Location's on our mind today. There are currently 24 satellites that make up our Global Positioning System. The most recently launched, the GPS IIF SV-1, is part of a new series that offer a whole bundle of upgrades.
The GPS satellites have traditionally been launched in blocks. The first block (with a truly original name like Block I) was an experimental group of 11 satellites, the first of which launched in 1978. GPS IIF SV-1 is part of Block IIF, the fourth generation of GPS satellites. At 1600kg and with a height of 2.4m, SV-1 is the only one of its kind up there right now, but its 11 siblings are expected to join it eventually.
So, what's new? Well, for starters, the Block IIF group will be two times more accurate than the current satellites. This is good news for the FAA and military, as this increased accuracy means better tracking of aircraft. As far as John Q Yelper. is concerned though, these new models will reduce (increase?) the estimated accuracy from 6m down to two or three. (Keep in mind your signal may still be intentionally altered for national security reasons.) The boosted signal also means that you may start seeing applications that take advantage of augmented reality indoors. Just what you wanted: The ability to download and follow a mall map to American Apparel, led by a naked, furry Dov Charney.
Part of what makes Block IIF such a step up is the implementation of advanced atomic clocks, which must keep time to within 8 nanoseconds a day. To know why these very accurate clocks make a difference, you need to have a basic understanding of how GPS works. Each satellite broadcasts a signal that gives its position and the time. A GPS receiver (on Earth [in your phone] ) obtains this signal uses the difference between the two times (from the satellite and receiver) to calculate its distance from the satellite, thereby calculating its physical location on Earth.
Here's an example:
(Light travels at 186,000 miles per second: if the satellite time happened to be, for example, one-thousandth of a second behind the GPS receiver's time, then the receiver would calculate that it was 186 miles from that satellite.) By checking its time against the time of three satellites whose positions are known, a receiver could pinpoint its longitude, latitude, and altitude.
It's easy to take these upgrades for granted, so let me remember that these satellites are in OUTER SPACE, orbiting the Earth from almost 21,000km away.
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