Parker Solar Probe would be just 4cm away from the Sun. The reason for the delay was not immediately clear, but was called for after a gaseous helium alarm was sounded in the last moments before liftoff, officials said.
The probe will dip inside this tenuous atmosphere, sampling conditions, and getting to just 6.16 million km (3.83 million miles) from the Sun's broiling "surface".
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.
NASA has billed the mission as the first spacecraft to "touch the Sun".
"We've been inside the orbit of Mercury and done unbelievable things, but until you go and touch the sun, you can't answer these questions", Nicola Fox, mission project scientist, told CNN.
"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.
By the time Parker gets to its 22nd, 23rd and 24th orbits of the sun in 2024 and 2025, it will be even deeper into the corona and traveling at a record-breaking 430,000 mph (690,000 kilometers per hour).
Unlike many planetary exploration missions, which primarily orbit the planet itself, the Parker probe will be swooping closer and closer to the sun by way of an elliptical orbit that will include seven "gravity-assist" flybys of Venus.
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The heat shield is built to withstand radiation equivalent to up to about 500 times the Sun's radiation on Earth.
Experts say a worst-case scenario could cost up to two trillion dollars in the first year alone and take a decade to fully recover from.
No wonder scientists consider it the coolest, hottest mission under the sun, and what better day to launch to the sun than Sunday as NASA noted.
"We are ready. We have the flawless payload".
NASA's science mission chief, Thomas Zurbuchen, was thrilled not only with the launch, but Parker's presence.
The spacecraft, which will plunge into the sun's atmosphere, known as the corona, is protected by an ultra-powerful heat shield. "We have not been able to answer these questions".
Mankind's first mission to "touch" the Sun may have panned out differently had it not been for Indian-American astrophysicist Subrahmanyan Chandrasekhar, whose intervention made it possible for a research paper proposing the existence of solar wind to get published 60 years ago.
Tools on board will measure high-energy particles associated with flares and coronal mass ejections, as well as the changing magnetic field around the Sun.
"We'll also be the fastest human-made object ever, travelling around the Sun at speeds of up to 690,000km/h (430,000mph) - NY to Tokyo in under a minute".