# Orb.mec: Is the inclination of an ecliptic-perpendicular orbit 113,4º?

• xpell
In summary: You need to use two angles to define a direction in space, not just one.In summary, the inclination of an orbit launched perpendicular to the ecliptic plane and passing through the North and South ecliptic poles would be either 113.4º or 66.6º, depending on whether it is a retrograde orbit or not. The direction of the rocket launch is different from the final motion of the satellite due to the rotation of Earth. If the orbit is around Earth, the inclination should be between these two values. If the orbit is around the Sun, the axial tilt of Earth does not matter. The orbit can be either Earth-centric or heliocentric. The exact angle of inclination depends on the time and direction of launch
xpell
I'm trying to understand this one. Let's imagine we want to launch a satellite to the perpendicular-to-the-plane-of-the-ecliptic orbit ("passing through the North and South ecliptic poles", or perpendicular to the Sun-Earth line, through the Earth). Since the Earth's axial tilt is around 23.4º, would the inclination of this orbit (and the azimuth of the rocket launch) be 113.4º (90+23.4)? (I think so!) Or maybe would it be 66.6º (90-23.4), as I've been suggested elsewhere?

And a couple secondary questions:

1. If it is 113.4º, this is a retrograde orbit, isn't it?
2. Would this be most probably an Earth-centric orbit or an Heliocentric orbit?
3. Have you heard of any real satellite using this orbit?

Sorry for my English, it's not my primary language, hope you'll understand! Thank you in advance for your answers!

Last edited:
Inclinations larger than 90° are called retrograde orbits, right.
The direction of the rocket launch is different from the final motion of the satellite, as you always have the rotation of Earth as additional velocity.Assuming you mean an orbit around earth:

Perpendicular to the ecliptic plane is not enough to define the orbit (and with it, its inclination) in a unique way, and the sun-earth line varies within a year. Do you want your orbit to change to keep it Sun-synchronous? That orbit is used by several satellites.

The inclination should be between the two values you calculated, depending on the chosen orbit.If you mean an orbit around sun, the axial tilt of Earth does not matter as the ecliptic is defined in terms of the orbit.

A few things:
You could launch a rocket into an orbit perpendicular to the ecliptic. Its inclination to the ecliptic would be, of course, 90°. Because the Earth spins and revolves around the Sun, the launch angle is always changing. However, once in its orbit, it would more or less maintain a constant angle relative to Earth's equator and poles. The exact angle depends on exactly when and in what direction it was launched. It won't be inclined at (90°-23.4°) to the equator unless you happened to launch it such that its ascending and descending nodes (google them) match the equinoxes.

You could launch a rocket into either a geocentric or a heliocentric orbit like this. Heliocentric requires more energy, in order to escape Earth's gravity.

By the way, you probably have a bad definition for "azimuth" as it applies to this kind of problem.

## 1. What is an ecliptic-perpendicular orbit?

An ecliptic-perpendicular orbit is an orbit that is perpendicular to the plane of the ecliptic, which is the plane in which the Earth orbits around the Sun. This type of orbit is also known as a polar orbit.

## 2. How is the inclination of an orbit measured?

The inclination of an orbit is measured in degrees relative to the reference plane, which is usually the plane of the ecliptic. It represents the angle between the orbital plane and the reference plane.

## 3. Why is the inclination of an orbit important?

The inclination of an orbit is important because it affects the path of the orbiting object around the central body. It also determines the amount of sunlight the object receives and can impact its stability and ability to maintain its orbit.

## 4. How is the inclination of an orbit calculated?

The inclination of an orbit can be calculated using the orbital elements of the orbit, such as the semi-major axis, eccentricity, and argument of periapsis. These elements are used to determine the orientation of the orbit in space and the angle of inclination.

## 5. What is the significance of an orbit with an inclination of 113.4º?

An orbit with an inclination of 113.4º is considered a retrograde orbit, meaning it moves in the opposite direction of most other objects in the solar system. This type of orbit is rare and is typically found among some of the outer planets and their moons.

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