A Space & astronomy forum. SpaceBanter.com

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Satellites
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Reflecting satellites, big business



 
 
Thread Tools Display Modes
  #11  
Old May 16th 10, 09:09 PM posted to sci.astro.satellites.visual-observe,alt.lasers,sci.optics
Skywise
external usenet poster
 
Posts: 318
Default 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?
Ads
  #12  
Old May 17th 10, 06:04 PM posted to sci.astro.satellites.visual-observe,alt.lasers,sci.optics
AES
external usenet poster
 
Posts: 11
Default 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  
Old May 17th 10, 07:30 PM posted to sci.astro.satellites.visual-observe,alt.lasers,sci.optics
Skywise
external usenet poster
 
Posts: 318
Default 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  
Old September 22nd 11, 10:37 AM
bella10388 bella10388 is offline
Junior Member
 
First recorded activity by SpaceBanter: Sep 2011
Posts: 1
Default

Quote:
Originally Posted by David Jonsson View Post
Hi

Can anyone help me determine how much data that is physically possible
to transport with a beam of light from Earth reflected on a satellite
back to Earth again with an good reflector?

I made a fast calculation on the moon and found that since the mirror
is distributed over a distance of 0.1 m a difference in time of the
signal of one nanosecond will occur limiting the bitrate to maximum
one gigabit per second which is not worth transporting. On the other
hand maybe 1000 different light frequencies can be used making it
possible to sell the data flow for $ 500 000 per month.

To find out if it is worth doing assume a transport price of 0.5 $ per
megabit per second for one month (approx 600 gigabyte per $).

Is it worth building, place in orbit and maintain such a satellite?

I can imagine a low orbit satellite with a big concave mirror, a plane
mirror in the focal point and another big concave mirror aiming the
reflected beam back to earth in a non diverging beam to another place
on Earth. Precision would be at least 1 000 higher than the Moon
example giving a cash flow of billion $ per month.

How much would the atmosphere distort this signal?

Someone might complain about clouds blocking the signal but it would
anyway be valuable for cloud free moments. Internet operators could
save money whenever the sky is clear.

David

David Jonsson, Sweden, phone callto:+46703000370

Thanks you for the post.
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Help with reflecting telescope Marco Dorantes Amateur Astronomy 5 March 5th 08 04:11 AM
Please Need Help about 114mm Reflecting telescope duke Amateur Astronomy 5 July 26th 06 01:17 AM
A reflecting film for heating planets OlegMGoryunov Solar 1 January 14th 06 10:37 AM
non-reflecting coating Jimcat Amateur Astronomy 1 November 29th 04 03:38 AM
reflecting sunlight onto the Moon? Joe Strout Policy 69 May 21st 04 10:23 PM


All times are GMT +1. The time now is 10:05 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright 2004-2018 SpaceBanter.com.
The comments are property of their posters.