How is a retrograde orbit possible?

Question

I need a precise answer, with as much physics involved as possible.
Signed,
An average Joe.

Answer 1

A retrograde orbit is just one that goes the other way around. The other way from what? From the usual way. What is the usual way? For artificial satellites, it is the same way the Earth rotates, or from west to east. You could launch a satellite into a retrograde orbit by sending it west from the launch pad instead of east. That is pretty much never done since the Earth's rotation gives a little boost to the rocket going east and our poor little rockets need all the help they can get.

The usual way for planets orbiting the Sun in the same direction as Earth. All the planets and most of the moons of those planets orbit the same way. This is because the nebula from which the solar system was formed was rotating in that direction and that angular momentum is still there. A few small moons of outer planets are orbiting the other way. We assume that they are really asteroids that got captured by the planets in question, and it is possible that gravity assist like maneuvers could have caused them to be captured in a backward direction.

Answer 2

Ok first let me explain a regular orbit. An orbit is attained by remaining in a continuous state of free-fall around the planet. Even though it may seem like a person in orbit is moving forward, they are really falling down towards the planet. But because they are moving so fast forward they "fall beyond the horizon". Their downward force is matched by the upward force they are attaining by "slipping" around the planet.

Now, a retrograde orbit is possible when the upward force is less than the force of gravity. A retrograde orbit cannot be sustained for long periods of time because gravity will overcome the upward force and pull you into the planet's atmosphere.

Usually retrograde orbits are performed to reduce altitude or to perform a re-entry procedure.
Hope that helps.

Answer 3

campbelp2002's answer is right. The last two paragraphs of broxolm's answer are wrong.