It's good to see the similarity between this and my own plot drawn from a starting point at the other end of the track: http://www.zarya.info/Gallimaufry/Unha3SS.php . The two support each other nicely. I looked at a number of published ascent trajectory diagrams from real launches to work out where second/third stage separation and ignition might occur, and came to the conclusion it would be about 600 km down range from the launch site. The transition to sun-synchronous orbit is not instantaneous. The ground track follows an arc as the 'sideways' component of the velocity increases through the duration of the third stage motor firing. Unha and the payload then settle onto the final track when the motor burns out. 'Walking back' the final track on my plot produces an intersection between the two paths in a similar location to the one on Ted's diagram, which is good news! All we need now is to see the reality. Bob Christy On 11 Apr 2012, at 02:36, "Ted Molczan" <ssl3molcz@rogers.com> wrote: > Included in some of the video shot by journalists covering North Korea's upcoming rocket launch, are launch control > display screens depicting a southbound ground track that to the eye looks close to that of a sun-synchronous satellite > orbit. It has been discussed on the NSF and NK forums. I have been working to estimate the orbit implied by the grou > track and to evaluate its consistency with the location of the launch site, NOTAMs, and other information issued by > North Korea. > > The first images I saw had insufficient resolution or coverage to confidently estimate the orbit. Fortunately, late last > night Charles Vick informed me of the following video, which is the clearest I have seen yet: > > http://www.youtube.com/v/GpjGwG414rY&hl=en_US&feature=player_embedded&version=3 > > The relevant scene appears for several seconds beginning at 01:56 elapsed time. > > Notice that the track begins on the other side of the Earth, rises above the northern limb, then proceeds south over > China, the Korean peninsula and so on. The track appears to be a 3D representation of the initial orbit around the > Earth. > > Based on a notional launch on 2012 Apr 12 at 02:30 UTC, and assuming a 500 km circular orbit, I estimate that the orbit > is inclined approximately 94.5 deg: > > 1 79802U 12103.11415511 .00000000 00000-0 00000-0 0 05 > 2 79802 94.4500 182.0500 0002000 359.9726 179.8827 15.21000000 00 > > I estimated the inclination and RAAN by trial fit to a couple of reasonable clear land marks visible on the display. > Since the orbit has been plotted as a 3D representation, there is potential for parallax error in the ground track, but > it is mitigated by the more or less perpendicular vantage point. I estimate the RAAN and inclination are accurate to > within several tenths of a degree. > > The epoch is of no special significance; it and the mean anomaly have been chosen to place the orbit near the launch > site about 4 min after lift-off, which is a useful rule of thumb to estimate the location of a newly satellite within > its orbit. > > I was especially interested to determine whether the 94.5 deg orbit intersects with the 88.7 deg inclined ascent > trajectory, and whether the location is plausible for the 3rd stage firing. Here is a plot of both trajectories: > > http://satobs.org/seesat_ref/misc/NK-2012-retrograde-1a.jpg > > Here is a view near the ascent trajectory: > > http://satobs.org/seesat_ref/misc/NK-2012-retrograde-2a.jpg > > The point of intersection is near 28.25 N, 124.5 E, about 1270 km downrange of the launch site, which seems to be in > rough agreement with the plot of altitude vs. range in this recent analysis by David Wright (see Fig.2): > > http://allthingsnuclear.org/post/20730991602/a-comparison-of-north-koreas-unha-2-and-unha-3 > > The orbit is not sun-synchronous, but better than the 88.7 deg orbit implied by the NOTAMs, for the stated purpose of > the satellite. Sun-synch orbits precess +0.9856 deg/d. The 88.7 deg orbit would precess at -0.1730 deg/d; the 94.5 deg > orbit would precess 0.5917 deg/d. > > To be precisely sun-synch, a 500 km orbit must be inclined 97.4 deg. The apparent nearly 3 deg deficit may be an > indication of the performance limitation of the launcher. I do not exclude the possibility that the displayed track was > faked to mislead the news media, but it should not have been more difficult to produce a high-fidelity fake, assuming > the work was done by the trajectory specialists. Considering the relative position of the numerals 4 and 7 on a keypad, > a simple, honest typo also cannot be excluded. > > Ted Molczan > > > _______________________________________________ > Seesat-l mailing list > http://mailman.satobs.org/mailman/listinfo/seesat-l _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-l
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