RE: shoot down questions

From: Richard Clark (
Date: Sun Feb 17 2008 - 11:52:11 UTC

  • Next message: Russell Eberst: "2008FEB16.OBS"

    For the fractional orbit after intercept it is sufficient to view to
    within a few minutes of the time of the unperturbed satellite pass for
    your location.
    To investigate dispersion of debris use software that produces cartesian
    vectors at a specified time (e.g. the instant you think the intercept
    will occur). Kelso's Trakstar will do this. Lots of others will too.
    Use the EFG (rotating framework) option for the vectors.
    Take that vector and generate other vectors for sample debris fragments
    with dv of +/- 150 m/s (I think this is roughly the STS deorbit burn) in
    the velocity direction. (the '-' will be your reentry candidate) Also try
    similar dv in crossrange and radial directions. And try smaller velocity
    impulses too to investigate the dispersion of debris that will be left in
    Then use vec2tle to generate TLEs from these vectors.
    This is a little tedeous, but can all be done with readily available
    software for dos/windows. I don't know if the functionality of vec2tle
    has ever been made available on other platforms.
    Looking forward to others suggesting more streamlined ways to do this:-)
    Richard Clark
    On Sat, 16 Feb 2008, Floyd Weaver wrote:
    > I tried to send this last night but it appears to not have went through so I
    > will try it again. I did get to see ISS/STS on sat eve but not USA 193.
    > Here is what I tried to send...
    > I have been thinking about this shoot down and trying to figure some things
    > out as to my chances of seeing something reenter over Lebanon PA USA. I have
    > not seen the sat yet but hope to see it in a day or two as the evening
    > visibility windows is just opening for us. I have been putting my somewhat
    > limited knowledge of orbital mechanics and kinetic energy to use. I still
    > have questions and maybe need my thinking straightened out.
    > After an interceptor hit any pieces that were not vaporized, will reenter
    > within a half orbit or so if there speed was reduced enough to drop the
    > orbit perigee into the atmosphere. I guess the amount that reenters within a
    > half an orbit depends on how the intercept goes. Hit a solar panel or radio
    > antenna, and I suspect most of the sat will NOT reenter within half an
    > orbit. But even a perfect hit would be virtually impossible to cause
    > everything to reenter within half an orbit. Seems to me the best place to be
    > would be about half an orbit ahead of the sat when intercept occurs. But
    > there will be a lot more reentries at other locations.
    > To see these piece reenter is it a good idea to be out all the time the
    > orbital plain is above the horizon or maybe above 10 or 20 degrees? I am
    > sure most of the pieces will not be catalogued so there will not be
    > predictions, you just have to be out looking when they reenter. And things
    > will rapidly get spread out in the orbital plain so much so that you could
    > not just look within a few minutes of when the sat would have been there.
    > How quickly will the debris spread out to the side of the orbital plain thus
    > widening the plain? This would increase the time someone would have to be
    > out. And would it be worth looking during the daytime? I suppose for the
    > bigger piece, they should be visible. The last pieces to reenter should be
    > the larger pieces and maybe they will be catalogued.
    > If anyone can give more tips on when to look for debris reentry I would
    > appreciate it or straighten me out if I am incorrect in my thinking.
    > I love to see reentries (course lots of these will be little pieces and not
    > put on a show like a complete sat or rocket body) and am ready to spend some
    > time out watching.
    > Thanks
    > Floyd Weaver
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