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

From: satrack@libero.it
Date: Wed Apr 11 2012 - 19:54:20 UTC

  • Next message: Bob Christy: "Re: R: Re: North Korea satellite: retrograde ground track displayed in launch control centre"

    I used Ted's TLEs to reproduce the same 3D perspective, for both 97.5 and 94.5 
    deg. The first one seems to
    match well. 
    By the way, in the original picture, the orbit is plotted ECI, so the Earth 
    rotates with respect
    to the orbit. This means that the same perspective is obtained only at the 
    correct time, which is
    around 02.45 UTC, if using Ted's TLEs. 
    At the previous link I uploaded also the workspace, in case someone wants to 
    work with these
    >----Messaggio originale----
    >Da: bob@zarya.info
    >Data: 11-apr-2012 18.49
    >A: "Seesat-L"<SeeSat-L@satobs.org>
    >Ogg: Re: North Korea satellite: retrograde ground track displayed in launch	
    control centre
    >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: 
    >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.
    >> The relevant scene appears for several seconds beginning at 01:56 elapsed 
    >> 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-
    >> 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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