My analysis of the Chinese ASAT test can be found at http://mit.edu/stgs/spaceprograms.html (there is a link to a pdf of a presentation I gave about two weeks after the test on that page.) I get very different numbers for some of the orbital velocities than have been discussed in this thread. I also found that the ASAT hit almost head on (30 degrees off the "port bow," if you will, and from slightly below.) Best regards, Geoff -----Original Message----- From: Richard Clark [mailto:rclark@lpl.arizona.edu] Sent: Thursday, February 15, 2007 5:20 AM To: satellite list (SeeSat) Subject: Re: Yet more FengYun debris On Wed, 14 Feb 2007, Christian Kj[ISO-8859-1] ærnet 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 ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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