In an unprecedented quest, the Parker Solar Probe will fly within 3.8 million miles of the sun's surface.
The first launch attempt on Saturday was postponed at the last minute due to technical problem related to a helium gas sensor on the rocket.
The probe is protected by heat shields capable of withstanding temperatures up to 2500 degrees Fahrenheit, and it will complete 24 orbits of the sun by 2025, reaching speeds up to 430,000 miles per hour.
Launching in a ball of flame that lit up the night sky, Nasa's Parker Solar Probe today set off on its seven-year odyssey to unlock the secrets of the Sun.
Image: The probe will make 24 close approaches to the sun over seven years.
Thousands of spectators turned up at the launch site on Sunday, including Eugene Parker, the 91-year-old astrophysicist the spacecraft is named after.
Scientists hope this close encounter will give them a better understanding of solar wind and geomagnetic storms that risk wreaking chaos on Earth by knocking out the power grid.
Weighing just 635 kgs, it is a relatively light spacecraft, Andy Driesman, project manager for the mission at the Johns Hopkins University Applied Physics Laboratory in the U.S., said in an earlier statement. Seven Venus flybys are planned over the seven-year mission to fine-tune the trajectory, setting up the close-in aim points.
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New Horizons is reportedly almost four billion miles from Earth, far beyond Pluto, measuring "a wall of hydrogen" where the waning of our Sun's energy is "creating a boundary where interstellar hydrogen piles up at the edge of the outward pressure caused by the solar wind's energy".
The first pass by the sun, at a distance of about 15 million miles - three times closer than any previous spacecraft - is expected in November.
NASA chief of the science mission directorate, Thomas Zurbuchen, said Parker is an "incredible hero of our scientific community".
When it nears the Sun, the probe will travel rapidly enough to go from NY to Tokyo in one minute - some 430,000 miles per hour, making it the fastest human-made object. The Parker Solar Probe is NASA's first ever named after a living person.
Parker, who first detailed the possibility of solar winds all the way back in 1958, said of the launch, "Wow, here we go!"
To reach its target, the Delta 4 Heavy and a solid-propellant upper stage had to supply enough energy to counteract Earth's 18-mile-per-second orbital velocity around the sun, allowing the spacecraft to fall into the inner solar system. That's further away than Parker but it will still need an impressive shield.
"So we're already in a region of very, very interesting coronal area", Fox said.
"I'll bet you 10 bucks it works", Parker said.