Repaired, boosted to a new altitude and stocked with materials for future crews, the ISS is now ready for the expected July arrival of a new component, the Russian service module Zvezda.

Zvezda is to serve as living quarters for future crews and a propulsion unit for the space laboratory.

It will be launched from Baikonur cosmodrome in Kazakhstan by a Proton rocket, if the project remains on schedule.

The mooring of Zvezda is the next step in ISS assembly, a project in which 16 countries are participating.

The station currently comprises two units -- the US-built Unity module and the Russian module Zarya -- but is envisioned as having over 100 components once construction is completed.

To prepare for Zvezda's arrival, Atlantis Commander Jim Halsell and pilot Scott Horowitz boosted the station 43 kilometers (27 miles) to 374 kilometers (232 miles).

During a space-walk lasting close to seven hours, astronauts Jeff Williams and Jim Voss installed a camera cable and security handrails to the exterior of the station and replaced a faulty communications antenna.

The seven-member crew also completed assembly of a Russian-made mechanical arm; replaced a charger and batteries, smoke detectors and fire extinguishers; installed fans and computer cables; and conducted numerous tests.

And the team transferred more than a tonne of material onto the station, including computers, clothes, a stationary bicycle, a treadmill, and 180 liters (48 US gallons) of water.

The United States has scheduled three additional missions to supply the ISS, and Russia will send up the first ISS crew -- two Russians and a US astronaut -- before the end of the year.

The Atlantis mission is considered a shot in the arm for construction of the ISS, which, prior to the Atlantis visit, had not received a mission since June 1999.

It will take more than 40 additional missions to complete construction of the space lab according to its current schedule and design.

Construction is to be finished by the year 2005, with today's 30-tonne, two-unit station transformed into a 100-meter (yard) long complex of more than 100 components weighing more than 450 tonnes.

The launch of Zvezda will be a key milestone. It is already two years behind schedule, and a new delay will be a major setback for ISS construction plans.