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

From: David Tiller (dtiller@captechconsulting.com)
Date: Mon Apr 02 2012 - 11:51:26 UTC

  • Next message: Bob Christy: "Re: North Korea satellite: NOTAMs inconsistent with claimed sun-synchronous orbit"

    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 | dtiller@captechconsulting.com
    
    ________________________________________
    From: seesat-l-bounces+dtiller=captechconsulting.com@satobs.org [seesat-l-bounces+dtiller=captechconsulting.com@satobs.org] on behalf of Ted Molczan [ssl3molcz@rogers.com]
    Sent: Sunday, April 01, 2012 10:46 PM
    To: seesat-l@satobs.org
    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:
    
    http://www.kcna.co.jp/item/2012/201203/news28/20120328-40ee.html
    
    "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
    
     YELLOW SEA AND NORTH PACIFIC, LUZON.
     ACCORDING TO INFORMATION FROM NORTH
     KOREA VIA IMO, ROCKET LAUNCHING.
     IMPACT HOUR 2200Z TO 0300Z COMMENCING
     DAILY 11 TO 15 APR.
     IMPACT AREAS BOUNDED BY
     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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