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posted by Fnord666 on Saturday April 25 2020, @08:32AM   Printer-friendly
from the shining-star dept.

Source: Musk says SpaceX is 'fixing' brightness from satellites:

Stargazers around the world and including many Britons have witnessed unusual constellations made up of the low earth orbit spacecraft.

SpaceX has been launching large batches of satellites as part of its Starlink project to improve global internet coverage.

The most recent launch took place on Wednesday.

Responding to a question about the brightness of the Starlink satellites on Twitter, Mr Musk said it was due to the angle of the satellites solar panels and the company was "fixing it now".

A fix could make them less visible from Earth.


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  • (Score: 3, Insightful) by maxwell demon on Sunday April 26 2020, @08:59AM (4 children)

    by maxwell demon (1608) on Sunday April 26 2020, @08:59AM (#987226) Journal

    The distance is much closer than GeoSyncSats.

    All the rain is below the orbit of all satellites, therefore the effect of rain should be independent on whether they are in GEO or in LEO.

    --
    The Tao of math: The numbers you can count are not the real numbers.
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  • (Score: 2) by Muad'Dave on Monday April 27 2020, @03:30PM (3 children)

    by Muad'Dave (1413) on Monday April 27 2020, @03:30PM (#987546)

    You're not taking total path loss into account when adding in the effect of rain fade. The base stations and sats have a fixed amount much power and antenna gain.

    The free space path loss [pasternack.com] for a 550 km orbit at 24 GHz is 175 dB. The FSPL to geosync (35,786 km) is a staggering 211 dB. That's 36 dB - a factor of 4000.

    Rain fade at 24 GHz [ui.com] can be as little as 0.2 dB/km for light rain and as much as 4 dB/km for a real frog-strangler. The troposphere is about 10 km thick, so we're looking at 2-40 dB attenuation from rain. A heavy rain is approximately the the same amount of attenuation as increasing the orbit from 550 km to geosync.

    If the link budget has < 40 dB available, then at geosync the rain will kill the connection.

    • (Score: 2) by maxwell demon on Tuesday April 28 2020, @06:47AM (2 children)

      by maxwell demon (1608) on Tuesday April 28 2020, @06:47AM (#987740) Journal

      You're not taking the intelligence of the system designers into account. GEO communication will occur at higher power than LEO communication, exactly because GEO satellites are higher up. Or in short, a system designed for the same performance/reliability will have higher sending power and/or more sensitive receivers in GEO vs. LEO.

      Therefore the effect of rain will reduce the actually received signal by the exact same amount.

      --
      The Tao of math: The numbers you can count are not the real numbers.
      • (Score: 2) by Muad'Dave on Tuesday April 28 2020, @11:04AM (1 child)

        by Muad'Dave (1413) on Tuesday April 28 2020, @11:04AM (#987779)

        I understand engineering link budgets for RF systems, and I never said the absolute rain fade was anything but exactly equal in both cases. What I did say was that _for the given antenna size and power levels_, the additional loss to geosync would likely push the existing budget past its limits (and perhaps past technological limits, i.e. noise floor or SNR).

        • (Score: 2) by maxwell demon on Tuesday April 28 2020, @02:56PM

          by maxwell demon (1608) on Tuesday April 28 2020, @02:56PM (#987835) Journal

          No one is going to take a satellite designed for LEO and put it into GEO. And at least GEO to ground during rain doesn't exceed physical limits, as my satellite TV reception proves.

          --
          The Tao of math: The numbers you can count are not the real numbers.