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

From: Bob Christy (bob@zarya.info)
Date: Wed Apr 11 2012 - 20:10:06 UTC

  • Next message: Ted Molczan: "RE: North Korea satellite: retrograde ground track displayed in launch control centre"

    Agreed about the view it represents. It's also how Orbit Architect 
    depicts it so I am confident of the inclination it represents - 97°.5. 
    Ted and I have just been discussing it offline.
    
    If you look at the video screen grab at 
    http://www.zarya.info/Gallimaufry/Unha3SS.php#3D there is an 'extra 
    island' in the Pacific about 150° azimuth from Taiwan. It is the 
    satellite depicted on the orbit at about the time of separation from 
    Unha 3. The location is close to the one I estimated on the original map 
    near the top of my web page.
    
    It represents the situation about 10 minutes after launch and is 
    consistent with the NOTAM areas and a dogleg by stage 3. The only 
    question is whether it is genuine, and there doesn't seem to be anything 
    to say it isn't
    
    Bob Christy
    
    On 11/04/2012 20:54, satrack@libero.it wrote:
    > 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.
    >
    > http://www.satflare.com/CmpInc97.html
    >
    > 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
    > views.
    >
    > Regards,
    > Simone
    >
    >
    >> ----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:
    >> 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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    >>>
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