectors on the aft port of the Zvezda Service Module. Credit: NASA


Interior view of the main window aboard the service module during the flight circa 2017. Credit: ESA


View at the active probe of the Pirs Docking Compartment, SO1, in the interior of the Transfer Compartment, PKhO, of the Zvezda Service Module on July 9, 2021. Click to enlarge. Credit: Roskosmos