The FGB module provided the TKS with living space, storage racks for equipment and supplies to be delivered to the Almaz station, propulsion, and electricity. Derivatives of the FGB were the add-on modules to the Mir station, as well as the first module of the International Space Station.

Total combination of propellant and payload in internal racks that could be carried with the VA attached was 6700 kg. Up to 4528 kg of payload or 3822 kg of propellant could be carried. Disposable payload with standard equipment, VA, and full propellant load 1600 kg. A typical unmanned mission to Salyut carried 2700 kg of payload and 3822 kg of propellant. The FGB was entered from the VA capsule via a short tunnel at the forward end of the pressure vessel. At the aft end a pilot's station was equipped with controls and windows for manual docking with the Almaz space station. The docking port was also located here. Operational TKS would have delivered KSI film return capsules to Almaz stations. These would have been located around the docking port and grappled by a small manipulator arm on the Almaz for transfer to the film capsule airlock for loading.