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Service Module Zvezda

Zarya computer illustration (ESA) Zvezda («Звезда», “Star”) is the core of the ISS, providing living quarters and life support for the crew. It was originally intended for the Mir-2 space station and the design was based on the Mir Core Module, but when this was cancelled after the fall of the Soviet Union, it was amalgamated into the ISS instead.

Zvezda is the first entirely Russian module (i.e. built and funded by Russia). The main developer was RKK Energiya and main subcontractor was GKNPTs Khrunichev. It was launched on a Proton-K rocket on 12 July 2000.

Zvezda is the most complex structure as it has many tasks to support: crew and ground communications, life support, Station orientation, enabling the approach and docking of Russian Progress and Soyuz ships, supporting experiments and spacewalks.

Full name:

СМ: Служебный Модуль
SM: Service Module
Sluzhebnyi Modul’


Zvezda is a cylinder comprising four sections.


PKhO transfer compartment (ПхО, Переходный Отсек – PKhO, Perekhodniy Otsek): This spherical compartment provides 3 docking ports (it could be built with 5) and also serves as a back-up airlock if no specialized airlock is attached as it can be depressurized. It is the transfer point between the SM and the other ISS modules. It is 2.78 m in length with a volume of 6.85 m³. There are four lights inside. It has one axial (facing forward) and two lateral (top and bottom) hybrid passive docking ports of the type SSVP-M G8000, ССВП-М Г8000. Zarya is permanently docked to the axial port. The top port was to have supported the Science & Power Platform (НЭП, NEP), but with the cancellation of this, Pirs will eventually be moved there instead. Pirs is currently docked to the bottom (Earth-facing) port.

The Progress and Soyuz ships can’t dock to any PKhO ports as they have a different docking mechanism (probe-and-drogue). The PKhO ports are for modules only.

Working compartment section (РО, Рабочий Отсек – RO, Rabochii Otsek): This is the largest part of the SM and contains life support systems, instruments and crew quarters. It is 7.7 meters in length and has a total of 14 windows. It comprises two cylinders joined together by a conical adapter:

  • Instrument Compartment (ПО, Приборой Отсек – PO, Priboroi Otsek): the smaller section aft of the PKhO contains the Station command post (central computer) and related equipment. It is 3.5 m in length and 2.9 m in diameter with a volume of 75.0 m³.
  • Habitable Compartment (ЖО, Жилой Отсек – ZhO, Zhloi Otsek): behind the PO, in the larger cylinder, contains crew life support and two cabins (kayuti, каюты). The kayuti each has a measurement of 0.73 × 0.85 × 1.89 m (2.4 × 2.8 × 6.2 ft). There is a small washroom and sanitary compartment with a toilet (volume of 1.2 m³). Food is prepared at a galley table and an exercise treadmill lies in the center. It contains the life support equipment such as the Vozdukh CO2 filter and the Elektron oxygen generator (which proved to be rather noisy for the crew). The ZhO is 2.9 m in length and 4.1 m in diameter with a volume of 35.1 m³.

The intermediate chamber (ПК, Промежуточная Камера – PK, Promezhutochnaya Kamera): This is the transfer point between the RO and a docked Soyuz or Progress spacecraft. It is 2.0 m in diameter and 2.34 m in length. The internal volume is 7.0 m³. At the aft end is the passive docking assembly SSVP G4000, ССВП Г4000 (probe-and-cone type). The port can accommodate Soyuz and Progress dockings, and the European Automated Transfer Vehicle. A TV camera is attached to the outside to enable visual display of dockings.

The assembly compartment (АО, Агрегатный Отсек – AO, Agretatnyi Otsek): This is wrapped around the PK at the aft end and is unpressurized. It is used to position the orientation and propulsion engines around the module. There are also various antennae mounted for communications.

Docking ports summary

  • Forward docking port: АСР-ГО, ASP-GO (Passive docking assembly – hybrid axial)
  • Nadir/bottom port: АСП-ГБ1, ASP-GB1 (Passive docking assembly – hybrid lateral)
  • Zenith/top port: АСП-ГБ2, ASP-GB2
  • Aft port: АСП-О, ASP-O


The onboard control complex (БКУ, Бортовой Комплекс Управления – BKU, Bortovoi Kompleks Upravleniya) that oversees the operation of the Russian ISS modules comprises the following systems:

