Okay, you’re holding the orange in your hand again (I hope you haven’t been holding it all this time—it’s been a few days). Again, there’s a line drawn around the orange that is parallel to the ground. The line represents…(you should be thinking the words “the Earth’s equator”).
Now, roll the coin perpendicular to the line. Note that coin will cross the equator twice per orbit—once going up towards the North Pole, and once going down towards the South Pole. Assuming the coin is in a very stable orbit, it will do little else. The coin will stay in that same orbit as long as there are no other influences, taking the same path over, and over, and over again.
And the orbit itself is very quick, about 90 minutes per revolution since we’re assuming it is 313 miles from the Earth’s surface. This means the satellite coin completes about 16 orbits every 24 hours (1440 minutes/90 minutes=16). Of course, the satellite was doing this in the equatorial orbit too.
So how is this better than the equatorial orbit?
Well, the orange (Earth) rotates. So, try turning the orange, keeping the equatorial line parallel with the ground. Now, as the orange is turning, try moving the coin perpendicular to the equatorial line, and around the top of the orange, dipping down south behind the orange until it comes into your view around the bottom of the orange. Keep the coin’s south to north movement always directly in front of you. Use the picture to help guide you if I’ve successfully confused you again.
So even though the coin is following the same orbital track, you can see the surface beneath the path is moving. And because you have the coin traversing from South to North Pole and back down South again, its camera will eventually be able to take pictures of the whole world. And that’s just one satellite in one orbit…
In the previous post, I explained why a polar orbiting LEO satellite is ideal for getting pictures of the entire surface of the Earth. But one satellite takes a while to do this.
- New Explorer Mission Chooses the ‘Just-Right’ Orbit (spacedaily.com)