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Old 2006-03-23, 15:16   #1
mfgoode
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Lightbulb Broadband in space?

Currently many spacecraft still use radio signals to send data back to Earth.
Two way laser communication in space seems to be the answer

http://www.space.com/businesstechnol..._detector.html
Mally
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Old 2006-03-23, 16:21   #2
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How difficult is it to precisely hit the detector over such a long distance?

AFAIK, the radio signals used have a certain angle, which avoids this problem...
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Old 2006-03-23, 20:01   #3
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Quote:
Originally Posted by Mystwalker
How difficult is it to precisely hit the detector over such a long distance?

AFAIK, the radio signals used have a certain angle, which avoids this problem...
Well, the US Military has been using lasers to send data to submarines from sats for a while. And for that matter they also use ultra low bit rate, extremely low frequency radio (3-10Hz, not kHz).

Lasers also have an angular spread. Dust and atmospheres will scatter it. With the mentioned system, rovers etc. would use radio locally to send data to an orbiter that would act as a comsat. The lasers that are used to do distance checks to the moon spread out to ~1km on the transit out there (that was as of ~25 years ago). They were aimed at the Apollo sites with a target the size of a large stop sign.
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Old 2006-03-27, 03:20   #4
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I've seen one of those lasers. When I went to Georgia Tech, they used to do rangefinding on the moon reflectors at night sometimes. At leat that is waht i was told the bem going into the heavens from the top of one of the buildings was.
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Old 2006-03-27, 18:38   #5
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Quote:
Originally Posted by Uncwilly
The lasers that are used to do distance checks to the moon spread out to ~1km on the transit out there (that was as of ~25 years ago).
Current lasers might be getting closer to that, but 25 years ago it was more like 6-7 KM.

Only about 1 in a billion photons that were sent out reached the detectors back on earth.
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