https://en.wikipedia.org/wiki/Zvezda_(ISS_module)Zvezda (Russian: ЗвездаÌ, meaning "star"), Salyut DOS-8, also known as the Zvezda Service Module, is a module of the International Space Station (ISS). It was the third module launched to the station, and provides all of the station's life support systems, some of which are supplemented in the US Orbital Segment (USOS), as well as living quarters for two crew members. It is the structural and functional center of the Russian Orbital Segment (ROS), which is the Russian part of the ISS. Crew assemble here to deal with emergencies on the station.[7][8][9]
The module was manufactured by RKK Energia, with major sub-contracting work by GKNPTs Khrunichev.[10] Zvezda was launched on a Proton launch vehicle on 12 July 2000, and docked with the Zarya module on 26 July 2000.
The basic structural frame of Zvezda, known as "DOS-8", was initially built in the mid-1980s to be the core of the Mir-2 space station. This means that Zvezda is similar in layout to the core module (DOS-7) of the Mir space station. It was in fact labeled as Mir-2 for quite some time in the factory. Its design lineage thus extends back to the original Salyut stations. The space frame was completed in February 1985 and major internal equipment was installed by October 1986.
The Mir-2 space station was redesigned after the failure of the Polyus orbital weapons platform core module to reach orbit. Zvezda is around ​1â„4 the size of Polyus, and has no armaments.
The Mir space station and Zvezda had the same design problem of launching with all the hardware permanently installed. Russian (and Soviet) space doctrine has always been to fix the hardware onboard instead of simply replacing them like the US Orbital Segment (USOS) does with the 41.3 inch (105 cm) wide International Standard Payload Racks that can easily fit through the 51 inch (130 cm) wide hatch openings through the modules connected via the Common Berthing Mechanism (CBM). This means broken but unfixable hardware onboard the Mir modules and Zvezda end up being stuck there forever and can't be replaced. ESA Italian astronaut Luca Parmitano in 2020 said that the originally installed computers in Zvezda don't work anymore and the central command post's computers are now three Lenovo ThinkPad laptops. The broken computers' monitors, keyboard, and other devices are left there as it is but cannot be removed and replaced. The pre-installed Elektron oxygen generating system also has to be fixed frequently by cosmonauts instead of simply being replaced due to the problem of Zvezda's 78.74 cm (31 inch) wide hatch and the inability to replace the Elektron with another Elektron. Another reason why Elektrons can't be replaced is because the three Elektron units that were launched on Zvezda were the last units ever manufactured. The original manufacturers went out of business and the single engineer who made the tweaks for the Elektrons that were installed on Zvezda died with all his secrets and knowledge not passed to anybody else. In October 2020, the Elektron system malfunctioned yet again and had to be deactivated.
