# Slingshot Effect

This isn’t a car question, it’s rocket science! Here it is. When NASA sends a spacecraft to the far reaches of the solar system, it often steers it to have a close encounter with a planet. It supposedly accelerates toward the planet, zips by, getting a boost in velocity without having to apply power. The “slingshot effect”. How can this be? Applying the laws of energy convervation, where does this extra speed come from? Shouldn’t he gravity of the planet acting on the craft slow it down after it flies by in the same amount it accelerated the craft on its approach? The spacecraft always exits at a different angle; is that a factor?

Gravity. The gravity of the spinning surface of the planet can pull the spacecraft along with it and accelerate it if it gets close enough…and the surface of the planet is traveling faster than the spacecraft.

The speed of the surface of the planet is both that speed from its spin combined with the speed of the entire sphere as it’s moving through space in its orbit around its sun. That can be many thousands of miles per hour.

The energy comes from the planet. It is slowed down ever so slightly by the encounter with the spacecraft. Yes, the angles are very important.

You can personally accomplish the same effect with a bicycle or pair of skates.

Go into a turn fairly slowly, and lean over hard into the turn while turning sharply, getting as low as you dare. You’ll experience a noticeable increase in speed, even as you straighten back up.

Thanks texases. The website and its links explained it perfectly.

You exit the slingshot at the same speed in which you entered it. The slingshot only provides more speed while you are next to the planet.

Well, now we know who slept through those physics classes!

Whitey, let me suggest you visit Texases’ link describing the effect of gravity from a spinning and moving planet on a passing body. It’s a great link.

Heck, I made A’s in HS and college physics (in the 1960s), but never learned this stuff! You mean astrophysics class?

Hey Ed,

First, I didn’t name names. I was referring to some of the replies, not your inquiry. Second, the slingshot effect is plain old Newtonian physics, nothing too fancy.

It says “…its ingoing and outgoing speeds are the same as it enters and leaves the gravity…” I guess that only holds true in relation to the planet. So is the whole premise of the slingshot effect dependent on the planet moving in the same direction you are going in relation to the sun?

Actually, it has more to do with the direction the planet is traveling relative to the direction of the spacecraft. When both are traveling the same direction, the gravity of the planet pulls the spacecraft along with the planet adding velocity. The spacecraft’s trajectory is critical, because if it enters at too direct an angle it’ll get pulled into the planet, or possibly even into orbit around the planet, and if the trajectory is too little it’ll lose the benefit of the gravitational pull.

Not! Gravity does not “spin” and the spacecraft never touches the planet…