Four more shuttle missions remain to stock the station and deliver science experiments before NASA retires its three-ship fleet later this year. The station, a $100 billion project of 16 nations, has been under construction 220 miles (352 km) above Earth since 1998.
With pilot Terry Virts at the controls, Endeavour departed the station at 7:54 p.m. EST (0054 GMT on Saturday), 10 days after arriving with the Tranquility connecting hub and the dome-shaped cupola, which is outfitted with seven windows to provide a nearly 360-degree view outside the station.
The new rooms were hooked up during three spacewalks by Endeavour astronauts Robert Benhken and Nicholas Patrick.
"It's so hard to put into words the view that we see out those beautiful seven windows," crewmate Kay Hire said during an in-flight press conference. "It's comparing a black-and-white analog picture to a super high-def color picture. It's just phenomenal." NASA extended Endeavour's stay at the station a day to give the station crew more help setting up equipment inside Tranquility, which will serve as a second living module.
A toilet, water recycling system, oxygen generator, air scrubber and exercise gear already have been relocated into the new hub. NASA still is struggling to get the water purification system working, however, and has told the station crew to only use the Russian toilet until further notice.
The water recycling system collects urine, condensate and other wastewater and turns it into potable water for drinking and cooking. With the shuttle missions ending due to safety concerns and high operating costs, the station will have to become much more reliant on reusing its water.
Russian, European and Japanese cargo ships will keep the station resupplied but none have the lift capacity of the shuttle, nor its ability to produce water - a byproduct of the electrical system - in orbit.
NASA already has turned over crew transport to Russia and plans to invest $6 billion in the next five years in commercial US firms, hoping to spark development of orbital passenger spaceflight services.
The agency also announced this week it plans to spend $75 million over the next five years for commercial suborbital spaceflights for science experiments and educational payloads.
Virgin Galactic, an offshoot of Richard Branson's Virgin Group, debuted its first passenger spaceship in December. At least four other firms are working on suborbital ships for tourists, researchers and businesses.
Endeavour and its six-member crew, which also includes commander George Zamka and flight engineer Stephen Robinson, are due back at the Kennedy Space Center at 10:16 p.m. EST on Sunday (0316 GMT on Monday).
