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The main refraction of the two frequencies, separated by about 300 mhz, occurs in the ionosphere. Then the difference in time of the reception of the signals allows for the calculation of a distance from each satellite. Also GPS is used for distibution of UTC timing, which is similiar to WWV/WWVH Timeing distribution, only WWV/WWVH is through NIST and GPS is Done through USNaval Observatory.
This timing would be key for highspeed communications.
We are only limited by our Will and our Imagination.
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Acording to *The Case for Mars,* pages 157-58, Mars does have an ionosphere, but it is 1/25th as dense as the Earth's (in terms of density of charged particles). So it will reflect ham radio wavelength signals and AM radio signals. Zubrin also notes the Martian atmosphere is less noisy in the radio frequency; fewer electrical discharges. Maybe it will refract GPS signals as well, especially if a longer wavelength were used. Another problem: the density of the ionosphere may vary more than the Earth's. When there are duststorms the density of the upper atmosphere increases measurably and aerobraking actually has to be moved to higher altitudes. The ionosphere may move up and down as well. But I suppose solar flares change the Earth's ionosphere a lot as well, so maybe GPS can compensate.
-- RobS
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I have some information on GPS, but I don't know whats public knowledge and whats not, but I do know that there is various ground locations that when a GPS Satellite passes overheard, it pick up all the ephermis (spelling) Data and gives corrections. I also imagine that it maybe possible to use a different system to determine distance from the satellite. I'll have to think on that one. I guess I need to read a Case for Mars. I also imagine that one could use different frequencies maybe a wider separation to ensure more accuracy? like something in high vhf and something in High UHF. Push it up a little higher just under the skin effect issue. I think it maybe possible to use a terrain following system, or an inertial system similiar to advanced gyroscopes used in Pre-GPS Avionics coupled with a few satellites that have very short periods that could actively lock in on a target and send it Lat. Long and Alt updates. If you could manufacture a simple fairly accurate guidance system, and then have one or two satellites, it may be less expensive. Then have one ground station that would send updates and check Satellite ephermis data.
We are only limited by our Will and our Imagination.
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The two frequency GPS is for keyed or P-Code GPS operation. It is much more accurate then the single frequency GPS operation. So, it can be done with one frequency, but if your doing one you might as well do two or three for increased accuracy.
We are only limited by our Will and our Imagination.
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It seems to me that at the start highly accurate navigation is not that necessary. Certianly knowing you possition down to the cm is extream for the start. The rovers don't have to drive themselves, the highly trained astronauts can do that as well.
Also not mentioned, but certianly VITALY important are MAPS! Without a map knowing where you are and where you want to go may be worthless because you may not be able to get there from here (like there's a big canyon bettwen you two). A good map can also help you figure out where you are by identifing the terrian features and landmarks. While Mars is not Earth it still will have prominate landmarks and landformes.
Even while in the boy-scouts my patrol and I had little trouble with 10-12 mile orientation hikes using just our compasses and a map. Certianly highly trained astronauts with good maps, sextants, and internal navigation will be able to do better than I, even on a alien planet over larger distances. Indeed in some ways the sparsness helps. In the woods my "horizon" was only a couple of hundred feet away, and I (and my buddies) could only transmit as far as our voices could carry. Since NASA has so many Eagle Scouts, shurely one of them earned his wilderness survival merit badage and can help find where they are. So only the slimist of GPS systems should realy be needed at the start.
Not to encourage the defacment of an virgin enviroment, but the astronauts could easily mark there trail as they go as well. This would slow them down certianly, but would make getting lost very difficult. It's funny to think of an some one in a space suit with a can of blue paint, marking his trail on a red-rock but such a system could be very effective.
To help facilitate the return to important areas they could carry small radio beacons with them as well. All that would be needed would be a little solar pannel and an antenna it probably wouldn't have to put out that much juice since all it has to do is beep (and not even that frequently, one a half-hour or so would be more than sufficent). Put these on diffrent frequencies, and once the come over the horizon they could tune in the frequency, and easily find the spot with a little simple trig.
