New light-based modem to transmit 100x faster than radio signals

Discussion in 'General Science & Technology' started by Plazma Inferno!, Feb 1, 2016.

  1. Plazma Inferno! Ding Ding Ding Ding Administrator

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    NASA is developing a first modem that incorporates light-based technology to help enable dramatically faster communications between spacecraft and ground stations.
    The device, which is scheduled to be tested on board the International Space Station in 2020, is part of a broader NASA project called the Laser Communications Relay Demonstration (LCRD). This laser system, which the space agency says could dramatically overhaul today's radio frequency (RF) communications, will enable data transmissions at rates 10 to 100 times faster than what's currently possible.

    http://www.sciencealert.com/nasa-s-...o-100-times-faster-than-today-s-radio-signals
     
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  3. danshawen Valued Senior Member

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    If this technology involves beaming infrared or other lasers to / from the ground from Low Earth Orbit spacecraft, I don't see how this could be done without the system posing a hazard to commercial aviation. The FAA already complains that the incidents of ground based laser pointers are hazardous to pilots at altitudes of thousands of feet, but particularly at critical times during the flight which would include takeoffs and landings.

    https://en.wikipedia.org/wiki/Lasers_and_aviation_safety

    The downlink (to the ground from orbit) might not pose much of a aviation safety problem, but the uplink (from the ground to the spacecraft) almost certainly will.

    Also there is the issue of clouds and other laser energy absorbing atmospheric conditions, which would hamper both acquisition and tracking of the laser signals.
     
    Last edited: Feb 2, 2016
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  5. spidergoat pubic diorama Valued Senior Member

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    It's just lights, like the lights you see all around us in fixtures. They would have to be LED though.
     
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  7. billvon Valued Senior Member

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    1) Infrared light is invisible.
    2) They will likely use beam expanders, so even though the total power will be higher the energy intercepted by a human eye will be extremely low.
     
  8. danshawen Valued Senior Member

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    1) Infrared lasers are used for performing radial keratotomies and can damage retinas the same way visible lasers do.

    2) The compromise you are suggesting (expanding the beam) may reduce the S/N (signal-to-noise) ratios to levels that are useless to the type of telecommunication the OP mentions. Much of the geostationary satellite telecom industry currently depends on spot beaming microwave signals. LEO satellites have less path loss and are used for things like GPS, which don't need satellite dishes to work with mobile phones, but mobile phones don't uplink anything to them. If they did, it would need to transmit several Watts of power in a hemispherical configuration, like the old IRIDIUM global satellite phones did. Infrared replacements for microwave transmitters to LEO satellites would need to be about the same or even more power.
     
  9. billvon Valued Senior Member

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    The lasers used for RK/Lasik are specifically designed to be absorbed by the cornea, rather than being passed through to the retina. That's how they work.

    Of course, any light source can be damaging to the eye if intense enough.
    Why do you think that?
    Why would an optical link use such a non-directional transmit pattern?
    Why do you think that? Why do you think you would need the same transmit power to achieve the same Eb/No?
     
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  10. danshawen Valued Senior Member

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    Making an optical link directional on the uplink is EXACTLY what I said posed a danger to commercial aviation, because the most economical way to make that happen, with the best signal-to-noise ratio, is with laser optics, with or without error correction.

    LEO satellites cross from horizon to horizon in about 15 minutes. It takes swarms of them to do what IRIDIUM did, and GPS does. Imagine the sky filled with IR satellite tracking lasers. Get the picture.
     
  11. billvon Valued Senior Member

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    And as I said, most optical links use beam expanders to reduce intensity, increase collimation and avoid dropouts due to precipitation. Thus they will not pose a threat to commercial aviation.
    Yep. No problems from an aviation standpoint; the intensity of the light would be far less than the intensity of (say) the ALS they will see when they are landing.
     

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