The launch of the James Webb Space Telescope, which astronomers hope will herald a new era of discovery, was again pushed back Tuesday until at least Christmas Day due to "adverse weather conditions" at the launch site in French Guiana, NASA said.
The new target date, if determined to be viable, would be an actual Christmas gift for scientists who have been waiting three decades to see the largest and most powerful telescope take off for space aboard an Ariane 5 rocket.
The launch window on Saturday is from 1220-1252 GMT, the US space agency said.
"Tomorrow evening, another weather forecast will be issued in order to confirm the date of December 25," it said in a statement.
"The Ariane 5 launch vehicle and Webb are in stable and safe conditions in the Final Assembly Building."
It was the third time that the Webb telescope launch has been delayed, each time due to minor issues. The first was due to an accident during preparations for the launch in late November, and the second was due to a communications problem.
"Thank you to the teams... working overtime to ensure Webb's safe launch! The countdown to Dec. 25 is on," NASA Administrator Bill Nelson tweeted.
The Webb telescope follows in the footsteps of the legendary Hubble, but will orbit the Sun, rather than the Earth. It is hoped that the device will help answer fundamental questions about the Universe, peering back in time 13 billion years.
It will also give new information about nearly 5,000 exoplanets.
Shortly before the announcement of the delay, Nelson told a pre-launch briefing that Webb, which is named for a former NASA director, would be undertaking an "extraordinary mission."
"It's a shining example of what we can accomplish when we dream big," he said. "Webb will transform our view of the Universe."
Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate, said the launch would mark "the beginning of a new exciting decade of science, for NASA and for all of the international community."
The Webb telescope's orbit around the Sun will be 1.5 million kilometers (930,000 miles) from the Earth, much farther away than Hubble, which has been 600 kilometers above the Earth since 1990.