Editing Soyuz (spacecraft) (section)

== Design ==
[[File:Soyuz-TMA parts.jpg|thumb|Exploded-view drawing of the modules of the Soyuz spacecraft]][[File:Spaceships.svg|thumb|Currently operational crewed spacecraft (at least orbital class)]]

Soyuz spacecraft are composed of three primary sections (from top to bottom, when standing on the launch pad):

* [[Orbital module]]: A [[spheroid]] compartment providing living space for the crew.
* [[Descent module]]: A small, aerodynamic capsule where the crew is seated for launch and return the crew to Earth.
* [[Service module]]: A cylindrical section housing propulsion, power, and other systems.

The orbital and service modules are discarded and destroyed upon [[Atmospheric entry|reentry]]. This design choice, while seemingly wasteful, reduces the spacecraft's weight by minimizing the amount of heat shielding required. As a result, Soyuz offers more habitable interior space ({{Convert|7.5|m3|disp=comma|abbr=off}}) compared to its [[Apollo command and service module|Apollo counterpart]] ({{Convert|6.3|m3|disp=comma|abbr=on}}).  While the reentry module does return to Earth, it is not reusable, a new Soyuz spacecraft must be made for every mission.<ref>{{cite web |title=The Russian Soyuz spacecraft |url=http://www.esa.int/Enabling_Support/Space_Transportation/Launch_vehicles/The_Russian_Soyuz_spacecraft}}</ref>

Soyuz can carry up to three crew members and provide life support for about 30&nbsp;[[person-day]]s.{{Citation needed|reason=What is the source for this number?|date=January 2025}}

A payload fairing protects Soyuz during launch and is jettisoned early in flight. Equipped with an automated docking system, the spacecraft can operate autonomously or under manual control.

=== Launch escape system ===
The [[Vostok (spacecraft)|Vostok]] spacecraft used an [[ejector seat]] to bail out the cosmonaut in the event of a low-altitude launch failure, as well as during reentry; however, it would probably have been ineffective in the first 20&nbsp;seconds after liftoff, when the altitude would be too low for the parachute to deploy. Inspired by the [[Project Mercury|Mercury]] LES,{{Citation needed|date=May 2022}} Soviet designers began work on a similar system in 1962. This included developing a complex sensing system to monitor various launch-vehicle parameters and trigger an abort if a booster malfunction occurred. Based on data from [[R-7 (rocket family)|R-7]] launches over the years, engineers developed a list of the most likely failure modes for the vehicle and could narrow down abort conditions to premature separation of a strap-on booster, low engine thrust, loss of combustion-chamber pressure, or loss of booster guidance. The spacecraft abort system (SAS; {{langx|ru|Система Аварийного Спасения|translit=Sistema Avarijnogo Spaseniya}}) could also be manually activated from the ground, but unlike American spacecraft, there was no way for the cosmonauts to trigger it themselves.

Since it turned out to be almost impossible to separate the entire payload shroud from the Soyuz service module cleanly, the decision was made to have the shroud split between the service module and descent module during an abort. Four folding stabilizers were added to improve aerodynamic stability during ascent. Two test runs of the SAS were carried out in 1966–1967.<ref name="Shayler2009">{{cite book |url=https://books.google.com/books?id=wEHL8MIhRa8C&pg=PA158 |title=Space Rescue: Ensuring the Safety of Manned Spacecraft |publisher=Springer Science + Business Media |series=Springer-Praxis Books in Space Exploration |first=David J. |last=Shayler |pages=153–160 |date=2009 |isbn=978-0-387-69905-9}}</ref>

