The spacecraft is protected by a heat shield that will keep it closer to room temperature, about 85 degrees Fahrenheit.
From Earth, it is 93 million miles (150 million kilometers) to the sun, and the Parker probe will be within 4 percent of that distance at its closest.
The launch was pushed back because a technical glitch on the rocket carrying the probe, United Launch Alliance's Delta IV Heavy rocket, caused NASA to run out the clock on its 65-minute launch window Saturday.
It was Parker who accurately theorized 60 years ago the existence of solar wind - the supersonic stream of charged particles blasting off the sun and coursing through space, sometimes wreaking havoc on electrical systems on Earth.
He said: "Wow, here we go!"
As the first rays of dawn reached Cape Canaveral on Saturday, the rocket that Nasa hopes will reveal the sun's secrets remained very much earthbound.
The new, 60-minute launch window opens at 3:31 am (0731 GMT) for the Parker Solar Probe, a $1.5 billion unmanned spacecraft that aims to get closer than any human-made object in history to the center of our solar system.
"The team received a gaseous helium reg pressure alarm that kicked them out", said Mic Woltman with NASA's Launch Services Program.
"The sun is full of mysteries", said Nicky Fox, project scientist at the Johns Hopkins University Applied Physics Lab. "We have not been able to answer these questions".
The device will measure the electromagnetic field of the Sun and determine the nature of the particles emitted by the star. If the process doesn't go smoothly, the team will be looking at a 48-hour turnaround and launching early on August 13. When it nears the Sun, the probe will travel rapidly enough to go from NY to Tokyo in one minute - some 688,000kmh - making it the fastest human-made object.
"To me, it's still mind-blowing", she said.
"Since this is a mission into unknown territory, we have to be prepared for some surprises, things we never thought of or things we thought of but were not correct", he said in a recent briefing.
The Parker Solar Probe is equipped with four instruments.
The spacecraft's heat shield will serve as an umbrella, shading the science instruments during the close, critical solar junctures.