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ArcticMyst Security by Avery
GPS sattelites
- Thread starter tatman
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Benm
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I doubt it would do you any good really.. if you can see those sats, they are bathing in sunlight and reflecting that towards you. Illumination with a laser pointer at such disntaces would be minimal, even when ran through a telescope.
as long as you don't intentionally interfere with aircraft laser away.
I've many times wondered if I could laser the space station while it was live on Nasa TV to see if they could see it.
Have to use something powerful and visible though maybe a 40-60W copper vapor laser.
I've many times wondered if I could laser the space station while it was live on Nasa TV to see if they could see it.
Have to use something powerful and visible though maybe a 40-60W copper vapor laser.
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Good luck. GPS satellites are in MEO (medium earth orbit), 12,000+ miles (20,000 km) in altitude and traveling 14,000 km/hr. If you point your laser at the satellite where you see it in space, by the time the beam reaches it, it will have moved 15.55 km. Then of course, you would have to have one heck of a long focal length lens to put a spot on the satellite if you could keep up with it's motion. There are also some relativistic effects due to the velocity of the satellite on your perception of it's location.
Benm
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Reminds me of the lunar range finding experiments, where they even have retroreflectors on the surface. As i understand they only get to detect a few photons a second, even working with powerful lasers and telescopes.
The moon obviously is 10x further away than MEO sats, but it gives you an idea of the problems involved.
The moon obviously is 10x further away than MEO sats, but it gives you an idea of the problems involved.
Its a nice though but its not even the question of laser power and focal lenght.
I dont think that the mechanics needed to keep the spot on a fast moving satelite at theese distances exist.
Considering that the GPS satelites have to compnensate for Einstein in every day work, the relativistic effect definately would have to be taken into account and that would be super-tricky if not impossible from the mechanical poit of view.
The lag of a 20,000 km/h satelite do to special ralativity would be about 1/15 of a second and belive me...this is enough for it to travel quite a lot. If the speed is constant the lag would also be constant so lets assunme this is duable.
There would also be significant lags do to general relativity (Gravity) as the satelite changes its distance from earth while going around it in an elispe. These lags would not be constant and I cant imagine how to compensate for these without having a freakin Nasa station.
I dont think that the mechanics needed to keep the spot on a fast moving satelite at theese distances exist.
Considering that the GPS satelites have to compnensate for Einstein in every day work, the relativistic effect definately would have to be taken into account and that would be super-tricky if not impossible from the mechanical poit of view.
The lag of a 20,000 km/h satelite do to special ralativity would be about 1/15 of a second and belive me...this is enough for it to travel quite a lot. If the speed is constant the lag would also be constant so lets assunme this is duable.
There would also be significant lags do to general relativity (Gravity) as the satelite changes its distance from earth while going around it in an elispe. These lags would not be constant and I cant imagine how to compensate for these without having a freakin Nasa station.
tatman said:
If youre atracted to physics in any remote way I recommend Brian Greene's "The Elegant Universe" Its writen in lay mens language and its a real treat to read. Theres also a 3 part movie series under the same title from PBS Nova. You can get it on torrents, Ive wtached it twice and its as good as the book
gps sats as well as most tv and weather sats are geostationary. they move just as fast as the earth moves/rotsates, so as far as we are concerned they don't move. if you had the right coordinates you could hit them all day and night long, only the spy sats and imagery sats move because they have to be so close to the earth for good resolution.
koti said:
for most sats the lag is meaningless, the radio waves move at nearly the speed of light to you dont need to bother theres just a slight doppler shift. the signal drifts one way or the other, for the geostationary sats, the signal doesn't vary much at all. it's harder to account for doppler shift of your cell phone while you talk and drive on the highway than it is for most satellites. even our internet connections lag randomly. there's no interference at all in space unless it's solar. the distances are fixed for the most part so you have a predetermined amount of lag both ways. that's cake to account for.
Aseras said:
All GPS satellites have to compensate for special & general relativity, its a a fact.
In my opinion, You wouldnt be able to calibrate any kind of mechanical aparatus to keep the laser spot on the satelite for more then a fraction of a fraction of a second without taking Einstein into account. However You look at it though, it would be nothing close to "cake to account for"
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GPS satellites are not geosynchronous. They would have to be out at about 22000 miles to be geosynchronous. some move with the rotation of the earth, some against and some perpendicular with most exhibiting some form of both x and y motion.
Yes GPS sats do compensate for relativistic motion but that's only for their internal atomic clocks. It is the laser wielder that needs to account for relativity when firing at the GPS sat.
Yes GPS sats do compensate for relativistic motion but that's only for their internal atomic clocks. It is the laser wielder that needs to account for relativity when firing at the GPS sat.
tatman said:
Coming back to the scubject;
It would be difficult and extremely expensive to construct a guiding system that would be capable of kepping a laser beam over a decent amount of time on a GPS satelite in orbit. Not mentioning the far out laser specs needed...power, divergence etc.
Theoreticaly its possible (then again wormhole time travel is as well) but it would take a realy rich and seriously commited freak to make this happen.
I like the idea though...it would be a huge milestone for man kind to achieve this
