Night Watchmen

7/15/07 - 7/21/07
by C. Zaitz

There are a lot of things floating above us, circling the planet all day long, all night long. While we are all sleeping, there are flocks of satellites gliding silently overhead. If you’ve been out this summer even for ten minutes of star gazing, you’ve seen them. I love it when you can see more than one at a time. They look like a flotilla of space ships, and I imagine a future where they are just commuters coming to and from work.

Meanwhile I looked into what is really up there. Mostly, it’s derelict satellites, parts of old rockets, debris from collisions and even frozen space sewage. It seems the astronauts launch it out into space to get rid of it. Unfortunately, the bags of waste have the same orbit as they do, so it is not unheard of that someone might meet up with it in a future orbit.

There are many different types of orbits for satellites. The International Space Station and most of our weather satellites are in LEO’s, or low earth orbits. They are speeding along at nearly 20,000 mph because they are so “close” to earth, at only 200-500 miles. They circle the earth every 90 minutes. If they went any slower, earth’s gravity would overcome them and they would tumble to earth, burning streaks of incinerated satellite parts as they fell.

A common LEO, especially for satellites that need to see the whole earth over time, is a polar orbit. As the satellite travels from pole to pole, the earth rotates underneath. Over time, the satellite will have passed over the entire planet, just by maintaining its orbit. They can map the entire earth. Remote sensing and long term weather satellites are often in these polar orbits. These are very common to see. I saw three the other night, all at slightly different speeds, but traveling along the same trajectory like silent watchmen.

A GEO is a much higher orbit. GEOs are geosynchronous orbits, meaning they are up so high and going just the right speed so that they appear to be stationary over a certain spot on earth. You can imagine what use these orbits would be, especially if you were curious about a certain spot on earth. Unfortunately, at 22,000 miles up, the view is not as sharp as a lower orbiting satellite's. Their advantage is that they have a large coverage area. We use them for relaying a signal for communication or broadcasting. Our telecommunications satellites are in GEO orbits. The problem with this kind of orbit is that the satellite must be directly over the equator to maintain the orbit. That leaves out the polar regions, and those folks want their satellite TV, just like we do. So we have another orbit, a highly elliptical one, which can come close to earth at one point, even a polar region, and then wander father out.

If you’d like to know exactly when satellites are passing over your head, you can go to the Heavens Above website and enter your town. You’ll be surprised at what you can see. And it’s just the tip of the iceberg of the night watchmen. You’ll be surprised at who’s seeing you!

Until next week, my friends, enjoy the view.