[[File:Jsc2006e11326.jpg|thumb|right|alt=Upper section of Soyuz TMA-8 during assembly|The capsule and [[Soyuz abort modes|escape system]] of the Soyuz TMA-8 mission during assembly]]The basic design of the SAS has remained almost unchanged in 50&nbsp;years of use, and all Soyuz launches carry it. The only modification was in 1972, when the aerodynamic fairing over the SAS motor nozzles was removed for weight-saving reasons, as the redesigned Soyuz 7K-T spacecraft carried extra life-support equipment. The uncrewed [[Progress (spacecraft)|Progress]] resupply ferry has a dummy escape tower and removes the stabilizer fins from the payload shroud. There have been three failed launches of a crewed Soyuz vehicle: [[Soyuz 7K-T No.39|Soyuz 18a]] in 1975, [[Soyuz 7K-ST No. 16L|Soyuz T-10a]] in 1983 and [[Soyuz MS-10]] in October 2018. The 1975 failure was aborted after escape-tower jettison. In 1983, Soyuz T-10a's SAS successfully rescued the cosmonauts from an on-pad fire and explosion of the launch vehicle.<ref>{{cite web |url=http://www.russianspaceweb.com/soyuz_sas.html |title=Emergency escape rocket: The ultimate lifeboat for spacecraft |publisher=RussianSpaceWeb |first=Anatoly |last=Zak}}</ref> Most recently, in 2018, the SAS sub-system in the payload shroud of Soyuz MS-10 successfully rescued the cosmonauts from a rocket failure 2&nbsp;minutes and 45&nbsp;seconds after liftoff, after the escape tower had already been jettisoned.

=== Orbital module ===
[[File:Soyuz orbital module.jpg|thumb|Drawing highlighting the orbital module]]
{{Main|Orbital module}}

The forepart of the spacecraft is the orbital module ({{langx|ru|бытовой отсек|links=no|translit=bytovoi otsek}}), also known as habitation section. It houses all the equipment that will not be needed for reentry, such as experiments, cameras or cargo. The module also contains a toilet, docking avionics and communications gear. Internal volume is {{cvt|6|m3}}, living space is {{cvt|5|m3}}. On later Soyuz versions (since Soyuz&nbsp;TM), a small window was introduced, providing the crew with a forward view.

A hatch between it and the descent module can be closed so as to isolate it to act as an airlock if needed so that crew members could also exit through its side port (near the descent module). On the launch pad, the crew enter the spacecraft through this port. This separation also lets the orbital module be customized to the mission with less risk to the life-critical descent module. The convention of orientation in a [[micro-g environment]] differs from that of the descent module, as crew members stand or sit with their heads to the docking port. Also the rescue of the crew whilst on the launch pad or with the SAS system is complicated because of the orbital module.

Separation of the orbital module is critical for a safe landing; without separation of the orbital module, it is not possible for the crew to survive landing in the descent module. This is because the orbital module would interfere with proper deployment of the descent module's parachutes, and the extra mass exceeds the capability of the main parachute and braking engines to provide a safe soft-landing speed. In view of this, the orbital module was separated before the ignition of the return engine until the late 1980s. This guaranteed that the descent module and orbital module would be separated before the descent module was placed in a reentry trajectory. However, after the problematic landing of [[Soyuz&nbsp;TM-5]] in September 1988 this procedure was changed, and the orbital module is now separated after the return maneuver. This change was made as the TM-5 crew could not deorbit for 24&nbsp;hours after they jettisoned their orbital module, which contained their sanitation facilities and the docking collar needed to attach to ''[[Mir]]''. The risk of not being able to separate the orbital module is effectively judged to be less than the risk of needing the facilities in it, including the toilet, following a failed deorbit.

=== Descent module ===
[[File:Soyuz descent module.jpg|thumb|Drawing highlighting the descent module]]
[[File:Replica of the Soyuz spacecraft's Entry Module.jpg|thumb|Replica of the Soyuz spacecraft's reentry module at the [[Euro Space Center]] in [[Belgium]]]]

