NASA's car-sized robe was scheduled to launch on a Delta IV Heavy rocket from Cape Canaveral, Florida during a 65-minute launch window.
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.
The launch now is planned for Sunday, August 12, from Space Launch Complex-37 at Cape Canaveral Air Force Station.
A $1.5 billion Parker Solar Probe mission will fly through the sun's outer atmosphere within 6.4 million km of the big hot star repeatedly, gathering key insights about solar structure, activity, atmosphere, solar winds and other features.
Rocket maker United Launch Alliance said it would attempt the launch again today, provided the helium-pressure issue can be resolved quickly.
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.
The probe will be 3.9 million miles from the sun's surface, making it the closest spacecraft to the sun's surface in history.
The spacecraft eventually will run out of fuel and, no longer be able to keep its heat shield pointed toward the Sun, will burn and break apart - except perhaps for the rugged heat shield.
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Parker's lightweight heat shield is just 4 ½ inches (11 centimeters) thick.
The probe will be controlled from the Mission Operations Centre based at the Johns Hopkins University Applied Physics Laboratory (JHU APL), which is where NASA handles its unmanned missions.
NASA has delayed the launch of a probe which will make a series of unprecedented orbits of the sun.
Even in a region where temperatures can reach more than a million degrees Fahrenheit, the sunlight is expected to heat the shield to just around 2,500 deg F (1,371 deg C).
But getting so close to the Sun requires slowing down - for which Parker will use the gravity of our neighbor planet, Venus.
The tools on board will measure the expanding corona and continually flowing atmosphere known as the solar wind, which solar physicist Eugene Parker first described in 1958.
"We will fly by Venus seven times throughout the mission". The current close-to-the-sun champ, NASA's former Helios 2, got within 27 million miles (43 million kilometers) in 1976.