The looming external fuel tank (center) flanked by the solid rocket boosters on the launch pad. The shuttle is behind them.

The U.S. space agency has decided to return the space shuttle Atlantis to its hangar in Florida Monday morning to protect it from approaching Tropical Storm Ernesto.

NASA's decision comes after it again postponed the scheduled launch in Cape Canaveral, further delaying the shuttle's mission to the International Space Station. The scheduled launch of Atlantis was already delayed from Sunday to Tuesday because of a lightning strike.

Forecasters say Tropical Storm Ernesto could strike Florida at hurricane strength late Wednesday.

NASA says its launch window extends to September 13, but shuttle managers hope to launch by September 7 to avoid interfering with the scheduled launch of a Russian Soyuz rocket delivering a new crew to the space station. The shuttle's mission is essential to the construction of the space station.

Plans call for an 11-day Atlantis mission to the International Space Station, where astronauts will make three space walks to attach solar panels that will eventually generate one-quarter of the orbiter's energy.

Construction on the space station has been stalled since the shuttle Columbia disintegrated on re-entering Earth's atmosphere in 2003, killing all seven astronauts. NASA is under pressure to finish space station construction before the shuttle fleet is retired in 2010.