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The Celestial Junkyard

Discussion in 'Fred's House of Pancakes' started by airportkid, Jul 24, 2007.

  1. airportkid

    airportkid Will Fly For Food

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    The crew at the space station today jettisoned a 200 pound camera mount and a heavier ammonia tank by literally throwing them into space. NASA doesn't like to add to the clutter up there (see subtitle of this topic) but they hadn't any choice in this case. The mount and tank are expected to fall back to earth within a year or so and burn up in the atmosphere, so as clutter they aren't expected to present much additional hazard.

    But here's my question. The junk was hurled (according to the article) opposite the space station's direction of travel (to maximize separation distance right away, I guess).

    But why not have flung it straight at the earth? They're only 200 miles up; wouldn't shoving it at the earth get it burnt up within 48 hours instead of hanging around in orbital space for a year? Assuming the astronaut could give the junk an initial velocity vector of 5MPH earthward, that's 40 hours to the surface without any gravitational assistance - gravity would of course accelerate the junk to much higher velocity so the whole trip might take 30 hours (without ever reaching earth since atmospheric friction would incinerate the junk before it got all the way down).

    Anybody have any ideas on this?

    Mark Baird
    Alameda CA
     
    #1 airportkid, Jul 24, 2007
  2. vtie

    vtie New Member

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    It's not that simple. You have to combine the speed of the spacecraft and the throwing speed in a vectorial way. Because of the huge speed of the spacecraft, all you can achieve is a tiny change in the overall magnitude and direction of that speed (the so-called delta V). The consequence is that you will manage to modify the orbit a little bit, but it will still be an orbit around the Earth nevertheless.
    The point is that you need to combine the throw velocity with the speed of the spacecraft, and calculate the new orbit that results from this
    To really "throw" something directly to the Earth in the way you think about it, you would need a huge initial delta V. You would need another rocket to achieve that!

    Then the question comes: what is the optimum way to use that delta V? What you want to have is a new orbit that brings the debris as close to the Earth as possible. Technically spoken, this is going to be an elliptical orbit with it's pericenter as low as possible. Starting from a more or less circular orbit, the optimum way to achieve this is to minimize the velocity. This can be done by launching it opposite to the travel direction, so that both vectors subtract from each other.
     
    #2 vtie, Jul 24, 2007
  3. Jim1eye

    Jim1eye Shaklee Ind Distributor

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    STS-117 just delivered Solar Panels and Trusses to the ISS last month. With that stuff out of the cargo bay, I think this junk would have fit. I guess there is no one left at NASA without any vision or foresight.

    Replace...Reuse...Recycle
     
    #3 Jim1eye, Jul 24, 2007
  4. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    <div class='quotetop'>QUOTE(vtie @ Jul 24 2007, 02:35 AM) [snapback]484034[/snapback]</div>
    What's truly sad is that I actually understaood every word of that. :blink:
     
    #4 TonyPSchaefer, Jul 24, 2007
  5. qbee42

    qbee42 My other car is a boat

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    <div class='quotetop'>QUOTE(TonyPSchaefer @ Jul 24 2007, 09:05 AM) [snapback]484074[/snapback]</div>
    Yes, and it was well written. For real fun look at the orbit of a pair of small shepherding moons, or a librating geosynchronous satellite. Or how about trying to catch up with another orbiting body, so you slow down for a faster angular velocity.

    Tom
     
    #5 qbee42, Jul 24, 2007
  6. ohershey

    ohershey New Member

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    <div class='quotetop'>QUOTE(qbee42 @ Jul 24 2007, 06:17 AM) [snapback]484078[/snapback]</div>
    Short of frame dragging, that one's my favorite.
     
    #6 ohershey, Jul 24, 2007
  7. Cheap!

    Cheap! New Member

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    <div class='quotetop'>QUOTE(Mad Hatter @ Jul 24 2007, 01:30 PM) [snapback]484228[/snapback]</div>
    What ever happened to de-orbiting tethers?
     
    #7 Cheap!, Jul 24, 2007
  8. qbee42

    qbee42 My other car is a boat

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    <div class='quotetop'>QUOTE(Cheap! @ Jul 24 2007, 03:39 PM) [snapback]484271[/snapback]</div>
    I think a real long one with an anchor on the end! :blink:

    Tom
     
    #8 qbee42, Jul 24, 2007
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