To a relieved burst of applause at mission control, the 320-million-dollar Zvezda module docked automatically at 0045 GMT after a year-long delay caused by severe cash constraints in Russia's once proud space program.

The first mission may now fly to the ISS in October, although the giant station -- which will eventually be visible from Earth -- will not be completed for another five years.

The Zvezda, or Star, module is now linked up to the first Russian element called Zarya and the US-built Unity.

It will also house the navigation and guidance systems until another US module assumes those functions.

"Today is a great day, because a project which we have worked on for six years has been successfully completed," said Russia's space agency director Yury Koptev, who exchanged congratulations by phone with NASA administrator Daniel Goldin.

US National Aeronautics and Space Administration (NASA) official in Korolev, Robert Castle, was clearly pleased by the successful docking. "It's the start of a new era," he said.

Yury Semyonov, president of Energia the Russian company which built Zvezda, called it a "key moment" in the development of the space station.

Zvezda was financed almost entirely by the Russians. However, the US fast food giant Pizza Hut has alleviated some of the financial difficulties in return for having its logo emblazoned on the side of the launcher rocket.

The publicity stunt is reportedly costing Pizza Hut one million dollars, the Russian business daily Kommersant reported, but the space agency has refused to confirm the sum.

The first Zarya module was built in Russia, but financed entirely by the US. The International Space Station is a project involving 16 countries, including the United States, Canada, Japan and Russia. When finished, the complex will be 100 meters (yards) long, and weigh more than 450 tonnes.

The stage is now set for the first ISS team of US commander William Shepherd and Russian cosmonauts Yury Gidzenko and Sergei Krikalyov will blast off on the Russian space craft Soyuz on October 30.

Zvezda's launch on July 12 had been delayed for a year due to financial and technical problems. The giant floating laboratory is expected to remain in service until 2013.