Re: North Korea satellite: NOTAMs inconsistent with claimed sun-synchronous orbit

From: Brian Weeden (
Date: Mon Apr 02 2012 - 12:26:24 UTC

  • Next message: Ted Molczan: "RE: North Korea satellite: NOTAMs inconsistent with claimed sun-synchronous orbit"

    Figure 2 in this paper shows a plot of inclinations necessary for a
    Sun-sync orbit at various altitudes (assuming zero eccentricity):
    Ted, I agree with your overall point about the projected launch Az not
    right for a SSO orbit at 500 km, but my math is coming out differently.
     For a latitude of 39.66 and an Az of 192.3 I get an inclination of 99.44
    degrees.  My excel formula for the inclination is
    where B5 = latitude and B6 = Az
    I think one of us may have a math error (likely me), so if someone could
    check my formula I would appreciate it.
    On Mon, Apr 2, 2012 at 7:51 AM, David Tiller
    > Ted,
    > Thank you for your (as always) excellent analysis.
    > It seems that there are two parameters that are used to compute the
    > particulars of a sun-synchronous orbit - orbital altitude is used to derive
    > the correct orbital inclination which then drives the launch azimuth based
    > on latitude. Your analysis assumes that the stated launch altitude is
    > correct and the launch azimuth is incorrect.
    > What orbital altitude would be correct for a sun-synchronous orbit
    > assuming that the launch azimuth will be as the DPRK stated?
    > --
    > David Tiller
    > Lead Consultant/Architect | CapTech
    > (804) 304-0638 |
    > ________________________________________
    > From:[seesat-l-bounces+dtiller=
    >] on behalf of Ted Molczan [
    > Sent: Sunday, April 01, 2012 10:46 PM
    > To:
    > Subject: North Korea satellite: NOTAMs inconsistent with claimed
    >  sun-synchronous orbit
    > North Korea claims that its upcoming rocket launch will place a satellite
    > in a 500 km, sun-synchronous orbit:
    > "It weighs 100kg and will circle along the solar synchronous orbit at
    > 500km high altitude."
    > The sun-synchronous claim is inconsistent with the NOTAM coordinates North
    > Korea has issued for the impact zone of the
    > rocket's two stages:
    > NAVAREA  NO.12-0174       Date:2012/03/19 12 UTC
    >  DAILY 11 TO 15 APR.
    >  A. 35-12-25N 124-52-23E
    >    35-12-13N 124-30-34E
    >    35-55-20N 124-32-10E
    >    35-55-10N 124-50-25E.
    >  B. 15-08-19N 124-46-15E
    >    15-09-35N 123-45-27E
    >    19-24-32N 123-54-26E
    >    19-23-08N 124-45-13E.
    >  CANCEL THIS MSG 150400Z APR.
    > Stage 1 would impact in zone A; stage 2 in zone B.
    > The launch site is located at 39.660107 N, 124.705203 E.
    > To be sun-synchronous, a 500 km orbit requires an inclination of 97.42
    > deg. At the latitude of the launch site, a
    > trajectory that directly ascends to that inclination requires a launch
    > azimuth of approximately 192.3 deg (12.3 deg west
    > of due south). The azimuth from the launch site through the various impact
    > zones downrange should agree closely with
    > this value, typically within a degree or so, absent any significant
    > yaw-steering (aka dogleg) early in the ascent.
    > The azimuth from the launch site to the midpoint of the southern boundary
    > of the 2nd stage's impact zone (approx. 15.15
    > N, 124.26 E) is 181.0 deg, which is far from the required 192.3 deg.
    > I considered the possibility of an eastward dogleg early in the ascent,
    > but the trajectory would have to turn toward
    > approximately 192 deg azimuth well before the 2nd stage ceased firing, in
    > which case the 2nd stage's impact zone should
    > be oriented with its east and west sides pointing roughly toward azimuth
    > 191 deg, but they do not. The west side points
    > toward azimuth 181.8 deg, and the east side 179.8 deg - again far from the
    > required value, and essentially identical to
    > the azimuth calculated from the launch site. Therefore, there is no
    > dogleg, which is not surprising, since it would
    > involve overflying the Korean peninsula, probably including South Korea.
    > I do not see how North Korea could reach a sun-synchronous orbit from the
    > new launch site without risk to populated
    > areas. Launching directly toward the required 192.3 deg azimuth would
    > result in a trajectory that skirts China's east
    > coast near Shanghai. The rocket's second stage would overfly Taiwan,
    > before impacting in a zone bordering within perhaps
    > 50 km of the west coast of the northern Philippines.
    > To give a *very rough* idea of the effect of launching directly toward
    > azimuth 192.3 deg, I have adjusted the longitudes
    > of North Korea's NOTAMs:
    >  A. 35-12-25N 123-42E
    >    35-12-13N 123-20E
    >    35-55-20N 123-33E
    >    35-55-10N 123-51E
    >  B. 15-08-19N 119-38E
    >    15-09-35N 118-56E
    >    19-24-32N 119-43E
    >    19-23-08N 120-34E
    > I very much doubt that North Korea plans for its rocket stages to fall in
    > the zones I have estimated, but it is for
    > North Korea to explain the inconsistency between the orbit it claims to be
    > targeting and the NOTAMs it provided.
    > Ted Molczan
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