The wings were rolled slowly to avoid the possibility of snagging
Ten years after its construction began, the International Space Station now has full power capability.
Mission controllers commanded the unfurling on Friday of the platform's fourth and final pair of solar arrays.
The huge solar wings had been delivered to the ISS by the Discovery shuttle and installed by its astronauts with the help of the station's robotic arm.
When taken up to full capacity, the station's arrays should now generate as much as 120 kilowatts of electricity.
The addition of the final set of solar wings will double the amount of power available for scientific experiments aboard the station - from 15kW to 30kW.
Nasa flight director Kwatsi Alibaruho describes the unfurling
The unfurling of the 73m-long (240ft) structures went very smoothly.
"It's just really amazing," commented Mike Fincke, the space station's commander. He said there was "a shout of triumph" from astronauts aboard the linked station-shuttle complex once the two wings were fully extended.
When viewed from the Earth's surface shortly after sunset, the ISS appears as a very bright star moving swiftly across the sky. The addition of a larger reflective area will make the platform an even more brilliant spectacle.
The fourth set of solar arrays is attached to the sixth starboard truss, or backbone segment, of the platform which was bolted into place on Thursday. The work took spacewalking astronauts Steve Swanson and Richard Arnold six hours and seven minutes to complete.
Richard Arnold helped bolt down the new backbone segment
The entire ISS backbone - which supports not just the arrays, but radiators and other equipment - now stretches for 102m (335ft).
The solar wings are the last major pieces of US-made hardware to be attached to the station.
Their addition increases the mass of the platform to just over 300 tonnes (670,000 pounds). The station is now more than 80% complete.
Outstanding items include significant European contributions, such as the Node 3 connecting unit, the Cupola window and the European robotic arm.
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