The orbital module is a portion of spacecraft used only in orbit. It is separated from the manned reentry capsule before reentry. The orbital module provides 'habitat' space to use in orbit, while the reentry capsule tends to be focused on the machinery needed to get seated passengers back safely, with heavy structural margins. These have developed from the Soviet Soyuz spacecraft.
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Soyuz orbit module
The orbit module is a spherical part of Soviet-Russian Soyuz space ship series. Designed for use only in orbit, the module does not need to be strengthened to survive re-entry, allowing it to provide more usable space for less weight than other manned capsule designs.
It serves mainly for rest and hygiene procedures of a ship's crew during phase of orbital flight when used as a space station ferry, though on early Soyuz missions the module was used for experiments and even as an airlock for the Soyuz 4/Soyuz 5 EVA crew transfer.
Shenzhou orbit module
In the Chinese Shenzhou spacecraft, the orbital module has been upgraded to carry its own solar panels and orbital maneuver system, so it is capable of operating independently as an unmanned free-flying spacecraft after separating from the reentry module and the service module.
Other orbit modules
The present form of the planned Euro-Russian CSTS (Crew Space Transportation System) also follows the three module layout of the Soyuz and will include an orbital module.