12 Questions
What is the direction of satellite motion in a retrograde orbit?
Counter to the earth's rotation
What is the angle measured from the Υ line to the ascending node?
Right ascension of the ascending node
What is the term for the point where the orbit crosses the equatorial plane going from north to south?
Descending node
What is the term for the angle between the orbital plane and the earth's equatorial plane?
Inclination
What is the term for the average value of the angular position of the satellite with reference to the perigee?
Mean anomaly
How many orbital elements are there in the Keplerian Element Set?
6
What is the shape of the path followed by a satellite around the primary according to Kepler's first law?
Ellipse
What is the relation between the square of the periodic time of orbit and the mean distance between the two bodies according to Kepler's third law?
Proportional to the cube
What is the point where the orbit crosses the equatorial plane going from south to north?
Ascending node
What is the term for the path traced out on the earth's surface directly below the satellite?
Subsatellite path
What is the gravitational constant of the earth represented by in the Kepler's laws?
𝜇
What is the term for the line joining the perigee and apogee through the center of the earth?
Line of apsides
Study Notes
Kepler's Laws
- Satellites orbiting the Earth follow Kepler's laws, just like planets orbiting the Sun.
- Kepler's first law: a satellite's path around the primary is an ellipse.
- Kepler's second law: a satellite sweeps out equal areas in its orbital plane in equal time intervals, focused at the barycenter.
- Kepler's third law: the square of the orbital period is proportional to the cube of the mean distance between the two bodies.
Orbital Parameters
- Subsatellite path: the path traced out on the Earth's surface directly below the satellite.
- Apogee: the point farthest from the Earth, with an apogee height (ha).
- Perigee: the point of closest approach to the Earth, with a perigee height (hp).
- Line of apsides: the line joining the perigee and apogee through the center of the Earth.
- Ascending node: the point where the orbit crosses the equatorial plane going from south to north.
- Descending node: the point where the orbit crosses the equatorial plane going from north to south.
- Line of nodes: the line joining the ascending and descending nodes through the center of the Earth.
- Inclination (i): the angle between the orbital plane and the Earth's equatorial plane.
Orbit Types
- Prograde orbit: an orbit in which the satellite moves in the same direction as the Earth's rotation (also known as a direct orbit).
- Retrograde orbit: an orbit in which the satellite moves in a direction counter to the Earth's rotation.
Keplerian Element Set
- The Keplerian element set consists of six orbital elements: a, e, M0, ω, i, Ω.
- These elements define the satellite's orbit.
Orbit Perturbations
- Orbit perturbations are caused by three main factors:
- Earth's oblateness
- Equatorial ellipticity
- Atmospheric drag
Test your knowledge of satellite communications, including Kepler's laws, orbital parameters, and the effects of Earth's oblateness, equatorial ellipticity, and atmospheric drag. This quiz is based on lecture slides from a satellite communications course.
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