Satellite’s ground track is the path on the surface of the Earth, which lies exactly below its orbit. Aries is also called as vernal and equinox. Right Ascension of ascending node (Ω) is the angle between line of Aries and ascending node towards east direction in equatorial plane. 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. Retrograde orbit − Angle of inclination lies between 90 and 180 degrees. Prograde orbit − Angle of inclination lies between zero and 90 degrees. Polar orbit − Angle of inclination is 90 degrees. There are four types of orbits based on the angle of inclination.Įquatorial orbit − Angle of inclination is either zero degrees or 180 degrees. So, inclination defines the orientation of the orbit by considering the equator of earth as reference. It is measured at the ascending node with direction being east to north. The angle between orbital plane and earth’s equatorial plane is known as inclination (i). If both perigee and ascending node are existing at same point, then the argument of perigee will be zero degreesĪrgument of perigee is measured in the orbital plane at earth’s center in the direction of satellite motion. Second point is called as ascending node, where the satellite passes from the southern hemisphere to the northern hemisphere.Īrgument of perigee (ω) is the angle between ascending node and perigee. First point is called as descending node, where the satellite passes from the northern hemisphere to the southern hemisphere. Satellite orbit cuts the equatorial plane at two points. At that time, Mean anomaly is used as an intermediate step. But, if the orbit is elliptical, then calculation of exact position is very difficult. If the orbit is circular, then Mean anomaly gives the angular position of the satellite in the orbit. Mean anomaly (M) gives the average value of the angular position of the satellite with reference to perigee. Mean Anomalyįor a satellite, the point which is closest from the Earth is known as Perigee. And, the remaining three satellite orbits are of elliptical corresponding to the eccentricity (e) values 0.5, 0.75 and 0.9. In above figure, the satellite orbit corresponding to eccentricity (e) value of zero is a circular orbit. The following figure shows the various satellite orbits for different eccentricity (e) values Whereas, the value of eccentricity of an elliptical orbit lies between zero and one. The value of eccentricity of a circular orbit is zero, since both a & b are equal. 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 This parameter indicates the deviation of the orbit’s shape from a perfect circle. The value of Eccentricity (e) fixes the shape of satellite’s orbit. If circular orbit is considered as a special case, then the length of semi-major axis will be equal to radius of that circular orbit. Length of semi major axis (a) not only determines the size of satellite’s orbit, but also the time period of revolution. So, it is the radius of an orbit at the orbit's two most distant points.īoth semi major axis and semi minor axis are represented in above figure. This runs from the center through a focus to the edge of the ellipse. The length of Semi-major axis (a) defines the size of satellite’s orbit. Therefore, it is easy to discriminate one satellite from other satellites based on the values of orbital elements. The above six orbital elements define the orbit of earth satellites. Orbital elements are the parameters, which are helpful for describing the orbital motion of satellites. So, we can easily understand the space operations with the knowledge of orbital motion. Orbital mechanics is the study of the motion of the satellites that are present in orbits. This path can be represented with mathematical notations.
We know that the path of satellite revolving around the earth is known as orbit.
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