The US space agency on Saturday postponed until September the launch of space probe Dawn on its eight-year mission to unlock the mysteries of the origins of our solar system.
It was the second delay for the mission in as many days.
"Primary reasons for the move were a combination of highly limited launch opportunities for Dawn in July and the potential impact to launch preparations for the upcoming Phoenix Mars Lander mission, set for early August," NASA said in a statement.
"A September launch for Dawn maintains all of the science mission goals a July launch would have provided," NASA further assured.
Dawn's launch was originally scheduled for Saturday, but because of weather was first delayed until Monday.
Even then, NASA said, a ship that was tasked with tracking the probe's launch into orbit would not have been in place by Monday as expected.
Dawn's eight-year mission will shed light on the earliest moments in the birth of the solar system 4.6 billion years ago by examining the two celestial bodies Ceres and Vesta in the asteroid belt between Mars and Jupiter.
Dawn is scheduled to enter orbit around Vesta in October 2011, proceed to Ceres in May 2012 and then begin orbiting Ceres in February 2015 -- traveling a total distance of 5.1 billion kilometers.
Dawn's launch window, said NASA earlier, will remain open until the end of October, when the two asteroids begin pulling away from each other, making a rendezvous with both practically impossible.
This will be the first NASA mission to orbit two separate objects.
NASA says the mission should provide a better understanding of the building blocks that formed the terrestrial planets and how the two "protoplanets" followed different evolutionary paths.
The space explorer, measuring 1.6m long and 1.3m wide when its solar array is retracted, is equipped with two spectrometers and a high-definition camera to study the two massive asteroids.
The Dawn project had once been canceled but NASA revived it in 2006 after an investment of US$449 million.