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Important Facts About Ground Tracks:

1) The ground track extends as far North as it does South and the maximum latitude reached always equals the inclination of the orbit.

2) Since the shuttle orbits towards the East, its ground track moves across the map from left (West) to right (East).

Ground Tracks for a Rotating Earth

The shuttle continues to circle the Earth, returning to the same point in space after each orbit. If the Earth did not rotate, then it would also return to the same spot over the Earth after each complete orbit. However, the Earth rotates counterclockwise beneath the shuttle! We mentioned earlier that the Earth rotates at a fixed rate of 15° per hour (360° in 24 hours). So, as the shuttle makes on complete circle around the Earth in 1 1/2 hours (90 minutes), the Earth rotates 22.5° (15°/hour times 1 1/2 hours)! The figure below illustrates this concept. The shuttle begins an orbit directly over location A on the Earth (picture on the left). After 90 minutes, the shuttle completes one orbit and returns to the same point in space from where it started (picture on right). However, since the Earth rotates counterclockwise (towards the East) beneath the shuttle, after one orbit the shuttle is directly over point B at a location 22.5° to the West of point A.

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Shuttle starts directly over point A on the Earth.

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One complete orbit later, the shuttle has returned to its original point in space. But because of the Earth's rotation, it is now over point B, 22.5° to the West of point A.


7/17/96

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