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Descent module, SA

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Interior

Above: Inside the early version of the habitation module onboard the Soyuz spacecraft. The docking port is at the top, the transfer hatch into the descent module is at the bottom of the photo. The main equipment section nick-named "servant" (cupboard) is on the left and the smaller section known as "divan" (coach) is on the right.


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The spherical habitation module, BO, was originally designed to provide extra convenience for the crew during missions, which could last as long as a week. The habitation module allowed to minimize the size and mass of the crew module, SA, which had to be covered with heavy thermal protection layers to protect it during the fiery descent in the Earth atmosphere. The thin-walled habitation module essentially offered the crew a second room for both work and rest. In addition, by merely being a forward docking section of the spacecraft, the habitation module provided additional safe clearance for the crew during rendezvous with other spacecraft, such as lunar modules or space stations. When docked to another spacecraft, the habitation module would serve as a hallway for crew transfer. (52)

In most cases, but not always, the docking hardware and the rendezvous antennas would be located in the front of the habitation module. Beginning with the mission of Soyuz-10, the habitation module was equipped with the docking and internal transfer system known by the Russian abbreviation SSVP - Sistema Stykovki i Vnutrennego Perekhoda. (429) SSVP-type docking ports have a hatch, enabling transfer between spacecraft in a short-sleeve environment.

The opposite end of the habitation module is always connected to the reentry capsule with a transfer hatch. Finally, a third hatch on the side of the habitation module, enables this compartment to serve as an airlock, in case the crew needs to get outside the spacecraft in orbit for a spacewalk (Extra-Vehicular Activity, EVA). In such cases, spacewalking cosmonauts dressed in spacesuits can let the air out of the habitation module, while still keeping the reentry capsule of the Soyuz pressurized. Spacewalks from the habitation module are still possible, when the Soyuz is docked to another spacecraft. The only condition is closing the docking port hatch between the Soyuz and the vehicle it is docked to. The same EVA hatch also serves as entry point for the crew members, when they board the ship on the launch pad.

A majority of the internal hardware of the habitation module is grouped into two sections located on both sides of the module, thus leaving the middle of the compartment as a free space for the crew. These sections became known in Russian jargon as "divan" (coach) and "servant" (cupboard) after two most common furniture pieces in Soviet-era living rooms.

The habitation module also contains a toilet, docking avionics and communications gear. In several "solo" missions in the 1970s, (not involving rendezvous with other spacecraft), the docking hardware in the habitation module was replaced with custom-built payload sections.

Structurally, the habitation module is made of two semispherical magnesium sections with a 0.3-meter cylindrical segment between them. Originally, the section had two windows. During the evolution of the spacecraft, a special blister was introduced, providing a forward view in the course of rendezvous and docking.

Originally, the habitation module was designed to separate from the descent module, SA, prior to the reentry maneuver at the end of a mission. However in the wake of a nearly disastrous incident in 1988, the habitation module would only be jettisoned after the braking maneuver, despite the extra propellant required to push the whole spacecraft off the orbit. Otherwise, any major failure of the braking system would strand the crew inside the cramped descent module with no access to toilet and other critical life-support systems.

During the return trip of the Soyuz spacecraft from the station, bags of trash are routinely loaded into the habitation module to be disposed of along with it. The habitation module burns up during reentry into the atmosphere, as does the instrument module, PAO.


APPENDIX

Known specifications of the habitation module (Soyuz TM version):

Mass
1,200-1,300 kilograms (2, 429)
Length 2.6 meters (3,44 meters with docking port)
Diameter 2.2 meters
The total volume of the BO module 6.5-6.6 cubic meters (2, 429)
Free internal volume 4 cubic meters (2)
Transfer hatch diameter 800 millimeters
Entrance/EVA hatch diameter 640 millimeters (2)

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Page author: Anatoly Zak; Last update: April 1, 2011

Page editor: Alain Chabot; Last edit: March 18, 2011

Copyright © 2011 RussianSpaceWeb.com

PICTURE GALLERY

BO

Interior

A habitation module of an early version of the Soyuz spacecraft and its interior as viewed through the entrance hatch. Copyright © 2011 Anatoly Zak


BO

Technician assembles hardware inside the habitation module of the Soyuz spacecraft circa 1970. Click to enlarge. Credit: 152


BO

A habitation module of the second-generation Soyuz. Note smaller docking assembly, which enables an internal transfer of the crew. Copyright © 2011 Anatoly Zak


The processing crew install protective ring on the docking port of the Soyuz TMA-4 spacecraft. A blister with the front view window on the habitation module is clearly visible at the top. Credit: RKK Energia


BO

A rare photo showing interface of the habitation module with the descent capsule on the Soyuz spacecraft. Credit: RKK Energia


Cargo

Paolo Nespoli, a member of Soyuz TMA-20 crew, poses in front of the numerous cargo bags routinely traveling to the space station inside the habitation module. Credit: Roskosmos

Servant

Catherine Coleman, a member of Soyuz TMA-20 crew, opens the storage area known as "servant" inside the habitation module. Credit: Roskosmos


Cover

A transfer tunnel into the descent capsule, viewed from the habitation module. A special folding cover (right) is designed to prevent trash and other objects from falling out from the depressurized habitation module after its separation from the descent capsule at the very end of the mission. Credit: Roskosmos


BO

An interior of the habitation module onboard Soyuz TMA spacecraft looking toward the blister (left). Credit: NASA


BO

A look inside of the habitation module of the Soyuz TMA spacecraft from the side of the docking hatch. Credit: NASA


Toilet

An orbital toilet system. Copyright © 2010 Anatoly Zak