The [[descent module]] ({{langx|ru|Спуска́емый Аппара́т|spuskáyemy apparát}}), also known as a reentry capsule, is used for launch and the journey back to Earth. Half of the descent module is covered by a heat-resistant covering to protect it during [[Atmospheric entry|reentry]]; this half faces forward during reentry. It is slowed initially by the atmosphere, then by a braking parachute, followed by the main parachute, which slows the craft for landing. At one meter above the ground, solid-fuel braking engines mounted behind the [[heat shield]] are fired to give a soft landing. One of the design requirements for the descent module was for it to have the highest possible volumetric efficiency (internal volume divided by hull area). The best shape for this is a sphere&nbsp;– as the pioneering [[Vostok (spacecraft)#Design|Vostok]] spacecraft's descent module used&nbsp;– but such a shape can provide no lift, resulting in a purely [[Atmospheric entry|ballistic reentry]]. Ballistic reentries are hard on the occupants due to high deceleration and cannot be steered beyond their initial deorbit burn. Thus it was decided to go with the "headlight" shape that the Soyuz uses&nbsp;– a hemispherical upper area joined by a barely angled (seven degrees) conical section to a classic spherical section heat shield. This shape allows a small amount of lift to be generated due to the unequal weight distribution. The nickname was thought up at a time when nearly every headlight was circular. The small dimensions of the descent module led to it having only two-man crews after the death of the [[Soyuz&nbsp;11]] crew. The later [[Soyuz-T]] spacecraft solved this issue. Internal volume of Soyuz&nbsp;SA is {{cvt|4|m3}}; {{cvt|2.5|m3}} is usable for crew (living space).

The thermal protection system on the slightly conical side walls is stood off from the structure to also provide micrometeoroid protection in orbit.<ref name=Soyuz-TPS>[https://ntrs.nasa.gov/citations/20130013840 ''International Space Station (ISS) Soyuz Vehicle Descent Module Evaluation of Thermal Protection System (TPS) Penetration Characteristics'']</ref>
The slightly curved heat shield on the bottom consists of "21mm to 28mm thick ablator (glass-phenolic composite) which
is held by brackets approximately 15mm from the 3.5mm thick aluminum AMg-6 substrate. VIM low-density silica fibrous insulation (8mm thick) is contained in the gap between the heat shield ablator and aluminum substrate."<ref name=Soyuz-TPS/>

=== Service module ===
[[File:Soyuz propulsion module.jpg|thumb|Drawing highlighting the instrumentation/propulsion module]]
At the back of the vehicle is the [[service module]] ({{langx|ru|прибо́рно-агрега́тный отсе́к|pribórno-agregátny otsék}}). It has a pressurized container shaped like a bulging can (instrumentation compartment, {{Transliteration|ru|priborniy otsek}}) that contains systems for temperature control, electric power supply, long-range [[Radio|radio communications]], [[Telemetry|radio telemetry]], and instruments for orientation and control. A non-pressurized part of the service module (propulsion compartment, {{Transliteration|ru|agregatniy otsek}}) contains the main engine and a liquid-fuelled [[Spacecraft propulsion|propulsion system]], using [[Dinitrogen tetroxide|N<sub>2</sub>O<sub>4</sub>]] and [[Unsymmetrical dimethylhydrazine|UDMH]],<ref>{{Cite web |title=KTDU-80 |url=http://www.astronautix.com/k/ktdu-80.html |access-date=2022-10-21 |website=www.astronautix.com}}</ref> for maneuvering in orbit and initiating the descent back to [[Earth]]. The ship also has a system of low-thrust engines for orientation, attached to the intermediate compartment ({{Transliteration|ru|perekhodnoi otsek}}). Outside the service module are the sensors for the orientation system and the solar array, which is oriented towards the [[Sun]] by rotating the ship. An incomplete separation between the service and reentry modules led to emergency situations during [[Soyuz&nbsp;5]], [[Soyuz&nbsp;TMA-10]] and [[Soyuz&nbsp;TMA-11]], which led to an incorrect reentry orientation (crew ingress hatch first). The failure of several explosive bolts did not cut the connection between the service and reentry modules on the latter two flights.

=== Reentry procedure ===
The Soyuz uses a method similar to the 1970s-era [[United States]] [[Apollo command and service module]] to deorbit itself. The spacecraft is turned engine-forward, and the main engine is fired for deorbiting on the far side of Earth ahead of its planned landing site. This requires the least propellant for [[Atmospheric entry|reentry]]; the spacecraft travels on an elliptical [[Hohmann transfer orbit]] to the entry interface point, where atmospheric drag slows it enough to fall out of orbit.

