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Short note on orbital parameters.

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Short note on orbital parameters.

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** Orbital parameters:**
Orbital elements are the parameters, which are helpful for describing the orbital motion of satellites.

Following are the orbital parameters:

Semi major axis

Eccentricity

Mean anomaly

Argument of perigee

Inclination

Right ascension of ascending node

*1. Semi major axis:*

- The length of semi-major axis (a) defines the size of satellite’s orbit.
- It is half of the major axis.
- This runs from the center through a focus to the edge of the ellipse.
- So, it is the radius of an orbit at the orbit's two most distant points.

*2. Eccentricity:*

- The value of Eccentricity (e) fixes the shape of satellite’s orbit.
- This parameter indicates the deviation of the orbit’s shape from a perfect circle.
- If the lengths of semi major axis and semi minor axis of an elliptical orbit are a & b, then the mathematical expression for eccentricity (e) will be:

*3. Mean anomaly:*

- For a satellite, the point which is closest from the Earth is known as Perigee.
- Mean anomaly (M) gives the average value of the angular position of the satellite with reference to perigee.

*4. Argument of perigee:*

- Satellite orbit cuts the equatorial plane at two points. First point is called as descending node, where the satellite passes from the northern hemisphere to the southern hemisphere.
- Second point is called as ascending node, where the satellite passes from the southern hemisphere to the northern hemisphere.
- Argument of perigee (ω) is the angle between ascending node and perigee.
- Argument of perigee is measured in the orbital plane at earth’s center in the direction of satellite motion.

*5. Inclination:*

- The angle between orbital plane and earth’s equatorial plane is known as inclination (i).
- It is measured at the ascending node with direction being east to north.
- So, inclination defines the orientation of the orbit by considering the equator of earth as reference.
- There are four types of orbits based on the angle of inclination:
- Equatorial orbit
- Polar orbit
- Prograde orbit
- Retrograde orbit

*6. Right ascension of ascending node:*

- We know that ascending node is the point, where the satellite crosses the equatorial plane while going from the southern hemisphere to the northern hemisphere.
- Right Ascension of ascending node (Ω) is the angle between line of Aries and ascending node towards east direction in equatorial plane. Aries is also called as vernal and equinox.

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