'Ancient Indian Planes Could Travel From One Planet to Another'

[Bangalorean]

How does it matter for GPS devices? They give location and not time. Unless it screws up their orbit, I do not see why time would matter.

@Khagesh is right. Time is critical for GPS devices. Here's how GPS works, very briefly:

Your GPS device needs to connect to at least three satellites to get an accurate location. After connecting to three devices, it "listens" to the signal that is broadcast by the three satellites. In those signals, there are two critical pieces of information: a) The time which the signal was dispatched from the satellite, b) The name or identification number of the satellite.

Since these are all geostationary satellites (their position remains constant relative to the Earth because they revolve around Earth at the same speed as the rotational speed of Earth), the GPS device already "knows" where each satellite is.

With these two pieces of information (which satellite sent the signal and at what time did the satellite dispatch the signal), your GPS device can easily find out the distance between the satellite and itself. When it connects to three satellites and finds out the distance from each of those satellites to itself, its a matter of simple trigonometry to find the device's own location.

This is a beautiful and elegant solution. There is only unidirectional communication. The device does not send any information up to the satellite. At the end of the day, all the GPS device knows are your coordinates. It then overlays your coordinates on a map and that helps you know on which road you are, what is your speed, altitude, etc.

Therefore, the time component is critical in GPS devices. If the time goes wrong, your location goes wrong.

 

[Sakal Gharelu Ustad]

@Khagesh is right. Time is critical for GPS devices. Here's how GPS works, very briefly:

Your GPS device needs to connect to at least three satellites to get an accurate location. After connecting to three devices, it "listens" to the signal that is broadcast by the three satellites. In those signals, there are two critical pieces of information: a) The time which the signal was dispatched from the satellite, b) The name or identification number of the satellite.

Since these are all geostationary satellites (their position remains constant relative to the Earth because they revolve around Earth at the same speed as the rotational speed of Earth), the GPS device already "knows" where each satellite is.

With these two pieces of information (which satellite sent the signal and at what time did the satellite dispatch the signal), your GPS device can easily find out the distance between the satellite and itself. When it connects to three satellites and finds out the distance from each of those satellites to itself, its a matter of simple trigonometry to find the device's own location.

This is a beautiful and elegant solution. There is only unidirectional communication. The device does not send any information up to the satellite. At the end of the day, all the GPS device knows are your coordinates. It then overlays your coordinates on a map and that helps you know on which road you are, what is your speed, altitude, etc.


Therefore, the time component is critical in GPS devices. If the time goes wrong, your location goes wrong.

Technically speaking if the GPS device also knows the time error of the satellites it can always correct for time discrepancy.

For eg, if all the satellites loose time (given they are located symmetrically in the orbit) at same rate then the device can recalculate easily. Btw, how much time does a satellite loose in a year?