Two units of the standard Progress-M craft were modified as the Progress-M-VDU
to carry the VDU thruster units to the space station Mir.
The Progress cargo module is similar in construction to the Soyuz orbital module. The
cargo module carries pressurized cargo which the crew transfers into the station through
the docking hatch. After the cargo module is unloaded, trash, unwanted equipment, and
waste water can be loaded into the Progress for disposal when the spacecraft leaves the
Station.
In place of the Soyuz descent module, the Progress has a module containing propellant
tanks. For this special modification, the propellant module was replaced by a special
structure to carry the VDU thruster module. This was removed by the cosmonauts during a EVA to be
mounted on the Sofora mast. Due to this modification, these two Progress-M craft did not
carry fuel for the space station.
The Progress instrument-service module is similar to the module on Soyuz but the
pressurized instrument section is twice as long and contains additional avionics
equipment. The larger instrument section carries avionics which would be contained in the
descent module in the case of the Soyuz.
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