HOUSTON -- Seven shuttle astronauts will say their orbital goodbyes to the three-person crew of the International Space Station (ISS) after a busy week of construction aboard the high-flying laboratory.
The STS-116 astronaut crew of NASA's shuttle Discovery is due to cast of from the space station at 5:09 p.m. EST (2209 GMT) to begin the trek back to Earth following an intense eight days of docked operations [video].
"We only have only more major objective to complete," said John Curry, NASA's lead ISS flight director for Discovery's STS-116 mission.
That objective, he added, is undocking.
The space station's Expedition 14 crew and Discovery's STS-116 astronauts will spend this morning transferring some final items between their two spacecraft. They are expected to hold a brief farewell ceremony before shutting the hatches between their two vehicles at 1:57 p.m. EST (1857 GMT).
Because of a spacewalk Monday, the two astronaut crews had one extra day to work alongside each other 220 miles (354 kilometers) above Earth.
"There's no such thing as a bad day in space," Discovery's STS-116 commander Mark Polansky told reporters in an interview on NASA TV. "So I think everybody is happy to maximize the experience."
Discovery's crew delivered a small, but vital, addition to the space station's main truss and performed four spacewalks -- including Monday's unplanned excursion -- to install it, rewire the orbital laboratory's power grid and furl a stubborn solar array that ultimately took some prodding to stow.
"We really like to have a day between the last spacewalk and undocking normally," Curry said, adding that the final spacewalk to added an extra heavy duty work day to the joint crew's schedule. "We know we'll be able to get everything accomplished. They're just going to have to press, you know, there's not going to be a lot of celebration time on orbit for them."
To ease some of that strain, mission managers have pushed back Discovery's undocking to a later time than typical of shuttle departures, mission managers said. But the change did mean the astronauts will not have enough time to fly completely around the ISS, they added.
Known as a flyaround, the maneuver is typically performed, given adequate time and propellant supplies, to allow a photography session to document the space station's new appearance -- now with one solar wing stowed and a new spacer on its port side -- for use by engineers and release to the public.
"We're not going to do the full flyaround," Curry said. "We're just going to fly up to the top and then [separate]."
Discovery is also leaving the ISS with a different crew complement than when it arrived.
One STS-116 astronaut, mission specialist Sunita Williams, is remaining aboard the station as a flight engineer alongside Expedition 14 commander Michael Lopez-Alegria and flight engineer Mikhail Tyurin. She is exchanging roles with European Space Agency astronaut Thomas Reiter, who has lived aboard the ISS since July, and nearing the end of his ISS mission.
"I've been living here now for a long time and this has become a home," Reiter said of his ISS departure. "So it will be a little bit of a sad moment to leave my colleagues up here."
Reiter and the rest of Discovery's STS-116 crew are due to return to Earth Friday, with touchdown at NASA's Shuttle Landing Facility at the Kennedy Space Center in Cape Canaveral, Florida set for 3:56 p.m. EST (2056 GMT).
- VIDEO: STS-116 Mission Profile: Undocking
- Images: The Spacewalks of NASA's STS-116
- Images: Discovery's STS-116 Launch Day Gallery
- STS-116 Video: Power is Everything
- STS-116 Video: Building Blocks
- Mission Discovery: The ISS Rewiring Job of NASA's STS-116
- Complete Space Shuttle Mission Coverage
- The Great Space Quiz: Space Shuttle Countdown
- All About the Space Shuttle