CAPE CANAVERAL, Fla. - Seven astronauts aboard NASA's Discovery shuttle will have to wait at least two more days to rocket towards the International Space Station (ISS) after poor weather foiled a Thursday night launch attempt.

"Okay Roman, we gave it the best shot," NASA launch director Michael Leinbach told STS-116 commander Mark Polansky. "We are going to have to declare a scrub at this time."

"Mike, we understand, thanks to the team for all the hard work," replied Polansky, whose callsign is Roman. "Try not to be too disappointed and we will be ready to support the next time we get a chance."

Launch time is now set for Saturday at 8:47:34 p.m. EST (0147:34 Dec. 10 GMT).

Discovery's STS-116 astronaut crew planned to launch at 9:35:48 p.m. EST (0235:48 Dec. 8 GMT), but thick clouds prompted a one-day delay in the ISS construction mission. A heavy cloud layer, with clouds estimated at 500 feet thick, violated NASA's flight rules today's space shot, launch officials said.

Launch controllers opted to forgo a Friday attempt to loft Discovery due to a dismal weather forecast of low clouds, rain showers and high crosswinds that give any attempted space shot only a 10 percent chance of lifting off.

"The weather for Saturday is slightly better," NASA launch commentator Bruce Buckingham said.

Weather forecasts still predict clouds, showers and crosswinds for Saturday's launch attempt, but Discovery's odds of favorable launch conditions increase to 30 percent, Buckingham added.

Discovery's STS-116 astronauts were already tucked inside the spacecraft's crew cabin when launch controllers scrubbed today's planned space shot. Aboard with Polansky were pilot William Oefelein and mission specialists Robert Curbeam, Nicholas Patrick, Joan Higginbotham, Sunita Williams and European Space Agency (ESA) astronaut Christer Fuglesang.

They are hauling a new piece of the space station's portside truss for installation during their planned 12-day spaceflight. They also plan to stage three spacewalks at the ISS to secure the new addition and rewire the orbital laboratory's power grid into its final configuration.

One STS-116 crewmember, mission specialist Sunita Williams, will relieve European Space Agency astronaut, Thomas Reiter, who has been aboard the orbital laboratory since July. Reiter will ride back to Earth aboard Discovery in Williams' place.

Discovery's launch window currently runs from Dec. 7 to 17, and could be extended to Dec. 26 if mission managers approve the shuttle for flight during the year-end switch from 2006 to 2007.

Launch time is pushed back about 23 minutes for every day of delay, so that the spacecraft can reach the ISS, which is orbiting about 220 miles (352 kilometers) above Earth at a rate of about five miles per second.

SPACE.com staff writer Tariq Malik contributed to this story from New York City.