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

From: Brian Weeden (
Date: Sun Apr 08 2012 - 14:47:09 UTC

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

     I think there is another possibility - that they are trying to do
    everything they can to limit the ability of Japan, South Korea, US, and
    other countries to criticize this launch as non-peaceful.  I believe they
    watched what Iran did in 2009 with great interest, especially the lack of
    any outcry or criticism from the US, and are trying to model their program
    after what Iran did.  That means doing everything on the surface that one
    would do if it were indeed a launch of a satellite for peaceful purposes -
    pre-launch notifications, warnings to sailors and airmen, putting up a
    remote sensing satellite into a sun-sync orbit, etc - even if they don't
    have the capability to actually do all those things.   A "pseudo" space
    launch, as it were.
    Another good analogy is the 2010 Chinese ASAT test. It was reportedly the
    same system as used in 2007, but the target was another ballistic object
    and it was labeled a "missile defense test".  This was what China learned
    from USA 193 - it's ok to test and develop your missile defense technology,
    just as long as you do it in a "responsible" manner and don't create
    long-lived space debris.
    I think it's a pretty wild claim for a country that has never successfully
    put an object into orbit before to claim they're going to put their first
    satellite up at a fairly high altitude (500 km) and in a very precise set
    of orbital parameters (sun-synchronous) and have that satellite return data
    (even though they don't have the tracking network or C2 network to do so).
     But, that's what you do if you are a spacefaring country with a serious
    space program, so that's the way the North Koreans are going to pitch this.
    So I wouldn't call it lying, more like marketing.  Which may be lying from
    a certain viewpoint :)
    On Sun, Apr 8, 2012 at 9:44 AM, Jonathan McDowell
    > 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
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