Three modules, different jobs

Shenzhou uses an orbital module, a reentry module and a propulsion module. Space and equipment for orbital work need not all return through the atmosphere. The architecture assigns different functions and different fates to connected parts, rather than bringing every item home inside one enormous protected cabin.

The Shenzhou 7 capsule in the photograph is a recovered reentry module. Its surviving surface and hatch can help explain a return vehicle, but its museum display omits the attached spacecraft sections used during orbital flight. Zhai Zhigang, Liu Boming and Jing Haipeng flew the complete spacecraft, not just the artifact on display.

Imagine a fictional design that puts its only return-control cable across a joint scheduled for separation. The team must change the design or the sequence before that joint is released. A module diagram becomes useful when you trace power, commands, people and propellant across its boundaries, including what must still work after separation.