How do GPS work?

ElRazur said:
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 reply on GPS right....?
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Having read the Wiki link I think the US can turn the signal down internationally, not in local geographical area.

What the Americans hate most of all about Galileo is that it will be more accurate than their GPS, yet they won't control it and so they are scared their enemies could use it. In true US foreign policy the US government tried to convince the EU to cancel Galileo. Ironically, this reverse psychology didn't work because the EU decided to carry on with Galileo to develop some independence from the American GPS.

Perhaps the ICBMs from Iran/North Korea etc use other satellites to compute their location? Or perhaps radar or lasers? See the bottom of http://en.wikipedia.org/wiki/Icbm for info on different guidance missiles can use.
 
ElRazur said:
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....?
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It is the GPS accuracy around the target region that is important, since thats what the missile is aiming for - hence tuning down the GPS accuracy over countries like Iran wont help stop missiles from those countries. They could detune GPS over America, but then Americans would be annoyed. Also a nuke hitting 10 miles away from where it should have hit is pretty much just as bad - its not like the 'enemy' cant launch reasonably accurate missiles which dont use GPS.
 
Lagz said:
Also a nuke hitting 10 miles away from where it should have hit is pretty much just as bad
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Only if they got multi stage hydrogen bombs, an A bomb at that range is just a pretty firework.
 
Here is a basic summary of how GPS works (I did a bit of work on GPS last year):

GPS satellites are controlled by the US from base stations. The base stations upload orbital data and clock skew corrections to the satellites, which then transmit this data along with a repetetive code, which is indistinguishable from noise UNLESS you know the code.

A GPS receiver knows the code transmitted by each GPS satellite. The receiver basically searches for the known codes (which it can extract from the noise). Having locked on to 4 codes from 4 satellites it is able to resolve its position in 4D space (x,y,z,time). The reason it must also resolve its position in time is because GPS receivers dont have accurate clocks - and any clock skew will cause positioning errors.

To degrade the signal the USA can basically upload dodgy orbital or clock skew data to the satellites. This will affect any GPS receiver which is using that satellite. The USA no longer degrade signals.

There is also a technique called Differential GPS - which allowed used to easily bypass signal degradation. If you establish a GPS receiver at a known stationary point nearby you can observe exactly how the signal is being degraded (by observing how the position of the supposedly stationary point changes over time). You can then transmit this information to your mobile GPS receivers which can subtract the errors and hence obtain accurate positions.
 
tntcoder said:
What powers GPS and Imaging satellites? I assume they do need power? Is it just some kind of uber long life battery.
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I would assume solar powers....i was gonna say nuclear but it wont make sense. :p
 
ElRazur said:
I would assume solar powers....i was gonna say nuclear but it wont make sense. :p
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You'd be surprised, deep space probes such as Pioneer and Voyager and New Horizons are powered by plutonium. They go too far out for solar panels to work
 
Visage said:
Some satellites and probes use nuclear power, there was a big controversy a few years back over the launch of a probe that was nuclear powered.

I think it was Cassini.

EDIT: yes it was: http://www.cnn.com/TECH/9710/10/cassini.advancer/
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:eek:

This sums up my feeling i guess
"I'm not anti-nuclear. I'm not anti-technology. I'm not anti-space program. But I'm anti-stupid, and this is stupid," summed up protester Harold Courtright.
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Sleepy said:
What the rantings of some ignorant nut job?
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lol, i dont see it that way....I dont know if that project will be hoovering over the earth, but if so.....dont sound too good though. Think of the consequences if it drops (or maybe not, might burn up before entering the atmosphere......what about the fall out or residue from it....Sounds crazy, i know, but a possible scenario) :p
 
ElRazur said:
lol, i dont see it that way....I dont know if that project will be hoovering over the earth, but if so.....dont sound too good though. Think of the consequences if it drops (or maybe not, might burn up before entering the atmosphere......what about the fall out or residue from it....Sounds crazy, i know, but a possible scenario) :p
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Its orbiting Saturn so the chances of its falling to earth now are zero. Anyway 72Ib of Pu falling to earth isn't very exciting or scary or dangerous. The fearmongers are using ignorance plus the irrational fear of radiation to generate controversy.

Edit Pu isn't very radioactive.
 
Sleepy said:
Its orbiting Saturn so the chances of its falling to earth now are zero. Anyway 72Ib of Pu falling to earth isn't very exciting or scary or dangerous. The fearmongers are using ignorance plus the irrational fear of radiation to generate controversy.

Edit Pu isn't very radioactive.
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Ohh i see now, you are right the guy is a nutjob.
 
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