Although fully prepared for the launch of the STS-126 mission to the International Space Station, it looks like NASA will have weather conditions to fear this time as well, just like on most missions. Endeavour is scheduled to launch on Friday at 7:55 p.m. EST, but a cold front bringing clouds and rain could force the agency to postpone the liftoff.

On Tuesday, the seven astronauts of the STS-126 arrived at the Kennedy Space Center in preparation for the Friday launch. The agency began the countdown for the launch on Tuesday night, but weather conditions appear to leave just 60 percent chances of favorable weather for the launch. A second launch window could open up on Sunday, weather specialists informed.

The STS-126 mission is of extreme importance for the agency, as it has been planned for years to be an “expansion mission” for the International Space Station, in the sense that it will offer the possibility for the station to support twice the crew it currently has. In addition to that, the STS-126 mission will also need to solve the problem of the power necessary to support three extra members on the ISS.

NASA explained that STS-126’s 15-day mission is to prepare the station for the expansion, by carrying a multi-purpose logistics module loaded with 32,000 pounds of equipment. “It’s the most jam-packed logistics module we have ever carried up there,” STS-126 Commander Chris Ferguson explained. “We’re taking a three-bedroom, one-bathroom house and turning it into a five-bedroom, two-bathroom house with a gym.”

Spacewalkers Heidemarie Stefanyshyn-Piper, Steve Bowen and Shane Kimbrough will have the mission to fix the problem with one of the station’s solar alpha rotary joints, which presents more vibrations than it should and needs more power to rotate due to insufficient lubrication. The engineers explained that without lubrication, the trundle bearing assemblies holding the two halves of the joint together press too hard against one side of the joint, which could cause further damage.

The other members of the crew, namely Pilot Eric Bow, Mission Specialist Donald Pettit and the station’s next flight engineer Sandra Magnus, will be busy working inside, unpacking the new crew quarters, a new toilet, a new kitchen, a new refrigerator and new exercise equipment.

NASA believes expanding the number of astronauts on the International Space Station is an important step toward using the station to its full capacity, as well as making it less dependent on the space shuttle. The new regenerative environmental control and life support system will give the station the ability to recycle urine and the condensation that the crew breathes into the air into pure water that can be used for drinking or to cool the station’s systems.

The plan is to make the transition to a six-person crew on International Space Station’s 10th anniversary, on November 20, NASA said. “It’s been a tremendous international effort to get to this point, and I can’t think of a better way to celebrate it,” said lead shuttle flight director Mike Sarafin.