  • Motion control system. Monitors ISS attitude control via jet engines and gyroscopes. Navigates via satellites and corrects the orbit of the ISS. Conducts docking and undocking operations with spacecraft.
  • The onboard computer system (БВС, Бортовая Вычислительная Система – BVS, Bortovaya Vychislitel’naya Sistema) is the foundation of the BKU and is the “brains” of the module, enabling the crew to control its systems and those of the other Russian modules, and interface with the U.S. segment. The European-Russian designed Data Management System is the processing center for data.
  • The onboard radio complex (БРК, Бортовой Радиокомплекс – BRK, Bortovoi Radiokompleks). It enables two-way communications between the RS and Moscow Mission Control (TsUP). There are 5 systems: Regul (radio – РСУС, RSUS); television (ТВС, TVS); internal telephone-telegraph communications (STTS, СТТС); the orbit radio control system (РКО, RKO); and the Lira radio-technical system (БРТС, BRTS).
  • The onboard measurement system (СБИ, Система Бортовых Измерений – SBI, Sistema Bortovykh Izmerenii) is a telemetry system that transmits data to TsUP concerning the status and health of the modules and crew.
  • the control system of onboard equipment (СУБК, SUBK) diagnoses the status of the SM onboard systems.
  • the teleoperator mode control equipment (TORU) of approaching and docking automatic cargo spacecraft (i.e. Progress). This is a manual back-up docking system (controlled by a crewperson) in case the automatic Kurs docking system fails.

The electrical power supply system (СЕП, SEP) supplies power to Zvezda, and can also transfer power from the U.S. segment if needed. Solar power is gathered by two solar arrays (СБ, SB) of 38 m² each. They can be oriented toward the sun either automatically or manually by the crew. Power is stored in 8 800A storage batteries (АБ, AB).

The united engine installation (ОДУ, ODU) controls and stabilizes the ISS. There are 2 two main corrective engines (КД KD) and 32 smaller engines (ДО, DO) 11D428A for precision orientation. The oxidizer used is nitric tetraoxide and propellant is nitrogen. The tanks these are stored in are replenished by Progress cargo ships. The module has 4 tanks (2 for fuel, 2 for oxidizer), which can contain up to 860 kilograms of propellant in total.

The thermal control system (COTP, SOTR) maintains the temperature inside the modules and regulates air ventilation. It is separate from the other systems and works constantly. Temperature in the crew compartments is maintained in the 18°C to 28°C range.

The life support system (СОЖ, SOZH) provides extensive equipment to remove CO2 and other impurities via the Vozdukh, provide oxygen via the Elektron generator or solid cannisters and generally maintain an appropriate atmospheric composition (СОГС, SOGS) for humans. Water provision (СВО, SVO) is enabled through a condensate regeneration system and is also brought up from Earth and stored in tanks. A toilet and washroom facilities support crew hygiene needs (SSGO). There are, of course, food supplies onboard (СПО, SPO). There is also a fire detection system and extinguishers. Medical supplies are also provided.

Data tables

Zvezda: fundamental technical characteristics
Maximum crew the module can support to 6
Mass in orbit, kg 20,295
Length of housing, mm 13,110
Maximum diameter, mm 4350
Volume of airtight sections, cubic meters 89
Spread of solar batteries, mm 29,730
Area of photovoltaic cells, meters squared 76
Average power of power supply, KVT/SUT 9.8
Fuel mass, kg 860
Duration of functioning in orbit, years 15
Manufacturer Khrunichev
Zvezda launch data
Designation 17KSM №12801
NASA designation 1R
Launch vehicle Proton-K (№398-01)
Launch site Launch complex 81/23, Baikonur Cosmodrome, Republic of Kazakhstan
Launch date 12 July 2000 at 04:56:36
Docking date 26 July 2000 at 00:45 to Zarya aft port
Mission Launch of Zvezda Service Module (docked with Zarya). Third ISS module to be launched (after Zarya then Unity)


Zvezda windows

Zvezda has 14 windows, most downward-facing. There is one window in each kayuta, каюта (№s 1 – port, and 2 – starboard – not shown here), and 6 set into the floor of the Working Compartment (№s. 3-8), plus one 40 cm-diameter Observation Window (№ 9) set into the flared skirting between the Working and Living Compartments. There are 3 22.8 cm windows in the Forward Transfer Compartment for viewing docking activities, and one set into the rear docking port. Window 7 has a shade; window 4 a vertical sight. (Diagram from the PDF documents linked to below.)

External links to three Zvezda exterior diagrams at Spaceref.com (PDF documents – to save without opening the document, right-click on the link and select “Save Target As”):

The following Zvezda exterior diagrams are taken from the Space Station User’s Guide: NASA ISS EVA Operations Documents PDFs at Spaceref.com:

Boeing diagram: Zvezda Service Module: Early Crew Living Quarters.

Zvezda in orbit
Nadir view of Zvezda in orbit, 2 December 2000.
Aleksandr Kaleri eating a meal at the Galley table
This view shows an aft view of the Service Module; starboard is to the left, port to right and the hatch leading to the docked Progress cargo ship is behind Aleksandr Kaleri (ISS-8), who is at the Galley table. To his right is one of the twin kayuti, каюты (cabins – singular: kayuta, каюта). Photos of Yurii Gagarin and Konstantin Tsiolkovskii are attached to the panel above the rear hatch.
Interior view of Zvezda, looking forward
A view looking forward (toward Zarya), showing the Central Workstation with its four laptops.