Fully unfurled, the solar wings make Alpha - this is the unofficial name Expedition 1 have given to their new home - one of the brightest "stars" in the night sky.
The craft landed at the Kennedy Space Center just after 1800 local time (2300 GMT) having completed 170 orbits.
"Outstanding job. Welcome back," said mission control, speaking to Endeavour's commander, Brent Jett, once the shuttle had come to a stop on the illuminated runway.
Endeavour attached a solar power unit, complete with two giant light-collecting wings, to the exterior of the ISS. The power system will substantially improve day-to-day conditions on the platform for its current residents, American astronaut Bill Shepherd and his Russian colleagues Sergei Krikalev and Yuri Gidzenko.
Difficult weeks
The visit was a welcome respite for the Expedition 1 crew from some difficult weeks spent installing, testing and repairing the station's life support systems.
But thanks to the new electricity-producing solar wings, which stretch 73 metres (240 ft) from tip to tip, the men no longer have to conserve power aboard the space station.
They also now have access to the entire three-room complex; one room had been sealed off because there was not enough power to heat it.
"They look surprisingly good," remarked Brent Jett. "They've been running some nights on only four hours of sleep. I was just really impressed, you know, how well they got along with each other."
Fully unfurled, the solar wings make Alpha - this is the unofficial name Expedition 1 have given to their new home - one of the brightest "stars" in the night sky.
Shuttle astronauts Joe Tanner and Carlos Noriega went outside the orbiter to set up the new power system - the biggest and most powerful ever deployed in space.
Three spacewalks were required to install the $600m system, unfurl its panels, hook up all the cables and then tighten one slack wing.
Endeavour's astronauts also spent one day inside the ISS, helping Expedition 1 with computer problems and cargo transfers.
Extended stay
Bill Shepherd and his crewmates have now been aboard the space station for a month and have at least three more months to go before they return to Earth.
The American space agency, Nasa, announced on Endeavour's return that Expedition 1's stay would be extended for a few weeks to allow engineers to repair faults on the orbiter that is scheduled to bring the crew home.
The next construction phase on the ISS occurs in January when the American-made lab Destiny is attached to the platform. The lab will be taken into orbit by the space shuttle Atlantis.
The multi-billion-dollar space station project is a partnership of the United States, Russia, Europe, Japan, Canada and Brazil. Completion is targeted for 2006, when rotating teams of up to seven researchers are expected to be able to live aboard the station in a pressurised environment with roughly the space of a 747 jumbo jet.