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NASA's Parker Solar Probe will soon fly closer

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to the Sun than any spacecraft before it-about 4 million

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miles from the visible surface. But getting that close to the Sun

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requires some fancy orbital mechanics. It takes 55 times

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more energy to go to the Sun than it does to go to Mars.

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Why is it so hard to get to the Sun? The answer is related to why

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Earth doesn't just fall straight into the Sun, despite the strong gravitational

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attraction. Earth, and everything on it, is traveling very

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fast-about 67,000 miles per hour-in a direction that is

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basically always sideways relative to the Sun. If you launch a

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rocket from Earth, straight toward the Sun, it won't lose that sideways speed,

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and so it will miss the Sun. The only way to get the rocket

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to go right into the Sun is to cancel all that sideways motion. Leave 

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even a little bit and it will miss the Sun and enter a new orbit.

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To cancel Earth's motion, you have to launch the spacecraft backward as fast as Earth

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is hurtling forward. But 67,000 miles an hour is really

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fast. Spacecraft have to go upward at only 25,000 miles

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an hour to escape Earth. Getting to Mars only requires a bit

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more speed: 29,000 miles an hour. New Horizons, 

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which NASA sent rushing out to Pluto, managed 36,000 miles

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per hour, or a little more than half what it would have to hit the Sun

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instead. Since Parker Solar Probe plans to fly past the Sun, 

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it doesn't need to cancel out all of Earth's sideways speed, but it does need to remove

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53,000 miles per hour of it. That's why it's using one of the most 

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powerful rockets available and additional gravity assists from Venus

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over a period of several years. In this case, rather than speeding up

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the spacecraft as in a typical gravity assist, Venus slows down its 

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sideways motion, so the spacecraft can get close to the Sun.

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When it finally does make its closest approach to the Sun, Parker Solar Probe

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will have lost much of its sideways speed, but gained a great deal of overall

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speed, thanks to the Sun's gravity. Parker Solar Probe will hurtle

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past the Sun at 430,000 miles an hour-

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the very first human-made object to get that close.

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[Beeping]

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[Beeping]