In Orbit You Have to Slow Down to Speed Up

If you see sci-fi movies, you’d think that flying a spaceship is a bit like driving a complicated car (or a Winnebago spaceball) and George Lucas gave us Those are galactic wars With pilots who look like they’re flying fighter jets on Earth.

Good, bad news: Space is really, really different. In particular, moving a vehicle into orbit around the Earth is more complicated than that. The maneuvers you can do with the plane sometimes have the opposite effect on the orbit.

To see what I mean, we’ll first grab some basic physics and build ourselves a little model of orbital mechanics, and then I have some cool simulations of an attempted docking strategy. Read on!

circular orbit

Imagine flying in a circular orbit around the Earth. We have three major physics concepts to understand this kind of motion. first, centripetal acceleration. Remember that acceleration is a measure of how fast an object’s velocity is changing.

But velocity is not just speed, it is a specific speed direction-In other words, it is a vector. If an object is moving in a circle, its direction is constantly changing, which means it is constantly accelerating, even if its speed is constant!

The direction of this acceleration is towards the center of the circle. (“centripetal” means center-point.) The magnitude of the acceleration depends on both magnitudes of the velocity (v)(i.e., speed) and radius (rcircle This gives the following equation:

Courtesy of Rhett Allen