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

From: Bob Christy (
Date: Mon Apr 02 2012 - 09:25:35 UTC

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

    North Korean descriptions of this launch hint that it will produce:
    1 - a stabilised platform for a sophisticated high-resolution camera system
    2 - 500 km circular orbit, a launch profile that strongly implies a re-start by the upper stage, but a direct ascent is always possible
    3 - a sun-synchronous orbit, that Ted has shown would require a dog-leg.
    That's pretty ambitious for a country where there is no previous history of launching, operating or controlling satellites. I tend to look at it in comparison with Iran's efforts where, behind the hype, everything has been done in a simple manner with short-lived payloads.
    So, based on the evolution of Iran's satellites, and assuming that there actually is an orbital launch behind the propaganda and political sabre-rattling:
    1 - the operational lifetime is likely to be short,
    2 - if the payload is stabilised, it's likely to be a gravity-gradient boom and the satellite will have a wobble, not a particularly steady platform for what is likely to be a relatively simple imaging device,
    3 - given that the objective is to get something into space, and looking at other nations' first successes, don't be surprised to see something more like 200 x 500 km. Iran often refers to orbits by only their apogees, it looks better than it really is,
    4 - with tongue firmly in cheek, anything above 90° inclination with a short lifetime might loosely be described as sun-synchronous, the local time below is not going to change much over a few days,
    5 - aside from the fact, as Ted has pointed out, that it isn't going to happen, a dog-leg is unlikely because it's another complication that can lead to failure even if the LV has the brains and control system to do it. N Korea has a similar problem to Iran, there is a narrow corridor out of the country that can be followed by a satellite or missile launch without overflying another's territory, and that dictates the inclination. There are some maps showing the Iranian corridor here:
    Propaganda is not the easiest of languages to interpret, especially when it first has to be translated into English.
    Another couple of weeks, we'll know the answer...... Maybe.
    Bob Christy
    On 2 Apr 2012, at 03:46, "Ted Molczan" <> wrote:
    > 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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