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

From: Bob Christy (
Date: Sun Apr 08 2012 - 14:30:13 UTC

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

    A dog leg is a quite ambitious in the face of having no experience of 
    controlling something in orbit. If we take Iran's efforts as an example, 
    don't be surprised if "500 km, sun-synchronous" turns out to be 200 x 
    500 km, 90.
    I vote with Jonathan's hypothesis 3.
    Bob Christy
    On 08/04/2012 14:44, Jonathan McDowell wrote:
    > 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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