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

From: Jonathan McDowell (
Date: Sun Apr 08 2012 - 13:44:50 UTC

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

    I am wondering if "Unha-3" means "3-stage Unha", not "3rd Unha".
    Consider a scenario in which stage 2 is injected over North Korea at 150
    km with an inertial velocity of 7.0 km/s and an inertial azimuth of 178
    deg (rotating frame azimuth of 181 deg as required by the NOTAMs). It
    then  reaches a -2350 x 500 km x 88 deg orbit, with apogee over the
    equator at 123E
    Then suppose the payload and a third stage are yawed by 50 degrees and
    make a 1.6 km/s burn. For a third stage empty mass of 50 kg (say)
    and a satellite of 100 kg, and a solid motor of Isp = 250 s,
    this would require 150 kg of prop for a total upper composite mass
    of 300 kg. Is that outside the 2-stage Unha's performance?
    If I were NK, this is absolutely how I would attempt to launch
    a sun-sync satellite - it's very similar to the strategy used
    by some early US Delta launches. A lower stage dogleg is not required.
    So Ted, I think you are premature in your conclusions. I see four scenarios:
    1. - Ted's scenario in which the NK are flat out lying. Certainly possible
         but I don't think this is the most likely explanation.
    2. - My scenario in which a third stage equatorial dogleg achieves sun-sync.
    3. - Translation confusion somewhere along the chain where "polar orbit"
       and "sun-sync" orbit have been conflated because some poor translator thought
       that "sun-sync" sounded more technical and impressive - the two concepts
       almost always go together these days since ninety-something percent of
       modern polar orbit satellites are sun-synch.
    4. - Lying somewhere else along the chain. For example,
       the vice director of the Space Development Department is a non-technical
       party appointee who has ordered his engineers to launch a sun sync satellite,
       and his scared engineers are lying to him and hoping that he won't notice
       the difference, or will forgive them if they at least get a satellite up....
     - Jonathan
    Seesat-l mailing list

    This archive was generated by hypermail 2b29 : Sun Apr 08 2012 - 13:46:14 UTC