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Radio Blackouts: Their Causes

  1. Jun 19, 2015 #1
    What causes radio blackouts to occur when, for example, a manned space capsule is descending through the Earth's atmosphere? If the atmosphere itself is in some way responsible for these blackouts (as surely it must be)* then how exactly? NB. Surely it can't be due to the ionosphere. I suggest this because footage of Apollo 13 reveal that its crew were in a state of radio incommunicado with Mission Control during the latter stages of their descent to Earth - that is, until their capsule was seen to emerge from the base of what appears to have been a fairly low cloudbank. Somehow, I can't quite believe the ironosphere extends to such depths. Just an observation.

    * I don't recall this sort of thing happening during the actual Moon-landings, for example.
     
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  3. Jun 19, 2015 #2

    phinds

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    I think it's the red-hot plasma created by the friction heat during reentry.
     
  4. Jun 19, 2015 #3

    Vanadium 50

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    phinds is right. If you Google "radio blackout during reentry", you get this page: https://en.wikipedia.org/?title=Communications_blackout which has a whole section on it, beginning:

     
  5. Jun 19, 2015 #4

    russ_watters

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    When you say the "footage" of Apolo 13, are you referring to the Hollywood movie? That movie is not a documentary, it is a dramatization and fine details are not necessarily accurate. Here's the full explanation:
    http://www.universetoday.com/119921...longer-than-expected-communications-blackout/
    Note also that better communications equipment has eliminated the blackout for modern spacecraft.
     
  6. Jun 19, 2015 #5
    Russ: rather than the Hollywood movie, I was referring to the actual 'live' footage of the Apollo 13 descent, filmed (if my memory serves me well) onboard a US aircraft carrier somewhere in the Pacific. Yes, this scene is also included in the movie, as I recall. Nevertheless, I should have made the distinction clearer.

    So it appears then that the radio blackout problem is now largely eliminated. If so, and wearing my SF hat for the moment, does this mean then that an astronaut onboard a decelerating spacecraft, powered (say) by a fusion drive, would be able to direct a radio (or laser?) signal through the plasma exhaust to a given destination located further astern the spacecraft? Or is this still a speculation too far?
     
  7. Jun 19, 2015 #6

    berkeman

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    What kind of improvements? I always wondered why they didn't just trail a long wire behind them with an antenna at the far end to get it out of the main ionization envelope, but it sounds like they've done something else to maintain comms. Maybe relaying through a satellite overhead?
     
  8. Jun 19, 2015 #7

    davenn

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    got some links etc for that Russ ?

    I am also curious

    Dave
     
  9. Jun 22, 2015 #8

    Dotini

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  10. Jun 22, 2015 #9

    D H

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    That only applies to the Shuttle, which no longer flies. Russia's Soyuz, SpaceX's Dragon, Boeing's CST-100, and NASA's Orion are (or will be) capsules, and they all suffer (or will suffer) communications blackout during reentry.


    Thanks to the Shuttle's shape and reentry profile, parts of the Shuttle's tail could "see" the sky in high frequency communications bands. The TDRSS satellites provided the ability to communicate during what would otherwise be a very long (~25 minutes) communications blackout. Capsules can't do that. All they see during reentry is a hot sheath of plasma that completely surrounds the vehicle.

    Wire has a nasty tendency to become non-wire when heated to 5000 to 20000 degrees.
     
  11. Jun 24, 2015 #10

    Dotini

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