RE: USA-193 Interception

From: Geoffrey E. Forden (forden@MIT.EDU)
Date: Tue Feb 19 2008 - 16:09:48 UTC

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    As promised, here is the link to my analysis of the USA193/LEAP
    other related analyses can be found at
    This is based on an analysis of the debris pattern from the FY-1C collision
    which show that the ANGLE the debris comes off at is correlated with the
    direction of the interceptor (sorry, that diagram isn't shown in the paper
    posted but Id be glad to send it to anyone interested. seesat quite rightly
    doesn't allow attachments.)
    I believe that the LEAP interceptor will not use its third stage because
    that would drive the closing speed well above the announced closing speed of
    9.8 km/s  (my simulation gives 9.4 km/s if it does not use its third stage
    but I attribute that to press conference rounding error.)  The second stage
    will splash down about 500 km way from the interception point--about 1000 km
    away from the ship--and the first stage much closer to the ship than that.
    Since the NOTAM extends about 1,500 km from the interception point I
    predict, which is much greater than any of the stages.
    If the interception point happens at the place I predict or earlier on the
    satellite's trajectory, observers on Oahu should be able to see it by the
    flash mentioned in a previous post.  By the way, seeing it or not seeing it
    would be a great way of settling this issue!  Again, my predictions for Oahu
    Az: 243.7
    El: 10.5
    RA: 44.5
    Dec: 21.2
    Unfortunately, the satellite track as it passes over the NOTAM takes well
    outside the angular range of any fixed optical instrument.  But if is
    possible to control the pointing of your scope as the satellite moves, I
    could give you a set of RA/Dec or AZ/EL as a function of time.
    -----Original Message-----
    From: Bob Christy [] 
    Sent: Tuesday, February 19, 2008 9:00 AM
    Subject: USA-193 Interception
    Using the Fengyun interception as a reference, the evidence is that the
    interception cannot be treated as the sort of ballistic collision that we
    saw in school science experiments.
    At the point of collision, two objects will come together with a closing
    speed near that of orbital velocity. The catastrophic disruption of USA-193
    and its interceptor will produce a debris cloud spreading evenly in all
    directions but, overall, still having USA-193's original orbital
    Witin the cloud will be a collection of trajectories near to the original
    inclination but spreading either side, and there will be a range of apogees
    and perigees due to the vertical component of the spreading.
    Fragments leaving the cloud with the lowest orbital velocity will hit the
    upper atmosphere fairly quickly - it's a little like Soyuz or Shuttle having
    fired a retro-rocket. My guess (intentional word) is that the first
    re-entries will occur about one quarter to one half orbit after the
    fragmentation. The remainder will be spread over a number of days.
    The choice of the interception orbit ground track is a very good one.
    Optical observation is possible immediately after the collision, and the
    next three circuits of the Earth pass over very little land. 
    The area laid out in the NOTAM is not to defined catch post-collision
    fragments because there will not be any heading in that direction. The SM-3
    missile is three-stage so the area covers the splashdown of stages 1 and 2,
    and, in the event of a miss, stage 3 and it's warhead also.
    I have posted some expanded notes and some maps here:
    Bob Christy
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