Re: KMS-4 orbit: JSpOC versus DPRK claims

From: Jonathan McDowell via Seesat-l <seesat-l_at_satobs.org>
Date: Sun, 7 Feb 2016 13:52:33 -0500
.. or they are referring heights to a different ellipsoid

On 7 February 2016 at 13:25, Brian Weeden via Seesat-l <seesat-l_at_satobs.org>
wrote:

> Yes, that would be my guess - JSpOC has it right, and the DPRK either
> published the "desired" orbit, or messed up the maths.
>
>
>
> ---------
> Brian
>
>
> On Sun, Feb 7, 2016 at 1:11 PM, Marco Langbroek via Seesat-l <
> seesat-l_at_satobs.org> wrote:
>
> >
> >
> > Hi all,
> >
> > I noted that the orbital parameters given in this DPRK announcement here:
> >
> >
> >
> https://soundcloud.com/martyn-williams-6/voice-of-korea-on-kwangmyongsong-4-launch
> >
> > ...namely perigee 494.6 km, apogee 500 km, inclination 97.4 deg
> >
> > is inconsistent with what we so far have from US tracking of the object.
> > The
> > first few sets of orbital elements published by JSpOC on Space-Track give
> > (calculated from eccentricity and Mean Motion values) these values:
> >
> > - perigee 465 km, apogee 502 km, inclination 97.5 deg
> >
> > There is a clear difference in the apogee altitude here: 465 km according
> > to
> > JSpOC, 494.6 km according to the DPRK.
> >
> > Now, this could be due to initial inaccuracies in the JSpOC tracking
> data.
> > The
> > first few elsets always have some variation and are less accurate
> usually.
> >
> > Yet given the magnitude of the difference, I doubt this a bit.
> >
> > Instead, and assuming that the values in the DPRK announcement are not
> > based on
> > actual North Korean tracking but represent a pre-launch desired orbit, I
> > wonder
> > if this is perhaps an indication that the satellite ended up in an orbit
> > with
> > lower perigee than intended?
> >
> > - Marco
> >
> >
> > -----
> > Dr Marco Langbroek  -  SatTrackCam Leiden, the Netherlands.
> > e-mail: sattrackcam_at_langbroek.org
> >
> > Station (b)log: http://sattrackcam.blogspot.com
> > Twitter: _at_Marco_Langbroek
> > PGP key: http://tinyurl.com/kur7xm8
> > -----
> >
> >
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> >
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Received on Sun Feb 07 2016 - 12:53:00 UTC

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