The Magic of GPS

Though the mountains divide,
And the oceans are wide,
It's a small world after all.
-Lyrics to It's a Small World

As I’ve commented before, my wife and I are not anti-technology, we’re just cheap. So we are late adopters of technology – waiting for the prices to come done to affordable levels. But once purchased and used for awhile, it’s hard to look back and imagine how we ever lived without it. A friend recently told us about being stuck outside her locked office without a ride home “in pre-cell phone days”. And who can imagine driving without a GPS? It’s like a magic map!

Do you know the history and workings of GPS? Well here are some interesting GPS factoids courtesy of pingdom.com

• There are always at least 24 active GPS satellites circling Earth, although today there are more than 30, including a couple of spares. Their orbits are spread out so that no matter where on Earth you are, you will have at least six of them in your line of sight.

• Each GPS satellite goes around the world once every 12 hours. The satellites travel 12,500 miles (20,000 km) above us at roughly 7,000 miles per hour (11,000 km per hour). They have small boosters so they can adjust their path when needed.

• The first full constellation of 24 satellites was completed in 1994. The first of those 24 satellites was sent up in 1989.

• To get a reliable position reading, your GPS receiver will have to combine the signals from at least four satellites, although in some special cases, three are enough.

• GPS was made public due to a tragedy. In 1983, Korean Air Lines Flight 007 entered Soviet airspace after a navigation error and was shot down, killing all 269 passengers. This incident resulted in President Ronald Reagan ordering the Unites States military to make the Global Positioning System available for civilian use once it was completed, so that similar incidents could be avoided in the future.

• NAVSTAR is the US military name for the Global Positioning System.

• GPS isn’t just for navigation. It can also be used to get a very exact time stamp. Every GPS satellite has multiple atomic clocks and the time is included in the signal it sends out. With the help of these signals, a GPS receiver can determine the current time within 100 billionths of a second. These signals are for example used to synchronize base stations in cell phone networks.

• Relativistic effects. The clocks on the satellite are subject to the effects of Einstein’s theory of relativity, running slightly slower than those on Earth. This is corrected by control signals from Earth Ground antennas spread around the world.

• The 50th Space Wing of the United States Air Force operates the GPS satellites.

• Until 2000, civilian GPS use was crippled by a feature called Selective Availability. It introduced a random error of up to 328 feet (100 meters) in the civilian signal to make GPS less useful for precision navigation. (GPS has different signals for military and civilian use.) Selective Availability was deactivated in May 1, 2000. The United States still has the ability to deactivate the civilian signal, if need be even for specific regions.

• NAVSTAR GPS isn’t the only game in town. There are several other Global Navigation Satellite Systems in existence or on their way: The European Union is working on a system called Galileo, Russia has GLONASS (completed in partnership with India), and China has plans for a system called Compass. There are also systems that offer specific regional coverage, for example Japan’s QZSS and China’s Beidou.

Bottom Line

"Any sufficiently advanced technology is indistinguishable from magic." - Arthur C. Clarke