One of these things is just like the other…
In an earlier post regarding the United States Air Force replacement of their Defense Support Program satellites with Space Based Infrared ones, there was a question posed to you: What do both the Space Based Infrared System (SBIRS) and Defense Support Program (DSP) satellites have in common, aside from the infrared sensor payload?
You could’ve said they are both operated by the Air Force and you wouldn’t have been wrong. But the answer (the “right” one ;-)) sought after was this: they are both satellites in a geosynchronous orbit (GEO). This orbit, if you believe Wikipedia as a reliable source, is 26,199 miles from the Earth’s center. It’s a rather special orbit and one, whether you know it or not, you rely on every day.
…One of these things is not the same…
A comparison and reminder is in order, though. Remember the Low Earth Orbit (LEO) and why some organizations use satellites in that orbit? There’s more about LEO in these lessons. A short summary of those lessons follows. The LEO satellite is closer to the Earth than the GEO—much closer: 99 to 1200 miles from the Earth’s surface. So, let’s do the old “driving a car on the freeway” comparison again: if you’re in a car on a freeway, and the car in front of you is close. So close, you not only can make out the plate registration number, but the fact the numbers are raised, dirt specks, etc. That’s what a LEO satellite gives you: an extremely good, detailed “view.” But it doesn’t give you much more than the number because you are so close. You might not see the make of the car, the color of the car, brake lights, etc.
That’s where a geosynchronous satellite comes in. If you’ve watched the evening news weather report, then chances are good you’ve seen what a GEO weather satellite can do. It shows you the bigger picture (depending on how the satellite’s image sensor payload is designed). Just like the infrared Geostationary Operational Environmental Satellites’ (GOES) image below:
Do you see how the entire “disk” of the Earth is in view of the GOES image sensor? Unlike the LEO satellites, GOES just takes one picture—and suddenly the whole of the Earth can be seen. LEO satellites need to go around the Earth multiple times to get the same image (almost).
Just this fact alone is advantageous to whoever is operating the GEO satellite (in this case, the National Oceanic and Atmospheric’s National Environmental Satellite, Data, and Information Service). And this time, we will not be covering only imagery satellites, but a few other ones hanging out in GEO, too. Stay tuned for the next few lessons…
- First of New Generation of U.S. Missile Detection Satellites Now Operational in Space (matthewaid.com)
- GSAT-7 satellite placed in geosynchronous orbit (dnaindia.com)
- India’s GSAT-7 satellite placed in geosynchronous orbit (rediff.com)
- Space X appears to pass major test of rocket technology (computerworld.co.nz)
- SpaceX successfully launches its first attempt at geosynchronous orbit (arstechnica.com)