Kvant-2, the second module to be attached to Core Module (in November 1989) is
known as the "Enhancement module" or the "Scientific and Airlock module." It is
reached from the Transfer Node at the end of the Core Module. Kvant-2 provides
a porthole for Earth observation photography, and an exit hatch for EVA
(extravehicular activity, or spacewalks).
Over 40 feet long and 14 feet in diameter, Kvant-2
has three hermetic compartments. The main compartment has various apparatus,
including two oxygen generators, to bring the entire complex closer to a
closed-cycle environment. There is also a cubicle with a toilet. In an
ingenious recycling scheme (water, like other supplies, is precious on Mir),
used water is pumped through a column containing ion-exchange resins and
activated charcoal, then is filtered, remineralized, purified, and reused by
the hygiene system.
At the far end of the module is the airlock, with a hatch wider than a docking
port, which the cosmonauts use to access the outside of Mir during EVAs. Two
Orlan-DMA spacesuits are stored in the airlock for that purpose.