Daft Question:

Discussion in 'Satellite TV, Sky TV & FreeSat' started by GasDad, Feb 5, 2009.

  1. GasDad

    GasDad
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    My middle son asked me this the other day - I didn't have a answer.

    "What happens if the sky satellite gets hit by a some space junk?"

    Spent 10 minutes explaining orbital mechanics with an orange and how things fall around the earth. Then how the Clarke (or geostationary orbit) works, and why there wasn't much junk up in that high an orbit. :lesson:

    He got all that - and said ok what about a meteorite ?

    Didn't have an answer :lease:
     
  2. Miss Chief

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    Very unlikely given the sheer amount of, well, space up there. The satelite is probably about the size of a Chest freezer or washing machine and even with the solar panels (which i assume it has to give it some source of power) it's still very small given the size of the atmosphere around earth. I'm sure someone could do a calculation to 26,000 miles from the earth's core then the volume taken up by the earth, subtract the earth's volume from the total volume and then you have the amount of space that the satelite is hiding in. Not so much a needle in a haystack as a needle in all the hay made in all the world every decade kind of thing.

    Small meteorites that stand a chance of hitting it stand, at a guess, somewhere close to odds of 1,000,000,000,000 to one of hitting a satelite. possibly even higher.
     
  3. Martin J.

    Martin J.
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    There are four satellites at 28.2°E, Astra 2A, 2B, 2C and 2D. They're all in slightly different positions ("slightly" in space terms, being miles apart), so if one were destroyed, only the channels on that satellite would be effected.

    Larger meteors can be seen coming, so conceivably the satellites could be moved out of the way, then back again, but in reality if there were a meteor large enough to destroy them all, we'd have bigger worries than a loss of our television signals.
     
  4. GasDad

    GasDad
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    Thanks for that - Ok I'll do the calculation - yes I know I'm answering my own question - but I've had a coffee since asking it.;)

    The volume isn't strictly relevant - given meteors travel through that whole volume. If you say the satellite is a metre cubed (reasonable) - it's sitting on a sphere that covers 42,000,000^2 x pi x 4 m2. (radius of geostationary orbit squared x pi x 4)

    Apparently around 100,000 meteorites larger than 10g hit earth each year (so they were a lot larger whilst in space) - all will have travelled through that area above.

    That gives about 1 in 221,000,000,000. chance of a hit in a year. So I guess it is fairly safe. (though this ignores meteors that miss earth but still pass through the sphere). Can't find any figures for smaller meteorites though - so the odds a probably a few orders of magnitude smaller than that.

    I'll get my son to do the calcs for himself, and work out why sky etc don't have a policy for this.
     
  5. BrianMc

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    Sky will have a policy for this! Or rather SES (the Luxembourg firm which operates the satellites) will have - but they don't talk about it. The satellite "fleet" which transmits to the UK are in an (I read once) 80km (or was it mile?) "cube" - so the chances are tiny of all failing (which can be a component failure or a meteor strike). The channels are distributed around the different satellites as well.

    The Sky satellites are also in geostationary orbit at 25000km. Most space junk inhabits "low earth orbit" at about 200-300km.

    If a satellite fails any popular channels on it will be moved. Some minor channels may be taken off-air until a new one can be either launched or repositioned.
     
    Last edited: Feb 5, 2009
  6. nikonuser11

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    Sky I'm sure will have Greenflag or RAC cover in case of any 'offsite' repairs.........:rotfl: sorry couldnt resist.


    However, if one was hit or failed the others can transmit PLUS SKY will have (or as Brianmc rightly pointed out SES) a reciprocal arrangement to 'piggyback' someone elses satellite in case of downtime............makes sense really. Good question by your middle son:lesson:
     
  7. Downinja

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    Think this happened to the sat that was carrying ITV last night :D
     
  8. GasDad

    GasDad
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    I've been reading up this - and that all seems correct. Love to know what they put the odds at. (Presumably they expect erosion of the solar panels over a period of time etc).

    Question remains as to whether there are more meteors in the plane of the epileptic, which is also roughly where most satellites are.

    Just in case it comes up in a pub quiz its 22000miles / 36000km above sea level. Hence I used 42000km as the radius of earth is 6000km.

    I presumed that would happen, rather than the special heights team getting called out.:)

    Cheers

    James
     
  9. davemurgatroyd2

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  10. Stackers

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  11. Naaktgeboren

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    It is entirely possible that a collision could take place between DSP-F23 and a satellite.

    If a collision does take place that could effectively mean the Arc would be filled with millions of lethal fragments circulating which in turn would destroy or damage many satellites as a result.

    In such a scenario it would be hundreds of years before the Arc is usable once again.
     

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