The probe was expected to launch early Saturday morning but was delayed twice, once at 3:53 a.m. and again at 4:28 a.m., during the 65-minute launch window that began at 3:33 a.m. ET.
The Parker Solar Probe, named after American solar astrophysicist Eugene Parker, will, as the U.S. space agency describes it, "touch the sun" as it flies within 3.9 million miles of the star's surface.
The probe is protected by an ultra-powerful heat shield that is just 4.5 inches (11.43 centimeters) thick.
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.More news: Frank Lampard reveals why Leeds United beat Derby in Championship demolition job
The probe will help scientists understand more about the nature of the sun by taking measurements of solar winds, a flow of ionised gases.
Parker Solar Probe will make its journey all the way to the Sun's atmosphere, or corona - closer to the Sun than any spacecraft in history.
The probe is equipped with a 4 1/2-inch thick carbon-carbon heat shield created to withstand temperatures of about 2,500 degrees Fahrenheit.
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.
The goal for the Parker Solar Probe is to make 24 passes through the corona during its seven-year mission.More news: Look to the Skies This Weekend for a Colorado Meteor Shower
Parker, now 91, recalled that at first some people did not believe in his theory.
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.
"It was just a matter of sitting out the deniers for four years until the Venus Mariner 2 spacecraft showed that, by golly, there was a solar wind", Parker said earlier this week. The shield took more than a decade to develop and 18 months to build.
If it launches successfully at the same time on Sunday, the probe will reach speeds of up to 430,000 miles per hour (700,000 km/h). "Each time we fly by we get closer and closer to the Sun", Driesman added.More news: Crocs to outsource manufacture while closing 132 stores
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