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Reflecting satellites, big business
David Jonsson wrote in
: Someone mentioned detecting the signal on the satellite and retransmitting it but that would involve electronics and would cut off anything above some 10 GHz where electronics become too resistive. The laser signal has a frequency of hundreds of THz and is thus capable of 10 000 times higher data transfer. The laser is not a modulated EM carrier like in typical radio wave communications (eg FM/AM). The laser is pulse modulated in an on/off fashion. Therefore the amplification being talked about is to receive the signal at the satellite, decode the data, then re-encode it on a new laser for the return trip. A low orbit satellite would be moving around all the time making a stable link between two points impossible. Right, round trip times makes a low earth orbit satellite necessarry with the telescopes being redirected all of the time. Moving them does not look like a big issue. Do you know how long a low orbit satellite is 'visible'? A few minutes. A pass of the ISS lasts maybe 5-7 minutes - and that's from 10 degrees off each horizon and assuming a perfect zenith pass. (visual sat tracking is a side hobby of mine) Perfectly tracking a satellite with a narrow laser beam would require a sophisticated tracking mount. Further, the satellite would also be required to use sophisticated tracking and orientation stabilization to aim the laser at the receiving station. Whereas with a geostationary satellite, the satellite only has to maintain attitude control, and the ground station is fixed with no moving parts. Although with laser, a higher level of aiming precision may be required due to the narrowness of the beam compared to microwave frequencies. However more tan 95% of internet traffic is not real time Cite? and would not suffer from a delay of 200 ms in a geostationary orbit. Assuming a latitude of 45 degrees and being on the meridian of the satellite, the one-way light time is 253 milliseconds. The total latency is around 1 second for geostationary communications. The signal has to go up to the satellite, then back down, and this is only for the data request. Then the returning data has to make the same trip. I am currently on satellite internet and I just did an online speed test the meased my latency as around 950 milliseconds. The way Internet traffic is sold makes even this kind of traffic valuable. Imagine the high cost of an Atlantic cable. Still a lot cheaper to the end user than satellite. A physical cable can carry magnitudes more data than a satellite (even laser), and costs less to install. The only advantage of satellite communications is that it allows SOME communication where there is no hardwire. Brian -- http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism Seismic FAQ: http://www.skywise711.com/SeismicFAQ/SeismicFAQ.html Quake "predictions": http://www.skywise711.com/quakes/EQDB/index.html Sed quis custodiet ipsos Custodes? |
#12
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Reflecting satellites, big business
In article ,
Skywise wrote: The way Internet traffic is sold makes even this kind of traffic valuable. Imagine the high cost of an Atlantic cable. I believe there are perfectly functional, less than 20-year-old transoceanic fiber cables that have simply been abandoned in place on the ocean floor, because the latest cables have such immense traffic-handling capability that these older cables are simple not needed, and it makes no sense to continue to operate them. The loaded cost of transferring bits through an Atlantic cable **per telephone call* or **per file transferred** is just unimaginably small -- truly "bandwidth almost too cheap to monitor or to measure". |
#13
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Reflecting satellites, big business
AES wrote in news:siegman-6A2D86.10041017052010
@bmedcfsc-srv02.tufts.ad.tufts.edu: In article , Skywise wrote: The way Internet traffic is sold makes even this kind of traffic valuable. Imagine the high cost of an Atlantic cable. I believe there are perfectly functional, less than 20-year-old transoceanic fiber cables that have simply been abandoned in place on the ocean floor, because the latest cables have such immense traffic-handling capability that these older cables are simple not needed, and it makes no sense to continue to operate them. The loaded cost of transferring bits through an Atlantic cable **per telephone call* or **per file transferred** is just unimaginably small -- truly "bandwidth almost too cheap to monitor or to measure". Exactly. This whole satellite based laser system is just a Rube Goldberg idea. IMO. It may have certain niche uses, but not for general consumption. Brian -- http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism Seismic FAQ: http://www.skywise711.com/SeismicFAQ/SeismicFAQ.html Quake "predictions": http://www.skywise711.com/quakes/EQDB/index.html Sed quis custodiet ipsos Custodes? |
#14
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Quote:
Thanks you for the post. |
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