NASA canceled the Friday return of the space shuttle Atlantis to Earth due to bad weather at the Kennedy Space Center in Florida and said landing could happen Saturday at the earliest.
After an initial delay for Friday and then a cancellation, the US space agency retargeted touchdown for a second landing opportunity Saturday at 9:16 am (1316 GMT).
"The weather would not cooperate today," a NASA spokesman said.
Atlantis, which blasted off on May 11 with a crew of seven astronauts on mission to repair the Hubble space telescope, had been scheduled to touch down at 10:00 am (1400 GMT).
NASA then set a second landing opportunity at 11:39 am (1539 GMT) but poor weather "continues to be a concern," it said before cancelling the attempt on Friday altogether.
When flying 500 kilometers (311 miles) above Florida, the American astronauts saw what awaited them on Earth: cloudy skies, strong winds and possible thunderstorms.
A final decision to cancel Friday's return was made about two hours before the shuttle was due to land.
NASA has set several conditions for a landing: the cloud cover in the skies must not be more than 50 percent, visibility must be at least eight kilometers (five miles) and lateral winds must not be blowing at more than 28 kilometers an hour (17 miles an hour).
Atlantis and its seven-strong crew are returning from a successful 11-day mission to repair and restore the Hubble space telescope to allow it to continue its ground-breaking exploration of the universe for at least another five years.
So far, NASA has ruled out using Edwards Air Force Base in California as a back up landing point as it would mean flying the shuttle back to Florida on a Boeing 747, involving substantial extra cost.
The observatory was released on Tuesday after five obstacle-filled spacewalks.
The enhancements have equipped Hubble to search for the earliest galaxies, probe the mysteries of dark matter and dark energy as well as study planet-making processes.
But the trouble was well worthwhile.
John Grunsfeld, an astronomer turned astronaut who led three of the mission's five spacewalks, told lawmakers Thursday that Hubble "is probably the most significant science instrument of all times."
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