"Launch teams are working on technical issues and weather is predicted to be 70 per cent chance of favourable conditions", NASA said in a tweet late on Thursday.
The car-sized probe is created to give scientists a better understanding of solar wind and geomagnetic storms that risk wreaking chaos on Earth by knocking out the power grid.
NASA on Saturday postponed the launch of a Delta IV Heavy rocket carrying the Parker Solar Probe spacecraft, created to probe the Sun.
The launch now is planned for Sunday, August 12, from Space Launch Complex-37 at Cape Canaveral Air Force Station.
The probe, the size of a small auto, is due to make a seven-year mission to skim through the sun's atmosphere, enduring temperatures of 1,300C.
The rocket with the Parker Solar Probe moments before a problem caused the launch to be delayed.
The countdown finally came out of a built-in hold at the T-minus four-minute mark, ticking toward a launch attempt at 4:28 a.m. when an engineer called out "hold, hold, hold" at the T-minus one-minute 55-second mark.
By coming closer to the Sun than any spacecraft in history, the unmanned probe's main goal is to unveil the secrets of the corona, the unusual atmosphere around the Sun.
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Scientists hope the mission will be able to provide answers as to why the corona is 300 times hotter than the surface of the sun, a phenomenon that Nasa says is in "defiance of all logic" because "its atmosphere gets much, much hotter the farther it stretches from the sun's blazing surface".
Parker's lightweight heat shield is just 4 ½ inches (11 centimeters) thick.
The spacecraft's path to the sun runs past Venus.
"The sun is full of mysteries", said Nicky Fox, project scientist at the Johns Hopkins University Applied Physics Lab.
But getting so close to the Sun requires slowing down - for which Parker will use the gravity of our neighbor planet, Venus.
"The Parker Solar Probe will help us do a much better job of predicting when a disturbance in the solar wind could hit Earth", said Justin Kasper, a project scientist and professor at the University of MI.
At Parker Solar Probe's closest approach to the Sun, temperatures on the heat shield will reach almost 1,371 degrees Celsius, but the spacecraft and its instruments will be kept at a relatively comfortable temperature of about 29.4 degrees Celsius. "Each time we fly by we get closer and closer to the Sun", Driesman added.