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How do scientists put satellites into space

  1. Oct 21, 2005 #1
    How do scientists ensure that a satellite passes the same point on earth's surface over and over again in each successive revolution?

    Isn't there any variation in the latitude over which the satellite passes?
     
  2. jcsd
  3. Oct 21, 2005 #2

    russ_watters

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    Staff: Mentor

    Depends on the purpose of the satellite and the orbit. Some satellites sit stationary above the equator. Others, in low-earth-orbit, will oscillate as you suggest, but whether that's a problem depends on the purpose of the satellite. Many types of satellites (such as GPS satellites) are launched in constellations, calculated to ensure that though individual satellites might be in different places at different times, the constellation covers the entire globe.

    I'm sure enigma can provide more specifics...
     
  4. Oct 21, 2005 #3
    This site might be helpful
     
  5. Oct 21, 2005 #4

    Danger

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    Lots of surveillance satellites (military, agricultural, geological, etc.) are deliberately set to pass over a slightly different area on each orbit in order to get more coverage at the same photographic resolution. Think of it as a scanning raster, the same as the electron gun in a CRT. The cycle keeps repeating to provide a full-scale picture.
     
  6. Oct 21, 2005 #5

    tony873004

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    If you make your satellite's equatorial inclination the same as the latitude of the area you want to photograph, you'll make several similar successive passes over that area.
    Look at the ground track image below. It shows the orbits of two satellites, one with an inclination of about 55 degrees (yellow) and the other with an inclination of about 28 degrees.
    The vertical lines on the map mark longitude and are 30 degrees apart. The Earth rotates at 15 degrees per hour. So after two hours, the two lines representing the orbits will be in the same places, but the image of Earth's surface below them will have drifted to the right by one 30-degree increment.
    Notice where the Aleutian Islands of Alaska are. Take a look at the yellow orbit. Notice how it flattens out at the top of the orbit. There will be about 5 orbits in a row, starting between the 2nd & 3rd lines of longitude from the left, and ending between the 4th & 5th lines, where the Aleutian Islands are in excellent viewing position. Just make sure that your orbit's high point is on the day side of Earth if the Aleutians are what you want to take pictures of. A few hours later, you'll get 5 good Moscow photo opportunities in a row, and a few hours after that, 5 good Scotland opportunities in a row.
    You also get the same advantage in the Southern Hemisphere, but it will be the the night side of the globe if you position yourself for Northern Hemisphere daytime viewing.
    Notice the Green orbit. It's positioned nicely for 7 successive Florida flyovers. The closer to the equator you get, the more successive orbits you get. If your target is on the equator, every orbit gives you a good flyover.
     

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  7. Oct 21, 2005 #6

    Labguy

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    This site gives a pretty good explanation of both Geostationary and Geosynchronous orbits. The posts above already cover the polar and inclined orbits.
     
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