NASA just used Mars as a giant cosmic slingshot
The News
A spacecraft called Psyche just whipped past Mars at about 12,000 miles per hour , coming within 2,900 miles of the Red Planet — closer to Mars than New York is to Los Angeles. But it wasn't a visit. NASA was using Mars's gravity to fling Psyche faster and faster toward its real destination: a strange metal-rich asteroid in the asteroid belt. The trick gave the spacecraft a boost of about 1,000 mph — for free.
Professor Pip stood on a grassy hilltop, the afternoon sun glowing golden behind him. From his green coat pocket, he pulled out a small rubber ball tied to a long string.
"Today, my young scientists," he announced, his tail swishing in the breeze, "we are going to learn a trick that NASA just used to send a spaceship racing through outer space — without using any extra fuel."
"No fuel?!" said Asha, shielding her eyes from the sun.
"None! Watch closely." Pip held the string and began to twirl the ball above his head in a wide circle. Faster. Faster. The ball whooshed around so quickly that Leo's hat almost blew off.
"Now — what's keeping the ball from flying away?" Pip asked.
"The string!" all three kids shouted.
"Precisely! The string keeps tugging it back toward me. But here is the magic." Pip suddenly let go. WHOOSH! The ball zoomed off in a long arc across the meadow, much faster than he could have thrown it. "When I let go, the ball used all the speed I had built up — and shot away."
"That's how a sling works!" said Mia.
"Right again! In space, planets do the same thing — but with their gravity instead of a string." Pip pointed at the sky. "A NASA spaceship called Psyche flew very close to Mars. Mars is huge and zooming around the Sun. As Psyche swung past, Mars's gravity grabbed it like an invisible string, swung it around, and then — let it go in a new direction, going much faster."
"So Mars is like a really really big invisible sling?" asked Leo, eyes wide.
"Exactly right!" Pip beamed. "Scientists call it a gravity assist, or sometimes a slingshot maneuver. The spaceship steals a tiny bit of Mars's motion around the Sun, and Mars doesn't even notice. Psyche got a thousand miles-per-hour boost — completely free. No fuel burned."
"Where is it going?" asked Asha.
"To an asteroid that might be made almost entirely of metal — like the bones of a baby planet that never grew up. But the asteroid is so far away that we needed Mars's help just to get there in time."
Pip looked up at the dusky sky, where a faint sliver of moon was rising. "Somewhere up there, right now, that little spaceship is sailing along — carrying a piece of Mars's motion with it. Quietly. Steadily. For three more years, until it arrives."
He handed the string and ball to Mia. "Now you try. See how fast you can get it going — and notice, when you let go, which way it flies."
Spark a Conversation
- If you could give a spaceship a gravity-assist boost off any planet in our solar system, which one would you pick — and why?
- Pip said Mars "doesn't even notice" the boost it gave Psyche. Why do you think Mars hardly feels it?
- Why is using gravity to speed up a spacecraft better than using fuel?