Finding A Park For Your Satellite

Anyone who lives in a city knows how hard it is to find a good parking spot. We take this for granted.

What you probably don’t realise is that satellite parking spaces are filling fast too.

I discovered this after an interesting Saturday night. I have an alert on Twitter which lets me know when the International Space Station will be crossing over in sight of Wellington. Despite having had this service for at least six months, I have seen the ISS precisely twice. And one of those was sheer fluke.

So on Saturday I was out at Tawa having dinner with my friend Steve and his family. I thought it would be fun to take out some binoculars and watch the ISS fly over at about 6.50pm. I set an alarm on my cellphone to remind me.

It was a beautiful night; cloudless with just a hint of a breeze. The whole family (there were nine of us) piled out of the house with three minutes to spare. I pointed to the south-west and said: “It’ll be quite bright and will appear down there somewhere.”

The binoculars were passed around. The first candidate turned out to be a low-flying plane. Then somebody said: “I see it!” and pointed straight up to a bright star glinting above.

The person with the binoculars said: “Yes, it’s definitely a satellite. It’s moving a little bit and I can see it’s in two parts.”

This made sense, because at that time the ISS had a space shuttle attached. Yet I had seen the ISS before, and it was motoring. It wasn’t just sitting there.

Steve helpfully suggested: “Maybe it’s not the ISS. Maybe it’s a geostationary satellite?”

Well, that sounded logical. But then I noticed that what I first thought was a plane was in fact the ISS. Which seemed fair because I’d previously seen a plane that we thought was the ISS.

But it started me thinking: are there any geostationary satellites sitting above Wellington? Well, I investigated yesterday, and discovered that, no, there are no satellites sitting permanently over the city in which I live.

That’s because apparently a geostationary satellite can only remain effectively stationary if it is directly above the equator. It has something to do with inclination and “eccentricity”.

I’d found a list of commercial satellites in geostationary orbit dated December 2009 and it totalled 287 (an abnormal amount owned by Boeing).

Now, for a satellite to remain in geostationary orbit it must be at an altitude of 35,786km. Adding in the Earth’s diameter we’re looking at an orbiting circumference of 264,924km. So, at this point, in theory, there’s 923km available for each satellite. Which is a pretty big parking spot.

But the owners of any satellites will want to ensure it remains over a certain point of the Earth to get the best signal. This means that even though each satellite “sees” more than 40 per cent of the planet’s surface, there are an ever-decreasing number of parking spots over any particular city.

I wonder how long before somebody starts putting in parking meters up there.