At 9:22am Eastern today, the Russians will launch a modified Progress cargo ship to ferry a module to the slowly growing International Space Station. Dubbed Poisk (the Russian for “Search,” or “Explore”) the module’s primary function will be to act as an additional docking port for crewed Soyuz and uncrewed Progress and European ATV spacecraft.

The extra port is needed because the ISS crew grew from three to six in May. Two Soyuz spacecraft (each of which seats three) must remain docked to the station in case of a catastrophic accident that forces the entire crew to return to Earth. As a result, there is only one free port remaining to handle any incoming spacecraft bringing supplies or replacement crew members.

The Poisk module is largely a duplicate of the Piers docking module already attached to the ISS. In addition to a docking port, both modules can also act as airlock for spacewalkers. Unlike Piers, some hookups have been added inside Poisk that will allow research racks to be installed later, which is why NASA and the Russian space agency are calling Poisk a “mini-research module”. The hookups are something of a face-saving exercise for the Russians, as they were forced to cancel plans for an ambitous research module earlier in the decade due to budget cuts, and in fact Russia has not added a new module to the ISS since Piers was sent aloft in 2001. However, Russia is currently working on a more sophisticated laboratory module, called Nauka, which it hopes to launch in December 2011. Nauka is being constructed from the backup module to the Zarya module, which was launched in 1998 as the founding element of the ISS.

[Update: 11:50 am] – Poisk was launched successfuly and will rendezvous and dock with the ISS on Thursday. The docking will be televised live on NASA TV, starting at 10am Eastern.