Design
Progress is of much the same size and shape as Soyuz. It consists of three modules:
- A pressurized forward module. This carries the supplies for the crew such as scientific equipment, clothes, prepackaged and fresh food, and letters from home. The docking drogue is similar to that of the Soyuz but features ducting for the UDMH fuel and N2O4 oxidiser.
- A fuel compartment. The reentry module of the Soyuz was replaced with an unpressurized propellant and refueling compartment with ducting along the outside of the spacecraft. This meant that if a leak occurred, the poisonous gas would not enter the station's atmosphere. The fuel is carried in two tanks.
- A propulsion module. The propulsion module, at the rear of the spacecraft, remained unchanged and contains the orientation engines used for the automatic docking. It may be used to boost the orbit of the station once docked.
Reduction in mass was possible because the Progress was designed to be unmanned and disposable. This means that there is no need for bulky life support systems and heat shields. The spacecraft also has no ability to split into separate modules. After undocking, the spacecraft performs a retrofiring and burns up in the atmosphere.
Read more about this topic: Progress (spacecraft)
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