Also, for safties sake more than anything else, astronauts shouldn't leave the base or the rover over the horizion anyways. Even on Mars thats more than a short walk, and they shouldn't get that far away from a hab or rover lest there suit rip or something if nothing else. So even if the astronaut does get lost on a walk, all he has to do is climb the nearest hill, he should be able to SEE the rover/hab but if not he should be able to pick it up on radio. And if that fails, he should stay put and the rest of the guys go look for him. Individual GPS units are overkill. You might need one in the rover, but it could have a large reciver so your satilite could be smaller.
Also, just because there's not a strong magnetic field doesn't mean you can't find your berrings. If you know the time of day you can use the sun, and at night you can use the stars.
To some up, I don't think to much money and space should be wasted on navigation on Mars which realy shouldn't be that difficult. Good maps (important in any case), maybe a satilite or two to help find position, good use of radio transmiters, and some basic stuff in the rovers (sextant, computer, ect...) and any Eagle Scout should be fine.
He who refuses to do arithmetic is doomed to talk nonsense.
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It seems to me that at the start highly accurate navigation is not that necessary. Certianly knowing you possition down to the cm is extream for the start. The rovers don't have to drive themselves, the highly trained astronauts can do that as well.
Also not mentioned, but certianly VITALY important are MAPS! Without a map knowing where you are and where you want to go may be worthless because you may not be able to get there from here (like there's a big canyon bettwen you two). A good map can also help you figure out where you are by identifing the terrian features and landmarks. While Mars is not Earth it still will have prominate landmarks and landformes.
Even while in the boy-scouts my patrol and I had little trouble with 10-12 mile orientation hikes using just our compasses and a map. Certianly highly trained astronauts with good maps, sextants, and internal navigation will be able to do better than I, even on a alien planet over larger distances. Indeed in some ways the sparsness helps. In the woods my "horizon" was only a couple of hundred feet away, and I (and my buddies) could only transmit as far as our voices could carry. Since NASA has so many Eagle Scouts, shurely one of them earned his wilderness survival merit badage and can help find where they are. So only the slimist of GPS systems should realy be needed at the start.
Not to encourage the defacment of an virgin enviroment, but the astronauts could easily mark there trail as they go as well. This would slow them down certianly, but would make getting lost very difficult. It's funny to think of an some one in a space suit with a can of blue paint, marking his trail on a red-rock but such a system could be very effective.
To help facilitate the return to important areas they could carry small radio beacons with them as well. All that would be needed would be a little solar pannel and an antenna it probably wouldn't have to put out that much juice since all it has to do is beep (and not even that frequently, one a half-hour or so would be more than sufficent). Put these on diffrent frequencies, and once the come over the horizon they could tune in the frequency, and easily find the spot with a little simple trig.
Also, for safties sake more than anything else, astronauts shouldn't leave the base or the rover over the horizion anyways. Even on Mars thats more than a short walk, and they shouldn't get that far away from a hab or rover lest there suit rip or something if nothing else. So even if the astronaut does get lost on a walk, all he has to do is climb the nearest hill, he should be able to SEE the rover/hab but if not he should be able to pick it up on radio. And if that fails, he should stay put and the rest of the guys go look for him. Individual GPS units are overkill. You might need one in the rover, but it could have a large reciver so your satilite could be smaller.
Also, just because there's not a strong magnetic field doesn't mean you can't find your berrings. If you know the time of day you can use the sun, and at night you can use the stars.
To sume up, I don't think to much money and space should be wasted on navigation on Mars which realy shouldn't be that difficult. Good maps (important in any case), maybe a satilite or two to help find position, good use of radio transmiters, and some basic stuff in the rovers (sextant, computer, ect...) and any Eagle Scout should be fine.
He who refuses to do arithmetic is doomed to talk nonsense.
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I agree, simplistic navigation would work better, maybe a really simple inertial system in a rover coupled with an on board map may be much cheaper and just as effective as GPS.
Also there is over 24 GPS satellites in orbit with a cost of over 200 million a pop. I think a 7 1/2 minute map and a good Brunton Compass will get you pretty far and also initial going to far from base camp is a bad idea. I think the K.I.S.S. idea works best here.
We are only limited by our Will and our Imagination.
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