Re: Yet more FengYun debris

From: Richard Clark (rclark@lpl.arizona.edu)
Date: Thu Feb 15 2007 - 05:20:24 EST

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    On Wed, 14 Feb 2007, Christian Kj[ISO-8859-1] śrnet wrote:
    
    > Marco,
    >
    > I still have not found any debris pieces from the Chinese test 11 January
    > that are traveling in the opposite direction of the target satellite (i. e.
    > with an inclination of ca. 81.4 degrees). This leads to the conclusion that
    > the target was indeed struck from behind and the impact between the two
    > bodies created debris pieces in orbits with similar inclination around 98.6
    > degrees, as I explained in the previous message to the list.
    >
    > This also means that the ASAT-weapon must have had an orbital speed larger
    > than the target at impact, leading to a majority of debris particles
    > traveling in orbits with apogee larger than the target, Feng Yun 1C,
    > original orbit.
    
    It is unlikely that the ASAT vehicle was traveling at orbital velocity.
    It was put up in the path of the satellite. FY1C, traveling at leo
    orbital velocity hitting the 'slowly moving' ASAT in a collision that
    was fairly close to head-on.
    
    Within the limits of ascii drawing, the velocities, relative to a
    ground based observer below the impact point, would look
    something like (you're using a fixed width font I hope):
    
               *           <--------------------x
               ^                               FY1C
               |
             ASAT
    
    A naive application of conservation of momentum (scattering of pool
    balls at the break) leads to the conclusion nearly all of the debris
    should be expected in a lower orbit and essentially none in a higher
    orbit.
    
    However, in a hypervelocity impact like this, a shockwave is generated in
    the target (or combined projectile and target mass). This means that a
    significant fraction of the fragmentation debris was scattered by
    spallation, not the sort of elastic scattering we are familiar with from
    the pool table. Hence, in even a head on collision, a considerable amount
    of debris can be accelerated in the forward direction-- into higher
    orbits. A considerable amount would also have been accelerated rearward,
    but that will have decayed fairly quickly and not been cataloged. The 3D
    velocity and mass distribution of ejecta is also a function of the
    geometry of the target.
    
    Despite its role in the orbital dynamics of the resulting debris cloud--
    which has yet to be detected visually, I suspect that this discussion of
    fragmentation mechanics may be getting a little off topic. Ted?
    
    Richard Clark
    rclark@lpl.arizona.edu
    
    
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