It's fifty times faster than a speeding bullet.

At 3:21 p.m. (EDT), NASA'S Juno Mission spacecraft will slingshot around Earth towards Jupiter, accelerating to 25 miles per second along the way and becoming the fastest man-made object in history. A .50-caliber bullet travels at about half a mile a second, by contrast -- nowhere near the blistering speed of Juno.

"The mission is very exciting," University of Iowa research scientist Bill Kurth told FoxNews.com. "We’ll come the closest we've ever come to Jupiter, within just a few thousand miles of the planet's cloud tops."

When the $1.1 billion mission launched in August 2011, scientists first attempted the brute force technique: relying on the Atlas V rocket, one of the most powerful in the world, to simply hurl the spaceship towards the distant gas giant. But Atlas wouldn't have given Juno enough juice to reach Jupiter, Kurth said.

Instead the team turned to the slingshot technique, where Earth's gravity gives the spacecraft a key speed boost.

"Juno will be really smoking as it passes Earth at a speed of about 25 miles per second relative to the Sun," said Kurth. "The primary goal is to be on our way to Jupiter, and I have every confidence we're on target that the flyby will go off without a hitch."

By harnessing the Earth's gravity, Juno will exceed the 165,000 mph it needs to reach Jupiter.

'Juno will be really smoking as it passes Earth at a speed of about 25 miles per second relative to the Sun.' — Bill Kurth, research scientist at the University of Iowa

"This is called a slingshot maneuver or gravity assist," Kurth explained. "It uses Earth's orbital motion to accelerate the spacecraft towards Jupiter." The spacecraft is expected to come within 350 miles of Earth today.

Kurth and the other scientists involved hope to learn more about the evolution of the solar system by studying Jupiter, the largest planet.

"By understanding the origins of Jupiter we learn more about other planets," he said.

Data collected from the Juno spacecraft will help scientists map the planet's magnetic and gravity fields to help them learn more about its deep interior.

"Jupiter has the brightest auroras in the solar system and this will allow us to study their processes," explained Kurth.

Among those watching is Bill Nye the Science Guy.

"Juno is a remarkable mission that everyone on Earth can learn about," Nye said in a press release. "It's part of a quest to learn how our Solar Sytem came to be and you and I got here."

Nye is hosting an eight part YouTube series called "Why with Nye" on THINKR to commemorate the event.