Early Soyuz spacecraft would then have the service and orbital modules detach simultaneously from the descent module. As they are connected by tubing and electrical cables to the descent module, this would aid in their separation and avoid having the descent module alter its orientation.{{Citation needed|date=October 2018}} Later Soyuz spacecraft detached the orbital module before firing the main engine, which saved propellant. Since the [[Soyuz&nbsp;TM-5]] landing issue, the orbital module is once again detached only after the reentry firing, which led to (but did not cause) {{Citation needed|date=July 2024}}emergency situations of [[Soyuz&nbsp;TMA-10]] and [[Soyuz TMA-11|TMA-11]]. The orbital module cannot remain in orbit as an addition to a space station, as the airlock hatch between the orbital and reentry modules is a part of the reentry module, and the orbital module therefore depressurizes after separation.

Reentry firing is usually done on the "dawn" side of the Earth, so that the spacecraft can be seen by recovery helicopters as it descends in the evening twilight, illuminated by the Sun when it is above the shadow of the Earth.{{Citation needed|date=October 2018}} The Soyuz craft is designed to come down on land, usually somewhere in the deserts of Kazakhstan in Central Asia. This is in contrast to the early United States crewed spacecraft and the current SpaceX Crew Dragon, which splash down in the ocean.

=== Spacecraft systems ===
[[File:Soyuz Diagram.svg|thumb|290px|Thermal and life support systems diagram]]
* '''Thermal control system''' – {{Transliteration|ru|sistema obespecheniya teplovogo rezhima, SOTR}}
* '''Life support system''' – {{Transliteration|ru|kompleks sistem obespecheniya zhiznedeyatelnosti, KSOZh}}
* '''Power supply system''' – {{Transliteration|ru|sistema elektropitaniya, SEP}}
* '''Communication and tracking systems''' – Rassvet (Dawn) radio communications system, onboard measurement system (SBI), Kvant-V spacecraft control, Klyost-M television system, orbit radio tracking (RKO)
* '''Onboard complex control system''' – {{Transliteration|ru|sistema upravleniya bortovym kompleksom, SUBK}}
* '''Combined propulsion system''' – {{Transliteration|ru|kompleksnaya dvigatelnaya ustanovka, KDU}}
* '''Chaika-3 motion control system (SUD)'''
* '''Optical/visual devices (OVP)''' – VSK-4 ({{Transliteration|ru|vizir spetsialniy kosmicheskiy-4}}), night vision device (VNUK-K, {{Transliteration|ru|visir nochnogo upravleniya po kursu}}), docking light, pilot's sight (VP-1, {{Transliteration|ru|vizir pilota-1}}), laser rangefinder (LPR-1, {{Transliteration|ru|lazerniy dalnomer-1}})
* '''[[Kurs (docking navigation system)|Kurs rendezvous system]]'''
* '''[[SSVP docking system]]'''
* '''[[TORU]] control mode'''
* '''Entry actuators system''' – {{Transliteration|ru|sistema ispolnitelnikh organov spuska, SIO-S}}
* '''Landing aids kit''' – {{Transliteration|ru|kompleks sredstv prizemleniya, KSP}}
* '''Portable survival kit''' – {{Transliteration|ru|nosimiy avariyniy zapas, NAZ}}, containing a [[TP-82]] or [[Makarov pistol]]
* '''[[Launch escape system]]''' – {{Transliteration|ru|sistema avariynogo spaseniya, SAS}}

[[File:Drawing-Soyuz-TMA-exp12.png|600px|center]]
{{col-begin|width=100%}}
{{col-3}}
;'''Orbital module (A)'''
:'''1''' SSVP docking mechanism
:'''2''', '''4''' Kurs rendezvous radar antenna
:'''3''' television transmission antenna
:'''5''' camera
:'''6''' hatch
{{col-3}}
;'''Descent module (B)''':
:'''7''' parachute compartment
:'''8''' periscope
:'''9''' porthole
:'''11''' heat shield
{{col-3}}
;'''Service module (C)''':
:'''10''', '''18''' attitude control engines
:'''12''' Earth sensors
:'''13''' Sun sensor
:'''14''' solar panel attachment point
:'''15''' thermal sensor
:'''16''' Kurs antenna
:'''17''' main propulsion
:'''19''' communication antenna
:'''20''' fuel tanks
:'''21''' oxygen tank
{{col-end}}