The transfer compartment (Russian: Переходный Отсек, ПхО, romanized: Perekhodniy Otsek, PKhO) has three docking ports, along with a internal hatch that can seal it off from the rest of the module, allowing it to serve as an airlock.

The transfer compartment's airlock functionality was only used once during Expedition 2, when Yury Usachov and James Voss put a docking cone on the nadir port to prepare for the arrival of the Pirs module.

The forward, small-diameter instrument compartment (Russian: Приборой Отсек, ПО, romanized: Priboroi Otsek, PO) contains the station command post (central computer) and related equipment, The aft large-diameter habitable compartment (Russian: Жилой Отсек, ЖО, romanized: Zhloi Otsek, ZhO) contains two sleeping quarters, a NASA-provided Treadmill with Vibration Isolation Stabilization, a kitchen equipped with a refrigerator/freezer and a table, a bicycle for exercise, a toilet and other hygiene facilities, this section also contained the Elektron system that electrolyzes condensed humidity and waste water to provide up to 5.13 kilograms (11.3 lb) per day of oxygen for breathing, while hydrogen is expelled into space.

The large movable "Lira satellite communications antenna" is located on the Zvezda service module near the aft or rear of the International Space Station on this Assembly Compartment.

[6] The oxidizer used for the propulsion system is dinitrogen tetroxide and the fuel is UDMH, the supply tanks being pressurised with nitrogen.

The Zvezda module inherited a limitation from its predecessor Mir and Salyut stations rooted in a Soviet spacecraft design philosophy favoring the permanent installation of critical hardware.

A notable example is the pre-installed Elektron oxygen-generating system, which required frequent repairs by cosmonauts due to the inability to replace it.

[18][19][20][21][22] The rocket used for launch to the ISS carried advertising; it was emblazoned with the logo of Pizza Hut restaurants,[23][24][25] for which they are reported to have paid more than US$1 million.

[26] The money helped support Khrunichev State Research and Production Space Center and the Russian advertising agencies that orchestrated the event.

Structural construction was performed by RKK Energia, then handed over to the Khrunichev Design Bureau for final outfitting.

Joint reviews between the Russian Space Agency (Roscosmos) and the NASA ISS Program Office monitored construction, solved language and security concerns and ensured flight readiness and crew training.

Due to this risk, NASA had constructed an Interim Control Module (ICM) in case it was delayed significantly or destroyed on launch.

The source appears to be microscopic structural cracks within the small transfer tunnel, known by the Russian acronym PrK, which connects Zvezda to the aft docking port typically used by Progress cargo spacecraft.

NASA has classified the leaks as a high-risk threat to spaceflight activities, potentially leading to "catastrophic failure."

However, Roscosmos says that it does not believe a catastrophic disintegration of the PrK is realistic, and has expressed confidence in their ability to monitor and manage the leak.

[32][33][34] As of November 2024[update], to mitigate the leak and the risk of a catastrophic failure the normal operating procedure is to keep the hatch leading to the PrK from Zvezda closed except when a spacecraft is being actively accessed.