Chapter 2: Orbital Aspects of Satellite Communications
16 September 2011
2.1 Orbits
we talked about satellites in inclined orbits: the Molniya satellites with their higly elliptical orbits, military satellites, and GPS satellites. We also talked about satellites in polar orbits: Tiros- N series, NOAA satellites which also provide SARSAT service.

19 September 2011
The topic is Orbital Mechanics. Important are: Kepler's laws, Newton's Universal law of Gravitation and Newton's 2nd Law of Motion. With Newton's laws we can describe the motion of a satellite. It is a motion in a plane. The position of a satellite in space at any time is given by the set of 6 Keplerian Elements, or Keplerian Orbital Elements.  NASA, for example, gives these Elements in a two-line format . Click here for examples.

21 September 2011
We tried to visualize an orbit with particular Keplerian orbital parameters by using a globe and cardboard models for the orbital plane and the orbital ellipse.  We talked about the Vernal Equinox, the zero coordinate point for the geocentric equatorial coordinate system. This coordiante system is generally used for positions of celestial sources. It is also the position through which the orientation of the orbital plane is linked to the celestial reference frame. Then we used as an example a set of Keplerian orbital parameters and properly positioned a satellite in three-dimensional space around a globe with the use of cardboard models for the orbital plane and the orbital ellipse. The motion of the satellite and its position at any given time are given by the solution of the differential equation derived from Newton's laws and the Keplerian Elements. Assignment #1 is now on the web.

23 September 2011

We practised visualizing the Keplerian orbit parameters. Then we started on the Orbit Perturbations.

26 September 2011
We talked about the effects of the equatorial bulge and looked at numerical examples.  Look at LAGEOS for a satellite of which the orbit can be determined very accurately. Look here for the latest GRACE results in the form of gravitational deviations from a geoid.

28 September 2011
We learned about effects of the equatorial ellipticity and then about third body effects on the Keplerian orbital parameters, the atmospheric drag and the solar radiation pressure. We started on the coordiante transformations.

30 September 2011
We covered most of the coordinate transformations:  perifocal coordinate system, geocentric equatorial coordinate system, topocentric horizon coordinate system. We learned about LST, GST, UT, mean sidereal and solar days.

3 October 2011
We had our third serious quiz. We also finished the coordinate transformations and then computed the look angles and the range to a satellite. We started computing the visibility of a geostationary satellite.

5 October 2011
We talked about the Nobel Prize winners in Physics of 2011. Then we finished the visibility part of the section and then
talked about Earth eclipse and sun transit outage.

7 October 2011
We talked about the launch vehicles, e.g.: Delta,  Ariane,  Proton, HV, Long March.
Look here and here for the launch of Radioastron. Then we looked at the launch orbit. That finishes Chapter 2.