Low cloud at the Kennedy Space Center in Florida has prevented the shuttle Endeavour from launching on its latest mission to the space station.
Nasa officials stood the orbiter down with under 10 minutes left on the countdown clock.
Endeavour encountered no technical issues as it prepared to lift off and will try again on Monday morning.
It will be delivering a connecting unit and a large bay window to the international orbiting platform.
The shuttle mission is the first since President Barack Obama announced a new vision for US human space exploration.
Last Monday, he cancelled the rockets and capsule Nasa was developing to replace the shuttle, and urged the commercial sector to provide future transport needs.
The head of the US space agency, Charlie Bolden, was in attendance at Kennedy.Speaking to reporters, he conceded Mr Obama's new path was causing anxiety among Nasa workers and in Congress.
"This is going to be complex and complicated, and we've got to work all this stuff out," he said.
Endeavour's 13-day mission, which includes three spacewalks, will be the last night launch for a shuttle. The four missions that follow Endeavour will all take place in daylight hours.
Once installed on station, the Node 3 and Cupola modules will make the platform 90% complete.
The mission is an important moment for the European Space Agency's (Esa) contribution to the ISS project. Both modules being ferried to orbit were constructed in Italy by Thales Alenia Space.
Node 3 connecting unit will house the station's core life-support systems.
The node has several berthing ports that could conceivably even allow the ISS to be expanded one day.
"Node 3 is an interconnecting module," explained Simonetta Di Pippo, Esa's director of human spaceflight.
"It's a door open to the future, because if we decide to develop new modules, new extensions, new capabilities, we will be able to do it because we are now launching Node 3."
The Cupola is a dome-shaped module with seven windows. At 80cm (31.5in) in diameter, its top window will be the biggest ever flown in space.
The module will act as a control room to direct robotic operations on the exterior of the platform, and provide a vantage point for the astronauts to view their home planet.