Why space matters: Imaging Satellite Operations, Part 3

So, assuming you’ve been tagging along this far, now we know that a good low earth orbit (LEO) for taking pictures is around 313 miles.  But there’s another question that needs asking:  what’s the best LEO (aside from your dream date) for ensuring you will eventually get to take pictures of Earth’s ENTIRE surface ?

This question has more to do with the angle of the satellite’s orbit as it crosses the Earth’s equator (called inclination).  The closer the orbit’s angle is to being flat with the equator, the less of the Earth’s surface the satellite’s camera has the opportunity to view.

On the other hand, the more perpendicular the orbit’s inclination is to the Earth’s equator, the more chances the satellite’s camera has of taking pictures of all the Earth, eventually.  If the satellite’s orbit is perfectly perpendicular to the Earth’s equator, by the way, it’s in a polar orbit (since it’s constantly flying over the North and South Poles).

How does this work?

Pretend you’re holding an orange, and the orange represents the Earth.  Don’t be tempted to juice the orange.  Don’t think about screwdrivers!  Instead, draw a line around the orange parallel to the ground.  This line represents the equator as much as the orange represents the Earth (use your imagination!).

Take a coin (nickel, penny, whatever).  This will represent the satellite (more imagination required).  If you have to think of the coin in terms of the Millenium Falcon or Serenity, do that.

If you roll the coin, as the satellite, along the line representing the equator, the satellite never flies over any other patch of ground but the equator.  The Earth is rotating, but this doesn’t help your representative satellite see anything else.  All the satellite is doing is going faster than the Earth’s rotation (the satellite’s orbit could be completed in +/- 90 to 120 minutes depending on altitude) in the direction of the Earth’s rotation, and only traversing over the same surface of planet orange’s equator.

If you’re confused, I tried to show it (the explanation, not your confusion) in the picture.  It might help (or confuse you more).

But all is not lost!