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Thread: Geostationary Orbit

  1. #1

    Geostationary Orbit

    How do you get a geostationary orbit?

    From my understanding this is when a satellite orbits the earth (or Kerbin in this case) in the same position relative to the earth. Thats a horrible explanation I know. So any help or guidance on how to do this would be much appreciated!



    Douglas
    Last edited by RocketScientistsSon; 25th September 2013 at 07:49.
    "Getting old is mandatory. Growing up is optional"


  2. #2
    In order to do this, the spacecraft's angular velocity must be equal to the earth's angular velocity. The orbit at which this works for Kerbin is a circular orbit (or as close as you can get!) at 2,868.75 km above the surface of Kerbin, at a speed of 1009.0 m/s

  3. #3
    Junior Rocket Scientist Anton P. Nym's Avatar
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    A geostationary orbit is a circular (and equatorial) orbit with a period exactly the same as the length of the planet's day. On Kerbin, that's 6 hours... which you can get with a circular, equatorial orbit of 2868.75km according to the Wiki.

    Some planets don't have a geostationary orbit, as their sphere of influence isn't big enough. (Could be due to low mass, slow rotation, or close to a bigger planet.)

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  4. #4
    A GSO is simply a circular, equatorial orbit at a certain altitude, different for each body, where the orbital and rotational velocities are matched so that the same face of the body being orbited is presented to the spacecraft at all times - so if you drew an imaginary point on the surface of the body, that point would appear to always be in the same place from orbit, whatever time you looked - and similarly, from the ground, the satellite would appear to hang motionless in the sky.
    Here's a Wikipedia animation of two bodies in GSO:



    The KSP Wiki gives the altitude your spacecraft needs to be at to be in a GSO for all bodies in the game. Some bodies don't have one, though, due to the limited sphere of influence the game gives them.

  5. #5
    TL;DR 2‚ÄČ868.75 km


    You're on the right track. A Geo-Stationary Orbit is one where the time for one orbit is the same as the time for one sidereal day; 6 hours in Kerbin's case. When your orbit is at 0 degrees inclination (around the equator) then the satellite appear to stay in place with the Planet, however you cannot achieve this at any other spot than the equator. If you think about how you would stay stationary over the north or south pole, this quickly becomes obvious. Each planet is different in their geostationary position; and it depends on 2 variables the mass of the planet (and effectively the gravitational field) and how fast it rotates.

    Information on various geostationary orbits can be found on the KSP Wiki I suggest you look here in the future for any other bits of info.

  6. #6
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    So, in order to get there, you just perform a standard Hohmann transfer from your initial orbit to one with an altitude of 2868.75 km. The KSP Wiki even has an article with a table listing the required delta-v for the two burns, depending on your starting orbit.

  7. #7
    I highly recommend putting on RCS thrusters. Trying to get that exact speed without them...
    Founder and CEO of Porcine Avionics.

  8. #8
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    Quote Originally Posted by ArmchairGravy View Post
    I highly recommend putting on RCS thrusters. Trying to get that exact speed without them...
    I just learned about that last night while spending a good hour trying (and failing) to get the altitude just right with the ship's main engine. RCS thrusters are a tremendous help.

  9. #9
    Higher orbits have slower orbital speeds. Get high enough and eventually you'll reach a point where the satellite's orbital angular velocity is equal to Kerbin's rotational angular velocity.

  10. #10
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    Just go to an orbit where your surface speed is zero. Its not as tricky as it sounds the kerbal wiki (and people above) tells you already where it is, but remember you need to have a perfect 0 degree plane alignment as well, use a tiny engine for these very small adjustments, or RCS (someone suggest that already). Mechjeb can get you almost all the way there but no matter what your still going to need to do some manual orbital tuning to get as close to perfection as possible. This is going to require looking at your surface speed and providing thrust prograde, retrograde, north and south pole until it is zero, time warping a bit until the speed is not zero and repeat, be smart about it if you need to do more then a few d/v your doing it wrong.

    One thing I like about Kerstationary Orbit is that its a great place to do max speed time warps, the skymap is wizing around and yet the planet below is perfectly still!

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