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
--
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