Re: North Korea satellite: retrograde ground track displayed in launch control centre

From: Bob Christy (bob@zarya.info)
Date: Wed Apr 11 2012 - 16:49:39 UTC

  • Next message: Peter Wakelin: "SATOBS 2012 April 10 (cont)"

    I have used a piece of iPad software to reproduce the screen image 
    showing the orbit. It tells me the inclination is 97.4.
    
    There are copies of the two images here: 
    http://www.zarya.info/Gallimaufry/Unha3SS.php#3D
    
    Bob Christy
    
    On 11/04/2012 02:36, Ted Molczan 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 ground
    > 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
    >
    >
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