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Communications Networking Shark Moon NASA Space

NASA Testing Frickin' Laser Communications 108

Posted by timothy
from the beam-it-up-scotty dept.
itwbennett writes "The lunar laser communications demonstration will be part of the agency's Lunar Atmosphere and Dust Environment Explorer (LADEE) mission, which is scheduled to launch on Sept. 6. Here's how the system will work: When the satellite is in orbit around the moon and visible from Earth, one of three ground stations will shoot a laser towards its approximate location. The laser beam from Earth will scan a patch of sky and should illuminate the spacecraft at some point. When that happens, the spacecraft will begin transmitting its own laser towards the ground station and the two will lock on to each other. The technology should allow an upstream data rate, from the Earth to the spacecraft, of around 20Mbps and a much faster downstream rate of 622Mbps. That's roughly six times the speed that's currently possible with radio-based transmission, said Don Cornwell, mission manager for the lunar laser communications demonstration."
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NASA Testing Frickin' Laser Communications

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  • A long time coming (Score:4, Informative)

    by mbone (558574) on Saturday August 24, 2013 @11:53AM (#44664179)

    One of the weaknesses of the NASA science / PI driven culture is that engineering tests like this can take a very long time to fly, as they do not directly provide science and have no scientific community demanding them. Laser communications was proposed for testing on the space station (as a down-link site) in the 1980's, has made it close to getting into space several times, but every previous attempt to fly it was eventually canceled to save money. Now, finally, it will be tested (or, in NASA speak, achieve a TRL of 8).

    As it is, numerous deep space missions are data limited, such as the Mars Reconnaissance Orbiter, which could take more pictures, if it could get the data back. Laser comms is badly needed, let's hope the LADEE test goes well and it can finally get deployed.

  • by mikael (484) on Saturday August 24, 2013 @12:17PM (#44664337)

    Probably the laser will probably in a wavelength of light that clouds don't absorb. There are a few "infra-red windows" that can be used.
    http://www.st-andrews.ac.uk/~bds2/ltsn/ljm/JAVA/SPECTRUM/details.html [st-andrews.ac.uk]

    Then they'll use TCP/IP adapted for space communication - modifying the protocol to handle time lag. That's more or less what it was like using the "Kermit" protocol with a 9600 or 19200 baud modem (~960 characters/second) - we used to "turbo boost" our connections by using large packets (1024 bytes). Even so, five packets could be sent down, in the time it took the other end to calculate the CRC's and send back the acknowledgement.

    It's better than what they have now, so they won't complain.

  • by girlintraining (1395911) on Saturday August 24, 2013 @01:09PM (#44664607)

    Probably the laser will probably in a wavelength of light that clouds don't absorb. There are a few "infra-red windows" that can be used.

    Ah, this link [wikipedia.org] might be a bit more useful in explaining the phenomenon to which you're referring.

    The thing is, these windows are not very big, and there are only two big ones. What's worse, clouds still scatter and mush up the signal... it may not be absorbed, but that doesn't mean it won't go all over the place. It'd be like trying to piss in a hurricane... good luck getting a straight stream into the toilet in wind gusts that'll get you my pretties (and your little dog too).

    It's only useful in dry atmosphere. Fortunately... guess where they put the communications array. :) I'll give you a hint: Not Seattle.

  • by mbone (558574) on Saturday August 24, 2013 @01:37PM (#44664805)

    I have talked with the people doing the laser comm experiment on LADEE - it is just a technology demo, and is not needed for the LADEE mission primary science goals at all. (That is the difference between a science mission, such as LADEE, and a technology demonstration mission, such as Deep Space 1, where the science is secondary and can depend on the successful working of the new gizmo.)

    If it works on LADEE, then someone can propose doing it on a real mission (i.e., one that would depend on it), just as the ion engines from Deep Space 1 are now powering DAWN.

  • Re:Huh? (Score:3, Informative)

    by Anonymous Coward on Saturday August 24, 2013 @02:01PM (#44664939)
    The Terra satellite was also almost 5 tons in mass with 2.5 kW of power to work with in low Earth orbit. LADEE is a twentieth of the mass, with a tenth of the power budget, and in lunar orbit. The situations are different, and it is like you are complaining a 1000+ HP car is trivial because cargo ships do that all the time.

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