This has always been my intuition, but it's nice to see a physical demonstration.
-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Physical demonstration of a gravity assist in 2D
- Thread starter JB47394
- Start date
That is very cool...
The story of the man behind calculating the gravity assist trajectories, and the once-every-76-years planetary alignment coniceded to make the Voyager's "Grand Tour" possible is pretty interesting too...
For anybody really interested in geeking out, I have a PDF copy of NASA/JPL's "Voyager Travel Guide", a 170 type-written page in-depth treatise on the mission of Voyager... PM me if you want a copy:
The story of the man behind calculating the gravity assist trajectories, and the once-every-76-years planetary alignment coniceded to make the Voyager's "Grand Tour" possible is pretty interesting too...
For anybody really interested in geeking out, I have a PDF copy of NASA/JPL's "Voyager Travel Guide", a 170 type-written page in-depth treatise on the mission of Voyager... PM me if you want a copy:
Huh, all this time, I had assumed the gravity assist occurred because the spacecraft fired thrusters at a a particular point approaching the planet. I didn’t realize it was using the planet’s own motion to created a slingshot effect. It is a totally passive activity from the spacecraft’s point of view. That is even cooler. I guess this is how planets can be flung out of solar systems in complex situations.
CapsEngineer
Member
Ah cool thanks... the original location I had downloaded it from years ago is no longer up... hadn't seen a new one...
This is a really cool demo. All along I was thinking the increase in speed of the spacecraft due to gravity assist is primarily a function of the gravity (or mass) of the planet.
But actually it is a function of how fast the planet is orbiting the sun. The gravity just changes the direction.
Did I get that right ?
But actually it is a function of how fast the planet is orbiting the sun. The gravity just changes the direction.
Did I get that right ?
Yes, the gravity pull on the craft when incoming is canceled out by the gravity pull on the craft when outgoing, as they are forces acting on the craft in oppisite vectors as it approaches and departs.
However, the speed of the planet adds to the velocity of the craft in the same direction the whole time, hence a net gain for the craft... actual speed gain will depend on the approach/departure angle of the craft, but overall positive as long as the travel vectors of both is overall in the same direction to at least some degree...
The simplest way I can explain it is that your exit velocity from a hyperbolic pass on a planet is the same as your entrance velocity. But those velocities are measured relative to the planet. So if the planet is moving, and you can change your direction relative to the planet, then by changing your direction within in a system of planets, you are changing your velocity relative to other planets because they don't share the original planet's velocity.
The only real purpose of the sun is to keep all the planets near each other. And to complicate the heck out of gravity assists because they're moving in elliptical orbits, not straight lines.
Here's another way of thinking about it. You're skating along when you see a pretty girl skating in the opposite direction. You're going 10 mph one way and she's going 10 mph in the opposite direction. Well, there's a work vehicle following her at her speed. That means that you're going 20 mph relative to the work vehicle. As you get to it, you grab onto it and swing around it. All the while, you're going 20 mph relative to the work vehicle. That never changes. When you've swung around enough that you're going in the same direction as the pretty girl, you let go. You're still moving at 20 mph relative to the work vehicle, which was already moving at the same speed as the pretty girl. So that means that you're going 20 mph faster than the pretty girl. You zip past, crash into some bushes, she laughs and skates on by. That's gravity assists in a nutshell.
