NASA's Parker Solar Probe just flew over 500 times the speed of sound

A fortified NASA spacecrafthas reached nearly 400,000 mph — again.

That's the fastest a human-built machine has ever flown. And it will keep picking up speed.

The U.S. spaceagency recently announced its Parker Solar Probe — the first mission to fly through the sun's outer atmosphere, or corona— matched its own speed record of 394,736 mph (635,266 kilometers per hour) during its 20th close solar approach on June 29.

Objects often accrue speed when they pass by gravitationally-powerful objects, like the sun. And in the emptiness of space, little can stop this craft from continually going faster.

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"Once it's going, it's going," Nour Raouafi, an astrophysicist at the Johns Hopkins Applied Physics Laboratory and project scientist for the mission, previously told Mashable.

SEE ALSO: NASA scientist viewed first Voyager images. What he saw gave him chills.

(At times, some minimal slowing occurs when the probe strategically passes by Venusfor "gravity assists" that propel it closer to the sun; these Venusian flybys slightly temper the craft's momentum, but ultimately result in it picking up even more speed as it zips nearer to our massive star.)

"Once it's going, it's going."

Later this year, after the probe's final Venus assist, the craft will reach a whopping 430,000 mph. At that speed, you could travel from San Francisco to Washington, D.C., in 20 seconds.

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The green line in this graphic shows the Parker Solar Probe’s 20th orbit around the sun, bringing it some 4.51 million miles from our star. Credit: NASA / Johns Hopkins APL / Steve Gribben

While traveling at such a blistering speed — over 500 times the sound barrier of some 760 mph — the NASA probe will come 3.8 million miles from the sun's surface, breaking another record. But it's well equipped for the torrid solar environs. Engineers built the Parker probe with a 4.5-inch-thick carbon heat shield that's pointed at the sun. The shield itself heats up to some 2,500 degrees Fahrenheit, but just a couple of feet behind, the environs are surprisingly pleasant. "Most of the instruments are working at room temperatures," Raouafi said.

The unprecedented endeavor into the sun's atmosphere isn't just breaking records. Scientists plan to use the incoming observations to understand how extreme space weather, caused by different types of solar explosions, can behave and ultimately impact Earth. Our fickle star, for example, can eject masses of super hot gas (plasma), called coronal mass ejections, or CMEs, at Earth. These events can wreak havoc on our power grids and communication networks — historically they've melted transformers and triggered electrical failures that trapped unsuspecting people in elevators.