Spacewalks usually last about six-and-a-half hours, but Friday's was "abbreviated" due to the late start and lasted four hours and 13 minutes, Navias said.
The pair completed all the major work scheduled for the day, with the exception of a couple of minor tasks, he said.
The main job was to replace what is known as the ExPRESS Carrier Avionics, or ExPCA, box.
It weighs 200 pounds (91 kilograms) on Earth and routes data and commands to experiments inside the space station, Navias said.
"It has been exhibiting some thermal issues of late, so it is being replaced," he said.
Fischer's enthusiasm for the beauty of the Earth beneath him was apparent throughout the spacewalk.
"Ooh, it's the Bahamas!" he fawned at one point.
"Oh, they are my favorite. Wow, they're so blue," added the rookie spacewalker, who goes by the nickname "2Fish."
Whitson, who was making the ninth spacewalk of her career, could often be heard chuckling at Fischer's exclamations.
She holds the record for most spacewalks by a woman, and ranks fifth for the most hours spent in space by an astronaut, with 57 hours and 35 minutes.
As the spacewalk concluded, Whitson said it was "amazing" to have completed the station's 200th spacewalk. "It is a huge honor to work with all of you."
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The first piece of the International Space Station — a Russian module — was launched in 1998, and the first spacewalk ever conducted at the station took place in December that year.
Today, the $100 billion orbiting lab is roughly the size of a football field and a symbol of global cooperation among the 15 nations that have helped build and operate it.
The station orbits the Earth at a height of about 250 miles (400 kilometers), circling the planet every 90 minutes at a speed of about 17,500 miles (28,000 kilometers) per hour.
NASA has experienced a series of problems with water leaking inside the astronauts' helmets, most notably in 2013, when water began filling Italian Luca Parmitano's headpiece, forcing him to cut short his spacewalk and make an emergency re-entry into the space lab.
NASA's bulky white spacesuits are aging, and the same models have been in use for four decades.
Despite the glitch that delayed the start of today's spacewalk, Navias said the suits performed "flawlessly" during the outing.
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