Satellite Motion

Try out these two pages for more info on this chapter's topic

CpSurf- Hewitt's Companion Web Page for this chapter
HyperPhysics - Orbit Concepts

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  • Terms

    apogee

    ellipse

    escape speed

    focus

    perigee

    period

  • 14.1 Earth Satellites

  • 14.2 Circular Orbits

    • Rotational speed of a satellite in a low circular orbit is about 4/minute so to complete one orbit takes 90 minutes. This is called the period, the time it takes to complete one orbit

    • Geo-synchronus Satellites orbit about 5.5 x Earth's radius above the equator (or 6.5 from Earth's CofM), resulting in a period of 24 hours. This results in the satellite appearing to us as being in the same spot in the sky every night. This is is how your DirecTV dish works!

    • Higher orbital speeds result in smaller periods

    • The Moon's Period is 27.5 days, that is why the moon's phases are not on the same days each month

    • Go to Hyperphysics for more info on Circular Orbits and calculators including this ORBITAL VELOCITY CALCULATOR

    • Try out this orbit simulation showing Kepler's Laws using the orbits of the Earth and Mars around the Sun, Note how the period is affected by varying the orbital radius http://jersey.uoregon.edu/vlab/kepler/kph.html


      click on thumbnail to see what it looks like

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  • 14.3 Elliptical Orbits

    • Objects just above the effects of our atmosphere will overshoot a circular orbit path if given a horizontal speed slightly greater than 8 m/s, resulting in an elliptical orbit. Go to HyperPhysics for more information on Elliptical Orbits

    • An ellipse is a closed planar path that is one form of what is called a conic section. Circles and ellipses are both forms of conic curves, a circle is simply an ellipse where the two foci are the same point, the center.

    • TRY THIS: Make a cone out of thick paper and glue or tape the edge. Flatten it and then use some scissors to make a straight slice through it at any angle. Un-flatten it back to it's original cone shape. The edge of the cut will be a planar curve called a conic section. All cuts will result in the edges of cut forming an ellipse, if you cut normal to the cone's axis , the edge will be a circle which is a special type if ellipse.,  (If you mess up and cut through one end. That makes a parabola, also a conic)

    • Try out this simulation from NASA of a satellite in an elliptical orbit, You can chage the eccenticity of the orbit and see the results. Watch out or you might crash the satellite into the Earth! http://observe.arc.nasa.gov/nasa/education/reference/orbits/orbit1.html

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  • 14.4 Escape Velocity (Speed)

    DO YOU LIKE MARSHMALLOWS? Go to this page and try out the experiment for calculating the speed of light!

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  • Summary

    • Speed of a satellite in circular orbit is not changed by gravity

    • The speed of a satellite in an elliptical orbit decreases as it recedes from the earth and increases as it approaches from the earth

    • Energy is conserved throughout an elliptical orbit

    • If something is launched from earth at a speed exceeding 11.2 km/s, or equivalently, with more than 60MJ or kinetic energy, it will escape from the Earth

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  • Links to more info

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Copyright 2005 -  S. B. EglI