Is it a bird? Is it a Plane? No it’s a multi-million dollar piece of hardware and software travelling at about 9,000mph miles per hour in orbit around our planet!
We’ve discussed n previous blog posts the ability to utilize the many features of LiGO software such as ‘real-time tracking’ and other GPS related functions. The science of GPS play’s a crucial role in the products and services we offer but like most of humanity’s greatest scientific achievements the mechanisms of how it actually works often goes unnoticed and unappreciated. the ability hop on our smart phones and figure out exactly where we are located on the earth might have seemed like magic to even a reasonable citizen of the early 20th century. As Arthur C Clarke the famous science fiction writer noted “Any sufficiently advanced technology is indistinguishable from magic.”. Its silly to imagine that I could boil the science of how satelites, GPS’s, and smart devices work into a single pageblog post but I’d like to shed light on one of the aspects of these systems.
Each satellite in the GPS constellation orbits the earth at an altitude of about 20,000km (12427mi) from the ground, and has an orbital speed of about 14,000kph (8699mph). When taken into consideration, we can say that satellites are moving relatively faster than objects on the surface of the earth like car’s, or a person. As a result of this, the theory of special relativity suggests that the on-board satellite clocks should lag by about 7 microseconds per day due to the time dilation as a result of their relatively faster motion through space.
General relativity however, predicts that a clock that is closer to massive objects (in this case individuals on the ground being closer to earth) will apparently tick slower than clocks farther away. This amounts to on-board satellite clocks being ahead by about 45 microseconds per day. I know… I know, what the heck does that even mean right?
The outcome of these separate relative effects means that clocks on-board each satellite should tick faster than identical clocks on the ground by about 38 microseconds per day (45-7=38). 38 microseconds might not sound like much, but if you consider the fact that GPS systems run at the level of accuracy of nanoseconds, and that 38 microseconds is the equivalent of 38,000 nanoseconds, then you start to realize. If these factors weren’t taken into account errors in global positioning would begin to accumulate only after 2 minutes and would continue at a rate of about 10 kilometers (6.2 miles) a day as opposed to the 5-10-meter average accuracy we are capable of currently.
wrapping our minds around these observations can be mind-numbing, dizzying, and quite frankly detour anyone from wanting to know more about the subject. thankfully generations of dedicated physicists, mechanical engineers, and numerous other scientific fields of study have propelled these technologies to where they are today.