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So - If you were on the dark side of the moon (when you are part of the great gig in the sky) I think you would be unlucky - but on the side that faces the earth I reckon a decent receiver could pick up enough signals to make a fairly reasonable approximation.
My guess is that it would get screwy once you were above the astellites,
To obtain a position you make a comparison between the time signals transmitted by the satellites and the time you actually receive them, would not a problem arise because the time signals would be Earth time not Moon time.What the signals you receive would tell you would be where you are relative to the surface of the Earth as though you were flying above the Earth in an aircraft.I presume what you are interested in is where you are on the moon, no doubt this could be computed but it would be a complex problem.
Hang On, if you are on the moon...do you really need your GPS to tell you that......you're on the moon ?
Quote from: neilep on 27/03/2011 20:23:08Hang On, if you are on the moon...do you really need your GPS to tell you that......you're on the moon ?How else would you find the nearest McDonalds?
Quote from: Geezer on 27/03/2011 20:27:35Quote from: neilep on 27/03/2011 20:23:08Hang On, if you are on the moon...do you really need your GPS to tell you that......you're on the moon ?How else would you find the nearest McDonalds?Easy.Find the place with no atmosphere.
Syhprum - you are quite correct about the satellites. But how do they broadcast their signal? It would not take much leakage for the signals to be receivable on the moon. And three or more signals and a decent software algorithm and you have an exact position. So - If you were on the dark side of the moon (when you are part of the great gig in the sky) I think you would be unlucky - but on the side that faces the earth I reckon a decent receiver could pick up enough signals to make a fairly reasonable approximation.
"Sorry but the satalites that work for GPS are desined for the earth"The clocks in the satellites would run correctly on earth. They are designed for space.
" they work by trianglurisationaslism so you would need atleast two or three satalites to be involved,"There are 31 so, from the near side of the moon you could typically see a dozen or more.
"and also for those satalites and your GPS devices sofware to have a complete map of the moon."Nope, you can use a coordinate system based on earth anywhere, including the moon.
The receiver uses the messages it receives to determine the transit time of each message and computes the distance to each satellite. These distances along with the satellites' locations are used with the possible aid of trilateration, depending on which algorithm is used, to compute the position of the receiver. This position is then displayed, perhaps with a moving map display or latitude and longitude; elevation information may be included. Many GPS units show derived information such as direction and speed, calculated from position changes.
"Not forgetting all the time it would take for any signal to arrive from the moon to any satalite orbiting the earth"That delay is exactly how the system works.
"However, even a very small clock error multiplied by the very large speed of light — the speed at which satellite signals propagate — results in a large positional error. Therefore receivers use four or more satellites to solve for the receiver's location and time."
Although four satellites are required for normal operation, fewer apply in special cases. If one variable is already known, a receiver can determine its position using only three satellites. For example, a ship or aircraft may have known elevation. Some GPS receivers may use additional clues or assumptions (such as reusing the last known altitude, dead reckoning, inertial navigation, or including information from the vehicle computer) to give a less accurate (degraded) position when fewer than four satellites are visible
And would the accuracy even suck? It would be worse than on the surface of the earth but you would have a dozen or more points, with separations between them of up to 50,000km (they are in 20,000 km orbits) from a distance of around 400,000 km. The maths is beyond me, even if I did know what the inherent error margin were, but it doesn't strike me as too bad a deal - especially if there was no alternative.
To say "I was talking about the systems themselves being used with distances and time delays, that are set for earth, it's a given the satalites are designed to work in space."implies that you already know that answer, I contend that you don't.Of course, the system was designed to work on earth. So, in a sense, were people. But they still worked on the moon.There are plenty of instances of things designed for one thing but used for others. The internet wasn't designed for distributing naughty pictures, but that's one of its major uses.As for "A dozen or more:- facing the earth.", do you not realise that, for one thing , these were designed to spread a signal pretty much from horizon to horizon, and for another, antennae never form "perfect" beams- there's always some transmission in other directions?
"You mean based on a sphere shape,..."No, I meant what I said.A coordinate system based on earth (the one I had in mind was latitude, longitude and altitude) which can be used to pinpoint any place in the universe. Please don't presume to tell me what I mean."No, there are a few ways a GPS system can work, yet we are talking about the one we use."There may be several ways you could set up a GPS system.The one we use depends explicitly on exactly the time delays that you seem to think are a problem."And sending a signal from the moon to a satalite arround the earth would take too long, "Too long for what? The delay would be less than two seconds. How much of a hurry are you in?
"besides the fact that they are designed to communicate with systems on the earth."Still not important. It's not an issue of what they were designed to do, the question is about what they could do.
In principle, with the right decoding (normally restricted to military systems), a big enough aerial and the right software, you could find out your position on the moon by reference to the GPS system. The problems would be that it would give a result in earth based coordinates. But that's still telling you where you are. The other problem is that the accuracy would suck. That's not the same as saying it wouldn't work.
I think you'll find the satalite that sent it could have moved into a non reciving postion
Quote from: Wiybit on 01/04/2011 20:27:02I think you'll find the satalite that sent it could have moved into a non reciving postionIt doesn't matter if the signal disappears. The GPS receiver only needs to receive the satellite's signal once to determine a position.You might want to take a look at this http://en.wikipedia.org/wiki/Global_Positioning_System#Basic_concept_of_GPS
You are saying a device having recieved just one signal from one satalite while on the moon, will be able to tell you where you are.
