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Sun-synchronous orbit

Another way to visualise sun-synchronous orbits

July 27, 2016

Yesterday we had a look at the orbits of imaging satellite’s from the perspective of a stationary earth. Today we are having a look at the same orbits but showing how the orbit is actually a circle with the earth rotating inside it.

We found a model of Landsat 7 on the sketchup 3D warehouse and have created a tour showing what Landsat 7’s orbit looks like. The satellite is not shown to scale but the orbit should be approximately correct. Landsat 7 crosses the equator from north to south at about 10:00 am every 98.83 minutes (yes, it’s confusing). Its orbit covers the entire earth every 16 days and then repeats.

One problem we have encountered is animating a model across the antimeridian does not work correctly in Google Earth. We have not yet found a work-around. You will notice the model appears to jump occasionally when crossing the antimeridian. Another bug is that the background of stars shakes around when playing the tour. The stars should be stationary relative to the view, as the satellite’s orbit is nearly stable with respect to the stars, drifting approximately 1 degree per day (360 degrees per year).

Here we see Landsat 7’s orbit over the course of 24 hours:

You can view it in Google Earth with this KML file. For best results turn on sunlight (the icon with a rising sun on the toolbar). We also include in the KML the orbit for 24 hours or for the full 16 days.

Note that Landsat 8 shares the same orbit but with an 8 day offset.

This is what its 16 day orbit looks like relative to the earth:

We couldn’t record the full 16 day orbit as a tour as Google Earth couldn’t handle it. We believe it is possible to use a KML feature called a Track to improve performance, but we have not yet figured out how to do that.

For comparison, here is the layout of imagery tiles that are captured by Landsat 7 as provided by the USGS:

Filed Under: Site News Tagged With: landsat, Sun-synchronous orbit

Sun-synchronous orbits with Google Earth

July 26, 2016

After our recent posts on rainbow plane offsets and the list of imaging satellites we thought it would be interesting to see what a sun-synchronous orbit actually looks like in Google Earth. We have previously written a post about sun-synchronous orbits and why most imaging satellites use them, but we only showed an approximate single orbit of the earth assuming the earth was not rotating. In reality, the earth rotates on its axis as well as going around the sun. A sun synchronous orbit is designed to drift slowly so as to keep in sync with the earth’s orbit around the sun. All this starts to get complicated when you want to plot an actual orbit. But we believe we have succeeded.


What the orbit of WorldView-3 looks like.

We used the equations from Wikipedia, which allow us to use the altitude and period of a given satellite to work out its orbit. For simplicity we start at latitude zero and longitude zero. We show the orbit for a period of approximately 24 hours. Some satellites, such as Landsat 8, have their orbits arranged so that they repeat the same path on a regular basis. Others do not.

All sun-synchronous orbits look very similar, with the differences in altitude being hardly noticeable. The most obvious difference is in the period, which affects the spacing of the orbits.


Red: Landsat 8 orbit. White: WorldView-3 orbit.

WorldView-3 has an altitude of 617 km and a period of 97 minutes.
Landsat 8 has an altitude of 703 km and a period of 98.8 minutes.

The diagonals from the north east to south west ( / ) are on the daylight side of the earth and the diagonals from south east to north west ( \ ) are on the night side.

To see the above orbits in Google Earth download this KML file. Alternatively, you can create your own orbit by entering the altitude and period below:


Sun-synchronous orbit creator.

Altitude: km

Period: minutes

Filed Under: Site News Tagged With: Sun-synchronous orbit



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