1 00:00:00,030 --> 00:00:04,040 NASA's Parker Solar Probe will soon fly closer 2 00:00:04,040 --> 00:00:08,160 to the Sun than any spacecraft before it-about 4 million 3 00:00:08,160 --> 00:00:12,270 miles from the visible surface. But getting that close to the Sun 4 00:00:12,270 --> 00:00:16,370 requires some fancy orbital mechanics. It takes 55 times 5 00:00:16,370 --> 00:00:20,480 more energy to go to the Sun than it does to go to Mars. 6 00:00:20,480 --> 00:00:24,600 Why is it so hard to get to the Sun? The answer is related to why 7 00:00:24,600 --> 00:00:28,690 Earth doesn't just fall straight into the Sun, despite the strong gravitational 8 00:00:28,690 --> 00:00:32,790 attraction. Earth, and everything on it, is traveling very 9 00:00:32,790 --> 00:00:36,810 fast-about 67,000 miles per hour-in a direction that is 10 00:00:36,810 --> 00:00:40,880 basically always sideways relative to the Sun. If you launch a 11 00:00:40,880 --> 00:00:45,010 rocket from Earth, straight toward the Sun, it won't lose that sideways speed, 12 00:00:45,010 --> 00:00:49,140 and so it will miss the Sun. The only way to get the rocket 13 00:00:49,140 --> 00:00:53,300 to go right into the Sun is to cancel all that sideways motion. Leave 14 00:00:53,300 --> 00:00:57,430 even a little bit and it will miss the Sun and enter a new orbit. 15 00:00:57,430 --> 00:01:01,560 To cancel Earth's motion, you have to launch the spacecraft backward as fast as Earth 16 00:01:01,560 --> 00:01:05,710 is hurtling forward. But 67,000 miles an hour is really 17 00:01:05,710 --> 00:01:09,870 fast. Spacecraft have to go upward at only 25,000 miles 18 00:01:09,870 --> 00:01:13,980 an hour to escape Earth. Getting to Mars only requires a bit 19 00:01:13,980 --> 00:01:18,100 more speed: 29,000 miles an hour. New Horizons, 20 00:01:18,100 --> 00:01:22,180 which NASA sent rushing out to Pluto, managed 36,000 miles 21 00:01:22,180 --> 00:01:26,280 per hour, or a little more than half what it would have to hit the Sun 22 00:01:26,280 --> 00:01:30,430 instead. Since Parker Solar Probe plans to fly past the Sun, 23 00:01:30,430 --> 00:01:34,600 it doesn't need to cancel out all of Earth's sideways speed, but it does need to remove 24 00:01:34,600 --> 00:01:38,690 53,000 miles per hour of it. That's why it's using one of the most 25 00:01:38,690 --> 00:01:42,880 powerful rockets available and additional gravity assists from Venus 26 00:01:42,880 --> 00:01:46,970 over a period of several years. In this case, rather than speeding up 27 00:01:46,970 --> 00:01:51,070 the spacecraft as in a typical gravity assist, Venus slows down its 28 00:01:51,070 --> 00:01:55,090 sideways motion, so the spacecraft can get close to the Sun. 29 00:01:55,090 --> 00:01:59,180 When it finally does make its closest approach to the Sun, Parker Solar Probe 30 00:01:59,180 --> 00:02:03,200 will have lost much of its sideways speed, but gained a great deal of overall 31 00:02:03,200 --> 00:02:07,310 speed, thanks to the Sun's gravity. Parker Solar Probe will hurtle 32 00:02:07,310 --> 00:02:11,470 past the Sun at 430,000 miles an hour- 33 00:02:11,470 --> 00:02:15,660 the very first human-made object to get that close. 34 00:02:15,660 --> 00:02:19,750 [Beeping] 35 00:02:19,750 --> 00:02:23,777 [Beeping]