Nasa astronaut Jeff Williams performed leak checks and installed hardware to monitor and support Beam expansion set to begin at 6.30pm (India time). The expansion could potentially start earlier, Nasa said in a statement.
Meanwhile, a new trio of ISS crew members is ready in Russia for final qualification exams for a mission set for launch on June 24.
Cosmonaut Anatoly Ivanishin will command the new Soyuz MS-01 spacecraft carrying Nasa astronaut Kate Rubins and Jaxa astronaut Takuya Onishi.
Nasa Television will broadcast the expansion activities live. Crew entry into Beam, which has an expanded habitable volume of 565 cubic feet (16 cubic metres), is planned for June 2.
The Dragon spacecraft was taken by ship to Long Beach where some cargo was removed and returned to Nasa for processing.
On April 17, engineers at Nasa Johnson Space Centre in Houston used the ISS's high-tech robotic arm to pluck Beam from the back of the SpaceX Dragon cargo ship that reached the space station on April 11 and added it onto the orbiting laboratory complex.
At the time of installation, the space station was moving over the Southern Pacific Ocean at an altitude of about 350 km from the Earth's surface. It will remain attached to the station for the two-year test period, US space agency Nasa had written in a blog.
Nasa is investigating concepts for habitats that can keep astronauts healthy during space exploration and Beam will be the first test of such a module attached to the space station.
It will allow investigators to gauge how well it performs overall and how it protects against solar radiation, space debris and the temperature extremes of space.
Expandable habitats require less payload volume on the rocket than traditional rigid structures and expand after being deployed in space to provide additional room for astronauts to live and work inside.
After the testing period is completed, Beam will be released from the space station to eventually burn up harmlessly in the earth's atmosphere.
The 1,400 kg Beam is a 17.8 million dollar project to test the use of an inflatable space habitat in micro-gravity.
A total of six astronauts are already on-board the ISS along with another US commercial cargo ship called Cygnus that has been attached to the station since March 26.