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Why are geosynchronous orbirs in equatorial plane circular?

  1. Oct 25, 2005 #1
    Anybody can answer my query ?

    thanks !
     
  2. jcsd
  3. Oct 25, 2005 #2

    russ_watters

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    Is this a homework question? Ask yourself: what are the differences between a circular and an elliptical orbit?
     
  4. Oct 25, 2005 #3
    Why? Because they are manmade.
     
  5. Oct 25, 2005 #4
    This isn't a homework problem.
    Difference between circle and ellipse is that their eccentricities are 0 and (0,1) respectively.That doesn't seem to strike anything to me or am I too dumb ??
     
  6. Oct 26, 2005 #5
    No, the difference between the two would not be zero, it would be whatever is the eccentricity of the elipse is. Circular orbits have no eccentricity, so eccentricity of elipse minus zero is eccentricity of elipse.

    Research into Arthur Clarke who was a big pusher of geosynch circular orbits as early as the 40's. He published a book in '68 called Promise of Space which explains the benefits and how this may be achieved. But do not read anything past this...be fore warned.
     
  7. Oct 26, 2005 #6

    tony873004

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    They don't have to be circular. They can have as much eccentricity as you want, as long as their period is 24 hours.

    But they are circular anyways. Like Plastic Photon said, its because they're manmade, and that's the way we want them. Otherwise, we would need motors on our satellite dishes to track them as they traced analemmas around their average positions.
     
  8. Oct 26, 2005 #7

    russ_watters

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    Well, what I was getting at is if the orbits weren't circular, they wouldn't be stationary.
     
  9. Oct 26, 2005 #8

    Janus

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    True, but the OP wasn't asking about geostationary orbits, but geosynchronous orbits. The first has to be circular and in the equatorial plane, the second doesn't. Of course, it is possible that the OP isn't aware of the difference or said one when he meant the other.
     
  10. Oct 26, 2005 #9

    Astronuc

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  11. Oct 26, 2005 #10

    russ_watters

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    Could be....like me! :redface:

    Is there much use for geosynchronous orbits as oposed to geostationary? Ie, are there applications where a little bit of back-and-forth doesn't make much difference?
     
  12. Oct 26, 2005 #11
    Geostationary orbit(s?, can there be more than one geostationary orbit?) are geosynchronous orbits in equatorial plane.So obviously I mean geostationary orbit.

    Hope I'm right
     
  13. Oct 26, 2005 #12

    tony873004

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    Since Eric Weisstein is 10x smarter than me, I don't want to say he's wrong, but I'm not sure I understand what is in the Scienceworld link for Geosynchronous Orbit ( http://scienceworld.wolfram.com/physics/GeosynchronousOrbit.html )
    Isn't a geostationary orbit a special case of a geosynchronous orbit. The wording of the article suggests not.
    Wouldn't it weave figure-eights around a point on the celestial equator, rather than the ecliptic?
    Any thoughts?
     
  14. Oct 26, 2005 #13

    pervect

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    The wikipedia suggests that you are right about at leat the first point

    http://en.wikipedia.org/wiki/Geosynchronous_orbit

    I think you're probably right about the second point too
     
  15. Nov 8, 2005 #14

    BobG

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    Geostationary orbits are a special case of geosynchronous orbits, just as a square is a special case of rectangles, and a circle is a special case of ellipses. (Wow, notice how I managed to come full circle? :biggrin: )

    Geosynchronous orbits are just as useful as geostationary orbits (within limits, of course, since you wouldn't want the satellite to disappear below the southern horizon). The difference is the expense of tracking the satellite - if the antenna has to move, it will be more expensive to build and it will require more training to operate.

    There's not going to be a big market for satellite TV if the user has to pay a lot for the antenna and has to attend a class to learn how to operate his antenna. You net a bigger profit by enduring the cost on the satellite end and widening the amount of customers you can appeal to.

    Being receivers only (for the most part), your satellite dishes still can take a little bit of play in the angle. Since no orbit could ever be truly geostationary for more than instant, that's a good thing. Every geosynchronous satellite orbit actually traces out figure-8 ground tracks - some satellites just have very, very small figure 8's.

    The Sun, Moon, planets, and non-uniform density of the Earth changes every orbit constantly and satellite operators have to make periodic orbit adjustments to keep each orbit nearly circular and nearly geostationary. The Sun's gravity will tend to pull every orbit towards matching the plane of the Earth's orbit around the Sun. The Moon's orbit, having been around for a long time, is already within 5 degrees of the plane of the ecliptic.

    Your commercial satellites used for satellite TV usually maintain inclinations of less than half a degree. The orbits are oriented so the Sun and Moon will pull the satellite's inclination towards zero until the orbit lies exactly in the equatorial plane. Then the orbit's inclination slowly increases until the upper limit is reached and the orbit is adjusted to set the cycle over again.
     
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