“…You gotta reach out – Reach out and touch someone…”
The last lesson showed how a geosynchronous (GEO) satellite can essentially “hover” over a particular area of the Earth. Almost as if a physical rigid connection keeps them moving together. This is because the GEO satellite’s orbit matches the speed of the Earth’s rotation, giving the satellite a clear view of a particular portion of the Earth 24 hours a day.
This orbital characteristic and view is a GEO satellite advantage, one characterized as persistence. But there is another advantage to persistence, one involving the satellite’s ground system and communications (click on this link to read more about what a ground system does and how complicated they can become).
“…Boy (Oh girl) you better communicate, Before it’s too late…”
If you remember from the Field of Regard (FOR) and Field of View (FOV) lesson, a GEO satellite’s FOR potentially contains a lot of the Earth’s surface at one go–about one third of it, more or less—primarily because of its altitude: 35,786 km (22,236 mi) above the Earth’s equator. Because of this, and the fact it will ONLY see that part of the Earth’s surface because it’s matching the Earth’s rotation, communications with the satellite’s ground system become relatively simple. For one thing, while unwise, a GEO ground system could get away with just one communications point from Earth to the satellite (a satellite ground terminal–more about those here) in the satellite’s FOR.
One satellite ground terminal is an unwise choice, because: Murphy’s Law. But could one ground system work? Yes. However, wiser and more far-seeing folks might choose at least two satellite ground terminals (one for primary operations and one for backup). Even with two ground terminals within the GEO satellite’s FOR, ground system requirements are simpler than for Low Earth Orbiting satellites. So, there’s the benefit, at least to the satellite operator, of a simpler ground system potentially lowering costs—but how is this better for you?
“…C-O-M-M-U-N-I-C-A-T-E…”
Easy, DISH TV satellites, for example, are all GEO satellites. So are Sirius/XM satellites. The persistence factor of a GEO satellite works in your favor if you are a subscriber to either one and live in North America. You actually operate a remote satellite terminal in your home or dashboard if you’re a subscriber (keep the sniggers to a minimum, other space operators!!). Your DISH TV satellite dish and home receiver are in your home to receive and interpret the data beamed to you from the GEO satellite. You can go to DISH TV’s site to learn more about their interpretation of this.
But it’s not just the fact you can receive the information in your home or car. It’s the fact you are receiving it ALL THE TIME. 24/7. Which means the broadcast centers are transmitting, communicating, to the GEO satellite ALL THE TIME (unless the satellite has a huge buffer–which is possible but unlikely). So long as either one of you are in the GEO satellite’s FOR, with no obscuration (things in the way) or attenuation (weather, such as rain, getting in the way) the satellite is always receiving and transmitting information from them to you. Sure, there are some small delays from signal transmission to reception, but all transmission are occurring in real-time.
“…Baby baby bounce it off your satellite – Yeah…”
So, persistence, then, means more than being able to see a specific portion of the Earth for 24 hours at a time–it also means communications can quickly occur between satellite, ground system and remote terminals. This communications occurs so quickly, that such transmissions are considered to be happening in real-time.
This communications advantage is why GEO satellites are useful for weather (or any other kind of) observation as well. Ground stations are in constant communications with GEO weather satellites, downloading important weather data changes almost as soon as they happen. Depending on GEO satellite capability and bandwidth limitations for transmitting data to the ground station, these weather changes can be analyzed and disseminated quickly.
It should be obvious potential disasters such as typhoons, hurricanes, volcanoes are of interest to many people. And that those same people appreciate warnings, such as this one, which can help them survive such disasters (as long as the information is out there for them to get). The fact this kind of thing happens so quickly and is almost taken for granted–what an age we live in!!
But is it all roses and wine?
The interspersed lyrics are from the B-52’s song, “Communicate.” A fun song from their appropriately titled album “Bouncing Off the Satellites.” And yes–this is a B-52 kick.
The Mad Spaceball 