Quote from: Wiybit on 01/04/2011 22:21:30You are saying a device having recieved just one signal from one satalite while on the moon, will be able to tell you where you are. No. I am not saying that at all. I am saying the receiver only needs to receive one transmission per satellite. Your point about the satellite moving is irrelevant.
Now look here Wybit, either admit you were wrong and you have learned something, or provide some substantial evidence to support your arguments. It looks like all you are doing is trying to change the subject whenever you are challenged.
Sorry, but that's nothing but trolling.
You can learn a lot on TNS (I have), but if you are confident you are always right, you are simply being a troll.It's your call. Are you trying to prove something, or are you trying to learn anything?
Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map.
◦Number of satellites visible - The more satellites a GPS receiver can "see," the better the accuracy. Buildings, terrain, electronic interference(which I believe includes solar wind interference), or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all. GPS units typically will not work indoors, underwater or underground.
"Personally I think only around 10% of the satalites up there at any one time could really transmitt in a luna direction anyway"Odd that, because, in reality, about half of them would (though the signal strength would be poor).
When you say "it's not so clear sent signal would reurn to the satalite that sent them," are you labouring under the delusion that GPS sends a signal back to the satellites? The GPS receivers are just receivers, not transmitters.
In other words, do you know what you are talking about? If not, perhaps you might think about learning rather than trolling.Incidentally, if you use Google chrome as a web browser it highlights spelling errors for you. That way you don't end up pontificating about satellites without even knowing how to spell the word.
NASA have already acknowledged that to use the Earths GPS system for navigation on the Moon is all but impossible and to set up a similar system to cover the moon would be extremely expensive.To this end they have let contracts to private companies to develop simple short range systems that will assist navigation on the moon.http://www.thaindian.com/newsportal/world-news/nasa-developing-navigation-system-for-moon-lead_10074436.html
Quote from: imatfaal on 25/03/2011 15:14:10So - If you were on the dark side of the moon (when you are part of the great gig in the sky) I think you would be unlucky - but on the side that faces the earth I reckon a decent receiver could pick up enough signals to make a fairly reasonable approximation.Why wouldn't it work on the dark side of the moon facing earth?
Quote from: Madidus_Scientia on 27/03/2011 07:41:18Quote from: imatfaal on 25/03/2011 15:14:10So - If you were on the dark side of the moon (when you are part of the great gig in the sky) I think you would be unlucky - but on the side that faces the earth I reckon a decent receiver could pick up enough signals to make a fairly reasonable approximation.Why wouldn't it work on the dark side of the moon facing earth?The "Dark Side of the Moon" has nothing to do with the sun or illumination.Rather, the moon is tidally locked with the earth. One side of the moon always faces the earth. One side (the dark side) always faces away from the earth. Thus, if you were on the side of the moon facing away from Earth... the GPS satellites would be useless.As far as whether you could use a GPS system.Obviously any software pre-programmed to positions on earth would be confused.Are the antennas omni-directional antennas? I don't see why you couldn't make basic triangulation routines to map a position in space above the satellites... and then map that onto the lunar surface based on lunar topography and the lunar orbit.
A time delay is irrelevant, and would just be part of the calculations. The geosynchronous orbit is about 36,000 km. The moon is at about 385,000 km. It is likely one could pick up satellites on all sides of the earth that are not eclipsed by the planet.
In fact, using the satellites on the far side of Earth, one should be able to pinpoint a location 385,000 km below the surface of the planet.
You can use GPS equipment in conjunction with a base station at a fixed location. Putting a fixed base station on the moon would likely greatly simplify the calculations, and significantly improve the accuracy of the system.Ahh...This base station would be essentially one approach for doing the local triangulation. One might be able to use the base station for calculating the offset even while not in direct sight of the base station.
The signals will be directed towards Earth and the distance to the Moon is 20 times further and just on that basis the signals would be 26 dB weaker (400 times less power). You would need a fair sized parabolic dish.. 3 metre or more.
Quote from: CliffordK on 02/04/2011 18:37:18 In fact, using the satellites on the far side of Earth, one should be able to pinpoint a location 385,000 km below the surface of the planet.Below the surface? What do you mean? GPS do not work indoors.
"Bored Chemist said no you didn't need a map and that GPS could tell you where you were any where in the universe. "Oh no I didn't.
"Based upon what do you make that acertion? "based on the fact that roughly half of them would be visible from the moon's earthward side and the laws of physics.
"I think you'll find the latest ones do blackberry and such like.http://us.blackberry.com/smartphones/features/gps.jspBut that is an assumption, Hence think."Red herring. It doesn't matter that Blackberies have a built in transmitter. There is no system on the satellites to receive a signal from them.You really haven't understood how GPS works.
Quote from: Wiybit on 02/04/2011 19:39:18Quote from: CliffordK on 02/04/2011 18:37:18 In fact, using the satellites on the far side of Earth, one should be able to pinpoint a location 385,000 km below the surface of the planet.Below the surface? What do you mean? GPS do not work indoors. [attachment=14363]
One of the more important aspects of satellite reception is the footprint of the satellite broadcasts you wish to receive. The footprint is the theoretical area covered by each satellite broadcast on the earth. Reception within this footprint will depend on dish size / LNB specs / receiver used also.