How do GPS work?

ElRazur · 29 Aug 2006 at 15:02

Okay i have a fair understanding of how it (receiver) locks on to the GPS satelites in sky so to speak but i have the following questions-

how does it now what direction one is facing when driving?

can anyone shed any light on how it is used to guide a missle to it target as there is no road or obstacle in the missile path? Also when a missiles locks on to a moving target is the gps responsible for this or the heat signature...?

Do all ICBM have built in gps receivers?

what will be the main differences/advantage between the new european satelite being put together at the moment over the GPS?

Thanks.

taliesyn · 29 Aug 2006 at 15:04

Look here for an excellent reference

basmic · 29 Aug 2006 at 15:06

I believe GPS positioning is done using triangulisation (sp?) - although I could be wrong.

Luke · 29 Aug 2006 at 15:11

ElRazur said:
how does it now what direction one is facing when driving?

This is the only bit I think I know.

It doesn't. Switch on satnav whilst stationary and it doesn't know which way you are facing. It's only when you move that it assumes that the direction you are travelling in is forward. You can fool it by reversing as it will rotate the map as if you were facing the other way.

Spacky · 29 Aug 2006 at 15:13

Not so if you are using hand held ones for walking etc.

pax · 29 Aug 2006 at 15:28

emailiscrap said:
It doesn't. Switch on satnav whilst stationary and it doesn't know which way you are facing. It's only when you move that it assumes that the direction you are travelling in is forward. You can fool it by reversing as it will rotate the map as if you were facing the other way.

Spacky said:
Not so if you are using hand held ones for walking etc.

Walk backwards?

Pax

Bug One · 29 Aug 2006 at 15:28

Spacky said:
Not so if you are using hand held ones for walking etc.

I guess they've got a built in compass then.

My car GPS doesn't know until I start moving.

Borris · 29 Aug 2006 at 15:33

basmic said:
triangulisaratificalation

fixed

Tobeornottobe · 29 Aug 2006 at 16:14

works out range to minimum 3 satellites (latitude/longitude), 4 satellites (lat/long/altitude). Receiver works out the range by a clever trick of very exact time (satellites are linked to ground based atomic clocks) and doppler shift. If you know the exact range to four satellites, and the satellites know exactly where they are in relation to the earth, then your position can be exactly determined.

its called Triangomorphilication

basmic · 29 Aug 2006 at 16:20

Borris said:
fixed

This is what Google has to say.

shimy182 · 29 Aug 2006 at 16:23

http://electronics.howstuffworks.com/gps.htm

maybe howstuffworks.com might help a bit as well.

ElRazur · 29 Aug 2006 at 16:38

shimy182 said:
http://electronics.howstuffworks.com/gps.htm

maybe howstuffworks.com might help a bit as well.

Cool and thanks.

Also thanks to those who have contributed so far.....but guys, the rest of the question still stands.

PhilthyPhil · 29 Aug 2006 at 16:46

ElRazur said:
can anyone shed any light on how it is used to guide a missle to it target as there is no road or obstacle in the missile path?

The missile knows the coordinates of its target and it obtains its own coordinates from GPS. It can then compare them and plot a path to the target.

ElRazur said:
Also when a missiles locks on to a moving target is the gps responsible for this or the heat signature...?

I don't see how this could be done using GPS, I imagine it would either be the heat signature or some other method such as laser or maybe radar.

ElRazur said:
Do all ICBM have built in gps receivers?

Dunno

ElRazur said:
what will be the main differences/advantage between the new european satelite being put together at the moment over the GPS?

It is not controlled by the US military and it is meant to be more accurate I think.

Memphis · 29 Aug 2006 at 16:48

Something the all knowing El' doesn't know?! :eek:

Sleepy · 29 Aug 2006 at 17:01

ElRazur said:
Also when a missiles locks on to a moving target is the gps responsible for this or the heat signature.

Missiles aimed at moving targets use other means to locate the target. Such as IR, Radar, following a laser beam bounced off the target by a third party, manually controlled by a third party.

The JDAM bomb cannot be aimed at a moving target. They are testing bombs that use a laser guidance for final approach to a moving target and they are also testing a system that can update the GPS coords to steer the bomb onto a moving target.

MarcLister · 29 Aug 2006 at 17:10

ElRazur said:
what will be the main differences/advantage between the new european satelite being put together at the moment over the GPS?

Galileo will be more accurate, improved coverage of higher altitudes compared to GPS and since the US Military doesn't control Galileo, it can't "tune down" the accuracy of Galileo in times of war.

Currently, should the US go to war with another country (unthinkable I know), the US could reduce the accuracy of the GPS signal in the region of that country, thus giving the US military an advantage.

Check out http://en.wikipedia.org/wiki/Galileo_positioning_system for more info on the European alternative to GPS.

Beren · 29 Aug 2006 at 17:20

Wow another post designed to come up on the CIA/MI6 searches for counter-terrorism.

When are you next planning an international flight El? Expect rubber gloves and cold hands

What the others said about galileo, it's newer more accurate and can't be switched off by the US unless they blow it out of the sky...

The only way of using GPS to guide a missile to a moving target would be to have another device giving a live GPS point on the target... though thats a bit of an obvious point!

ElRazur · 29 Aug 2006 at 17:24

MarcLister said:
Galileo will be more accurate, improved coverage of higher altitudes compared to GPS and since the US Military doesn't control Galileo, it can't "tune down" the accuracy of Galileo in times of war.

Currently, should the US go to war with another country (unthinkable I know), the US could reduce the accuracy of the GPS signal in the region of that country, thus giving the US military an advantage.
.

Thanks man. The link was informative. You raised an interesting point - If the US can tune down a GPS signal over an enemy country...why do they bother about ICBM from countries like Iran and NK? Im asking this on the assumption that the "coordinates" enter into the rocket launch pad will rely on GPS right....?

Sleepy · 29 Aug 2006 at 17:30

ElRazur said:
Im asking this on the assumption that the "coordinates" enter into the rocket launch pad will reply on GPS right....?

They use other methods for navigation such as stellar and inertial. Its one reason they're not as accurate as US systems.

Sleepy · 29 Aug 2006 at 17:31

Beren said:
Wow another post designed to come up on the CIA/MI6 searches for counter-terrorism.

Don't worry about that dirtydogs posts have ensured we're all monitored by GCHQ/NSA