Service module
A service module is a spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

 compartment containing a variety of support systems used for spacecraft operations. Usually located in the uninhabited area of the spacecraft, the service module is jettisoned upon the completion of the mission, and usually burns up during atmospheric reentry
Atmospheric reentry
Atmospheric entry is the movement of human-made or natural objects as they enter the atmosphere of a celestial body from outer space—in the case of Earth from an altitude above the Kármán Line,...

. The service module is the equivalent to the spacecraft bus assembly on unmanned spacecraft.


Depending upon the spacecraft architecture and system design, a typical service module will usually contain the following:
  • Fuel cell
    Fuel cell
    A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used...

    s, solar panels
    Solar cell
    A solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....

    , or batteries
    Battery (electricity)
    An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

     to provide electrical power to the spacecraft (batteries are also used in the crew capsule)
  • Liquid hydrogen
    Liquid hydrogen
    Liquid hydrogen is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.To exist as a liquid, H2 must be pressurized above and cooled below hydrogen's Critical point. However, for hydrogen to be in a full liquid state without boiling off, it needs to be...

     (LH2) and liquid oxygen
    Liquid oxygen
    Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...

     (LOX) for fuel cell operation and water production, with LOX also being used to provide breathing oxygen for the crew.
  • Pressurized helium
    Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

     or nitrogen
    Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

     to force consumables and fuel from source tanks to their destinations.
  • Guidance computer systems and related sensors
  • Fuel and oxidizer for reaction control
    Reaction control system
    A reaction control system is a subsystem of a spacecraft whose purpose is attitude control and steering by the use of thrusters. An RCS system is capable of providing small amounts of thrust in any desired direction or combination of directions. An RCS is also capable of providing torque to allow...

     and propulsion
    Spacecraft propulsion
    Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the...

  • Thermal control systems for proper heating and cooling of above systems.

While this would be used for a "baseline" service module, a service module may also be modified for additional functions. An example would be the equipment module on Gemini IX-A, when it was modified to carry the U.S. Air Force-developed Astronaut Maneuvering Unit
Manned Maneuvering Unit
The Manned Maneuvering Unit is an astronaut propulsion unit which was used by NASA on three space shuttle missions in 1984. The MMU allowed the astronauts to perform untethered EVA spacewalks at a distance from the shuttle. The MMU was used in practice to retrieve a pair of faulty communications...

 that would have been tested by astronaut Eugene Cernan, but was cancelled when his spacesuit overheated, causing his visor to fog up. But the best example would be the final three Apollo missions, in which the J-series service modules included scientific instrument module (SIM) bays that took pictures and other readouts in lunar orbit. In addition to the film cameras, similar to those used on the Lunar Orbiter spacecraft and requiring the Command Module Pilot to perform a deep-space EVA during the return trip, two of the SIM bays, on Apollos 15
Apollo 15
Apollo 15 was the ninth manned mission in the American Apollo space program, the fourth to land on the Moon and the eighth successful manned mission. It was the first of what were termed "J missions", long duration stays on the Moon with a greater focus on science than had been possible on previous...

 and 16
Apollo 16
Young and Duke served as the backup crew for Apollo 13; Mattingly was slated to be the Apollo 13 command module pilot until being pulled from the mission due to his exposure to rubella through Duke.-Backup crew:...

, also launched a lunar "subsatellite" before the astronauts performed the Trans-Earth Injection burn with the onboard service propulsion system.

Russian variation

The Russian phrase for service module for the Soyuz spacecraft
Soyuz spacecraft
Soyuz , Union) is a series of spacecraft initially designed for the Soviet space programme by the Korolyov Design Bureau in the 1960s, and still in service today...

 is sometimes more directly translated "Instrument-Assembly Compartment." This comes from the design feature of having the guidance and other computer systems in a separate pressure chamber (the instruments) from the rocket engines, their propellant tanks, and the life support tanks (from the German Aggregat, which gets translated "assembly"). The Russians do not use the word "module" for their own spacecraft, though it is in the Russian language.

Retired spacecraft

Vostok equipment module
Vostok spacecraft
The Vostok was a type of spacecraft built by the Soviet Union. The first human spaceflight in history was accomplished on this spacecraft on April 12, 1961, by Soviet cosmonaut Yuri Gagarin....

 Voskhod equipment module
Voskhod spacecraft
The Voskhod was a spacecraft built by the Soviet Union's space program for human spaceflight as part of the Voskhod programme. It was a development of and a follow-on to the Vostok spacecraft...

 Gemini equipment module
Project Gemini
Project Gemini was the second human spaceflight program of NASA, the civilian space agency of the United States government. Project Gemini was conducted between projects Mercury and Apollo, with ten manned flights occurring in 1965 and 1966....

 Apollo service module Apollo lunar module descent stage
Apollo Lunar Module
The Apollo Lunar Module was the lander portion of the Apollo spacecraft built for the US Apollo program by Grumman to carry a crew of two from lunar orbit to the surface and back...

Proposed, cancelled, or in development

Orion service module (In development) Crewed ATV service module
Automated Transfer Vehicle
The Automated Transfer Vehicle or ATV is an expendable, unmanned resupply spacecraft developed by the European Space Agency . ATVs are designed to supply the International Space Station with propellant, water, air, payload and experiments...

 (Proposed)  CSTS service module
CSTS or ACTS is a human spaceflight system proposal. It was originally a joint project between the European Space Agency and the Russian Space Agency , but is now solely an ESA project...

 (Cancelled) Kliper service module
Kliper is a partly reusable manned spacecraft, proposed by RSC Energia.Designed primarily to replace the Soyuz spacecraft, Kliper has been proposed in two versions: as a pure lifting body design and as spaceplane with small wings...

 (Cancelled)  Hermes resource module
Hermes (shuttle)
Hermes was a proposed spaceplane designed by the French Centre National d'Études Spatiales in 1975, and later by the European Space Agency. It was superficially similar to the US X-20. France proposed in January 1985 to go through with Hermes development under the auspices of the ESA. Hermes was...


See also

  • Orbital module
    Orbital module
    The orbital module is a portion of spacecraft used only in orbit. These have developed from the Soviet Soyuz spacecraft.-Soyuz orbit module:The orbit module is a spherical part of Soviet-Russian Soyuz space ship series...

  • Reentry capsule
    Reentry capsule
    A reentry capsule is the portion of a spacecraft which returns to Earth following a space flight. The shape is determined partly by aerodynamics; a capsule is aerodynamically stable falling blunt end first, which allows only the blunt end to require a heat shield for atmospheric reentry. Its shape...

  • Command module
  • Space capsule
    Space capsule
    A space capsule is an often manned spacecraft which has a simple shape for the main section, without any wings or other features to create lift during atmospheric reentry....

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